50 faits sur l'espace qui vont vous étonner et vous stupéfier

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Transcript

00:00:00 Colonizing other planets is a bit like the ultimate cosmic adventure.

00:00:04 This challenge has fed the imagination of humans for centuries,

00:00:08 and we still dream about it today.

00:00:10 One of the best candidates is the planet Mars.

00:00:15 It's not surprising.

00:00:16 Mars is a rocky planet that looks like Earth in many ways,

00:00:20 and its surface even has old traces of water.

00:00:24 This makes it a destination of choice for colonization.

00:00:28 Many scientists are working on projects to send humans there

00:00:32 to establish a permanent community.

00:00:35 But are there other candidates?

00:00:39 There are many planets and moons in our solar system.

00:00:42 So why not go to other destinations?

00:00:46 For example...

00:00:47 Ceres.

00:00:49 Ceres is a real gem.

00:00:52 It's a dwarf planet, not a whole planet, like Pluto.

00:00:57 It's in the asteroid belt between Mars and Jupiter.

00:01:01 It's the closest planet to the Sun, and it's tiny.

00:01:05 It's about the size of Texas.

00:01:08 So why choose it?

00:01:11 Because Ceres could house precious resources.

00:01:15 Its surface is covered with craters and other geological features.

00:01:22 Scientists think there's a thick layer of ice underneath.

00:01:27 So deep down, there could be a liquid ocean.

00:01:32 If that's the case, Ceres could be a precious resource for our future missions.

00:01:37 It could provide the water necessary for our exploration of the solar system.

00:01:42 So can we colonize it?

00:01:46 And if so, how?

00:01:48 Many space enthusiasts have proposed this idea.

00:01:53 To colonize Ceres, we'd have to use the same methods as those used to build colonies on the Moon,

00:01:59 Mercury, and on Jupiter and Saturn's satellites.

00:02:04 It's not that hard.

00:02:06 We just have to find a way to adapt to a very thin atmosphere,

00:02:10 extreme temperatures, pressure, and a whole bunch of unpleasant things.

00:02:17 But let's hope.

00:02:19 In the end, it's just a matter of resources.

00:02:22 We'll need water, minerals, and other raw materials.

00:02:26 That way, we could create an autonomous colony.

00:02:29 And luckily, Ceres is a good place to do that.

00:02:32 We'd start by building homes in the craters.

00:02:36 We'd build domes to protect us from all kinds of danger, like radiation.

00:02:41 We'd also use the regolith of the asteroid belt.

00:02:46 The regolith, which is the part of the ground that covers the sea rock,

00:02:49 is a result of a cosmic alteration.

00:02:52 It's a bit like the surface layer of the lunar surface.

00:02:55 Why do we need it?

00:02:57 Because we could use it to 3D print foundations near the ice,

00:03:02 so that our bases are located near the water.

00:03:05 We'd then use these foundations to print other structures, like houses.

00:03:10 We'd also collect ice and organic molecules to create water.

00:03:16 And by combining water with regolith,

00:03:19 we'd get a ground in which to grow plants and food.

00:03:24 Wonderful!

00:03:26 There's also another option.

00:03:29 Create a colony underground,

00:03:31 that is, right next to the planet's icy crust.

00:03:35 If our science allows it,

00:03:39 we could accelerate Ceres' rotation.

00:03:42 It sounds crazy, but it would be very beneficial.

00:03:46 It would help us create artificial gravity in underground colonies.

00:03:51 Speaking of gravity,

00:03:55 all of this is very interesting,

00:03:57 but let's talk about the difficulties that await us during this colonization.

00:04:02 To settle on Ceres,

00:04:05 we'll have to face a number of challenges.

00:04:10 First, we'll have to develop a technology that will allow us to return to this planet.

00:04:15 We'll need vessels that can fly for long distances in the distant space.

00:04:20 To do this, we'll need to create a nuclear-thermal or electric propulsion technique,

00:04:26 and an extremely efficient type of fuel.

00:04:30 Then, we'll need a technology that can preserve life on this tiny rocky world,

00:04:36 that is, tools that can extract and use the available resources.

00:04:41 And since there's no atmosphere on Ceres,

00:04:44 we'll have to wear suits and live in pressurized habitats.

00:04:48 And that's just the beginning.

00:04:50 Living on this planet won't be easy.

00:04:54 For example, how to deal with extreme temperatures,

00:04:57 or radiation,

00:04:59 or the incredibly low gravity mentioned above.

00:05:03 This last point is certainly one of the biggest problems.

00:05:06 Ceres' gravity is only 3% of Earth's.

00:05:11 You wouldn't want to fly in space while playing football, would you?

00:05:15 But the fact that a simple bomb can lead you on an endless journey is not the only problem.

00:05:21 Even if you stay on the surface of the planet,

00:05:25 you'll encounter the same problems as astronauts from the International Space Station.

00:05:30 For example, muscle mass loss,

00:05:33 a decrease in bone density,

00:05:35 a vision loss,

00:05:37 a deterioration of the cardiovascular system.

00:05:40 Well, who would have thought that gravity was so important?

00:05:44 If we wanted to survive on Ceres,

00:05:47 we'd need either a bunch of doctors,

00:05:50 or artificial gravity.

00:05:52 And don't forget that this low gravity will also slow down our work.

00:05:59 Of course, we can't go anywhere without money.

00:06:03 Colonizing Ceres will cost a lot of money,

00:06:06 especially if you take into account everything that precedes it.

00:06:10 But Ceres is still one of the best candidates for colonization.

00:06:16 For example, there's a lot of methane and ammonia.

00:06:22 They can be transformed into fuel or gas azotes.

00:06:26 So why not use them to colonize Mars and Venus?

00:06:30 This low gravity has a few advantages.

00:06:36 Thanks to it, launching space vehicles would be much easier.

00:06:40 We'd waste a lot less fuel,

00:06:43 and travelling between Ceres and other planets would be a lot cheaper.

00:06:47 So, even if Ceres doesn't become our permanent residence,

00:06:52 it can become a good transport hub,

00:06:55 a kind of space station.

00:06:57 We could use it as a base to extract useful materials

00:07:02 from the asteroid belt.

00:07:04 Then we'd transport all that to Mars or Earth.

00:07:08 It could also become a supply station for ships

00:07:11 travelling beyond the solar system.

00:07:14 All this science fiction is pretty awesome, isn't it?

00:07:18 But I think that any attempt to create a permanent base

00:07:22 in the asteroid belt will have to wait.

00:07:25 Colonizing other planets is a difficult and complex task.

00:07:29 It will require the cooperation and expertise of many different people,

00:07:33 as well as the development of new technologies

00:07:36 and the resolution of many problems.

00:07:39 Before going to Ceres, we have to build infrastructure on the Moon,

00:07:44 on Mars, and somewhere in between.

00:07:47 Otherwise, the business will cost too much

00:07:50 and we will probably collapse before we even reach the dwarf planet.

00:07:54 But the more colonies we create,

00:07:58 the more chances we have of settling on Ceres one day.

00:08:01 This will not only open the asteroid belt to economic exploitation,

00:08:06 but will also serve as a springboard to the borders of the solar system.

00:08:11 The colonization of Jupiter's moons could follow.

00:08:16 In other words, the colonization of Ceres could bring in big profits.

00:08:20 Not only would it allow us to explore and understand this fascinating world,

00:08:24 but it could also provide us with precious resources

00:08:27 that would help us to continue exploring and colonizing the solar system.

00:08:32 Life on Ceres would be difficult, but exciting,

00:08:36 because humans would have a new home there to explore the mysteries of the universe.

00:08:42 Imagine all the new restaurants and shops we could have.

00:08:46 Welcome to Ceres Market, where everything is extraordinary.

00:08:50 If you like cosmic treasure hunting, Ceres is the right destination for you.

00:08:56 Just think about putting weights on your feet so you don't fly away.

00:09:01 It is normal for planets to be a little tilted to one side.

00:09:06 For example, the Earth is tilted at an angle of 23 degrees.

00:09:10 That's why we have seasons.

00:09:12 It's summer when the part of the world where you are is leaning closer to the sun,

00:09:17 and in reverse, it's winter when you move away.

00:09:20 But Uranus is more tilted than normal.

00:09:23 It rests at an angle of 98 degrees, which has a huge effect on its seasons.

00:09:28 Each season on Uranus lasts no less than 21 years.

00:09:32 Just think about it the next time you complain that winter lasts too long.

00:09:36 Here on Earth, we evaluate our journeys in minutes and hours, or even in days.

00:09:41 It takes 10 minutes to go to your best friend's house,

00:09:44 or 15 minutes to go to your favorite cafe.

00:09:46 But in space, it's different.

00:09:48 It's vast, which means we measure the distance that separates us from a certain point in years.

00:09:54 In most cases, such a distance is even expressed in light years.

00:09:59 If you wanted to go for a walk on the Moon one day,

00:10:02 it would take 9 years to cover the 380,000 kilometers that separate us.

00:10:07 Maybe you'd like to take a tour of our neighboring star, Proxima Centauri.

00:10:11 If you kept your foot on the ground at a constant speed of 110 km/h,

00:10:15 you would get there in 356 billion hours, or about 40.5 million years.

00:10:22 After the first 20 million years, you will probably wonder why you wanted to go there.

00:10:27 Mars is home to the largest valley we have ever discovered.

00:10:31 Valles Marineris.

00:10:33 It's a pretty impressive canyon system, 4,000 kilometers long,

00:10:37 which is five times larger than the Grand Canyon.

00:10:40 Researchers spotted it for the first time in the 1970s.

00:10:43 A volcano bank on the other side of the canyon ridge

00:10:47 probably helped form this valley.

00:10:50 We haven't yet discovered planets entirely made of diamonds,

00:10:54 but on some planets, precious stones do rain.

00:10:57 On Jupiter and Saturn, the gas giants of our solar system,

00:11:01 thunderstorms turn abundant methane into soot,

00:11:05 which we also know as carbon.

00:11:08 The soot falls and turns into graphite.

00:11:11 The graphite then turns into a diamond about 1 cm in diameter.

00:11:16 But before you start looking for a way to book a trip to collect diamonds,

00:11:20 know that these diamonds don't last.

00:11:22 After penetrating the core of the planet, they melt.

00:11:26 Have you ever noticed that when you observe the stars at night,

00:11:29 at the same time, let's say 9 p.m.,

00:11:32 they stay in the same place, but not the Moon?

00:11:35 There are two reasons for this.

00:11:37 First, it depends on the time you make your observations.

00:11:40 For example, if you look at it one evening at 9 p.m. and the next day at 11 p.m.,

00:11:45 you'll see the Moon in two quite different places.

00:11:48 In this case, even the stars will have different places in the sky

00:11:52 since our planet is rotating.

00:11:54 As you know, it takes it 24 hours to make a full tour.

00:11:58 This means that, from our point of view,

00:12:00 it seems that the sky and everything up there

00:12:03 move around us once every 24 hours.

00:12:07 In the same way, the Sun changes position, rises and sets every day.

00:12:12 So if you go out at night at the same time,

00:12:15 in most cases you'll have to wait an extra half hour, or even more,

00:12:19 for the Moon to find the same position as the previous night.

00:12:23 The stars are virtually immobile.

00:12:25 It looks like they're moving, but it's only because the Earth is rotating.

00:12:29 On the other hand, the Moon is really moving around our planet

00:12:33 and goes through different phases.

00:12:35 For example, the new Moon is the moment when it's completely black in the sky.

00:12:40 The full Moon is the moment when its illuminated side is totally turned towards the Earth.

00:12:44 It takes it about a month to make a complete tour of the Earth.

00:12:48 For your diamond collection,

00:12:50 you may have more chance on this planet,

00:12:53 which is 40 million light-years away from the Earth.

00:12:56 Scientists used to call it Super Earth.

00:12:59 A Super Earth is generally a planet much larger than ours.

00:13:03 This planet, for example, is twice the size of the Earth.

00:13:07 It's so close to its star that it makes a full tour in less than 18 hours,

00:13:11 which means that the year is rather short.

00:13:14 And since it's so close to its star,

00:13:16 its temperature goes up to 2,700 degrees Celsius.

00:13:20 Because of the heat combined with the planet's density,

00:13:23 scientists think its core is made up of carbon in the form of graphite and diamond.

00:13:28 More than 10 years ago, astronomers discovered a huge cloud of water vapor

00:13:33 12 billion light-years away from our planet.

00:13:36 This cloud is the largest water source we know of.

00:13:39 It's also the oldest.

00:13:41 It dates from a time when the universe was only 1.6 billion years old.

00:13:45 Today, it's 13.8 billion years old.

00:13:48 And yes, if you had opened a savings account 12 billion years ago,

00:13:52 with the interest in cash, you'd have a nice sum today.

00:13:56 But banks didn't exist at the time.

00:13:59 In short, this cloud is so large that it contains 140 billion times

00:14:03 the amount of water in all the oceans on our planet.

00:14:07 This cloud, in a way, feeds a black hole.

00:14:10 It could also contain enough gas, like carbon monoxide,

00:14:14 to encourage the black hole to become 6 times bigger than it is now.

00:14:19 The average temperature on our planet is about 14 degrees Celsius.

00:14:23 And the highest ever measured temperature was 57 degrees Celsius.

00:14:28 Does that seem hot to you?

00:14:30 Well, on Venus, it can reach 482 degrees Celsius,

00:14:34 which makes it the warmest planet in our solar system.

00:14:38 But it's not hot enough to melt steel.

00:14:41 It would take it to be higher than 1,400 degrees Celsius to get there.

00:14:45 But it's hot enough to melt lead.

00:14:48 And it's way too hot to live.

00:14:50 At least, in no way that we knew.

00:14:53 However, Venus is not the closest planet to the sun.

00:14:56 It's Mercury.

00:14:58 But it has a very thick atmosphere that traps greenhouse gases.

00:15:02 It's like you're covered in a very thick blanket in the middle of summer.

00:15:06 We're used to seeing volcanoes spitting hot lava in fusion.

00:15:10 After all, that's what they do mainly on Earth.

00:15:13 But in space, volcanoes tend to spit methane, water or ammonia.

00:15:19 And these materials freeze during the eruption,

00:15:21 and end up turning into frozen steam and something called volcanic snow.

00:15:26 They're called cryovolcanoes.

00:15:29 You can find them on the moons of Jupiter, Io and Europe,

00:15:33 on the moon of Saturn, Titan and Pluto.

00:15:36 These volcanoes are particularly active on Io, which has hundreds of chimneys.

00:15:41 NASA vehicles have even captured some of them in real-time eruptions.

00:15:46 The ice-freeze vapor that comes out of them extends over about 400 km.

00:15:51 In fact, we've just discovered another moon around Jupiter,

00:15:55 which could be adapted to agriculture one day.

00:15:58 It's called...

00:15:59 E-I-E-I-O!

00:16:01 Just kidding!

00:16:03 What happens to light after it disappears into a black hole?

00:16:08 A photon is a particle of light.

00:16:10 The event horizon is the limit of a black hole.

00:16:13 When an element, say a photon, crosses this limit, it can no longer escape.

00:16:18 But that doesn't mean the black hole has destroyed it.

00:16:21 It quickly attracts the photon to its centre,

00:16:23 where a huge mass is crammed into an infinitely small space.

00:16:27 But we don't know exactly what happens to photons in such extreme conditions.

00:16:31 It's still one of the biggest mysteries.

00:16:34 A black hole, does it destroy light or not?

00:16:37 Saturn has 82 moons that we know of,

00:16:40 53 confirmed and 29 others that are still on the waiting list

00:16:44 to be confirmed as real moons before they get their official names.

00:16:49 And one of these most amazing moons could be a large piece of rock

00:16:53 1,470 km in diameter called Iapetus.

00:16:58 It's dark on one side and bright on the other.

00:17:01 Its brightest half is 20 times brighter than the other.

00:17:05 The bright side is ice, the dark side is a bit more complicated.

00:17:10 One theory says it's dark because of particles from another moon, called Phebe.

00:17:16 Another theory says it could be because of heat.

00:17:20 As this moon rotates very slowly, its dark matter absorbs heat,

00:17:24 which makes it even darker.

00:17:26 In your opinion, what size can a black hole reach?

00:17:29 In theory, we can't find limits bigger than its mass.

00:17:33 But astronomers think that ultra-massive black holes, UMBH,

00:17:37 located in the heart of certain galaxies,

00:17:40 are usually up to 10 billion solar masses in size.

00:17:44 Recently, they even discovered that these UMBH

00:17:47 can't physically grow much bigger than that,

00:17:50 because in this case, they'd start to disrupt the accretion disks that feed them.

00:17:54 In doing so, they'd end up with a bigger eye than a bigger belly.

00:17:59 Most people imagine the color of the universe

00:18:02 as being somewhere between the Navy Blue and the pale turquoise.

00:18:05 Even some researchers thought it was the case.

00:18:08 But we managed to determine the cosmic color

00:18:10 by combining the light of more than 200,000 galaxies

00:18:13 located less than 2 billion light years away from our planet.

00:18:17 The real color is actually closer to beige.

00:18:20 The researchers were wrong, because the software wasn't properly calibrated.

00:18:24 They finally converted the cosmic spectrum

00:18:26 into the color our eyes would see if we were exposed to it.

00:18:29 The team defined this color as a cosmic latte,

00:18:32 without sugar, and air-conditioned, please.

00:18:35 Venus was most likely covered by an ocean

00:18:39 with a depth of 10 to 300 meters.

00:18:42 In addition, a certain amount of water was trapped in the planet's soil.

00:18:46 The water had stable temperatures of 20 to 50 degrees Celsius,

00:18:51 which was quite tolerable and not so different from the current Earth's temperatures.

00:18:56 In short, for 3 billion years,

00:18:59 until something unthinkable happened 700 million years ago,

00:19:04 Venus could have been habitable.

00:19:06 But today, it's not.

00:19:08 The Moon is the second brightest object in our sky.

00:19:12 Yet, among the other astronomical bodies,

00:19:15 it's one of the darkest and least reflective.

00:19:17 But our natural satellite seems bright because it's very close to us.

00:19:21 In the same way, our planet seems much brighter

00:19:24 when you look at it from space.

00:19:26 It's because clouds, ice and snow reflect much more light than most rocks.

00:19:32 Triton, Neptune's moon, has its entire surface covered with several layers of ice.

00:19:37 If this satellite replaced our current moon,

00:19:39 the night sky would be seven times brighter.

00:19:44 Neutron stars are among the smallest and most massive objects in space.

00:19:48 They are generally about 18 km in diameter,

00:19:51 but they are several times heavier than the Sun.

00:19:53 And they rotate around 600 times per second,

00:19:57 much faster than a professional skater.

00:19:59 Saturn is the planet with the least density in the Solar System.

00:20:04 Its density is equivalent to one eighth of that of Earth.

00:20:07 And yet, because of its immense volume,

00:20:10 the planet is 95 times more massive than Earth.

00:20:13 The transitory lunar phenomenon is one of the most enigmatic things that happens on the Moon.

00:20:19 It's an ephemeral change of light, color or other, on the surface of the satellite.

00:20:24 Most often, it's random light flashes.

00:20:27 Astronomers have been observing this phenomenon since the 1950s.

00:20:31 They noticed that flashes were happening in an unpredictable way.

00:20:34 Sometimes, they can happen several times a week.

00:20:37 Then, they disappear for several months.

00:20:40 Some of them don't last more than a few minutes.

00:20:42 But some of them last several hours.

00:20:44 In 1969, one day before Apollo 11 landed on the Moon,

00:20:50 one of the mission members noticed that part of the lunar surface was brighter than the surrounding landscape.

00:20:56 It was said that this area had a kind of fluorescence.

00:21:00 Unfortunately, we still don't know if this phenomenon was linked to the mysterious lunar flash.

00:21:05 Waste is not only a problem in the oceans, cities and forests of the Earth.

00:21:10 There are also what we call "spatial waste".

00:21:13 It's any object made by man that has been left in space and is useless.

00:21:18 There are also natural debris from meteorites and other cosmic objects.

00:21:22 There are currently more than 500,000 spatial debris orbiting the Earth,

00:21:27 at speeds high enough to cause significant damage if they collide with a space ship or a satellite.

00:21:33 NASA does its best to track each object

00:21:36 to ensure that missions outside the Earth can reach their destination safely.

00:21:41 Our Sun is incredibly massive.

00:21:44 For proof, 99.86% of the entire mass of the Solar System consists of the mass of the Sun,

00:21:50 in particular the hydrogen and helium it is composed of.

00:21:53 The remaining 0.14% are mainly the mass of the eight planets of the Solar System.

00:21:59 The atmosphere of the Sun is warmer than its surface.

00:22:03 The surface temperature reaches 5,500 °C, but the high atmosphere reaches millions of degrees.

00:22:10 If we could dig a tunnel directly in the center of the planet and go out the other way,

00:22:15 and you were adventurous enough to jump in, it would take you 42 minutes to cross it.

00:22:21 You would accelerate as you fell to reach the maximum speed when you reached the core of the Earth.

00:22:28 After half the journey, you would then fall up more and more slowly.

00:22:33 When you reached the opposite surface, your speed would be back to zero.

00:22:37 Unless you manage to get out of the hole, you would immediately start falling again,

00:22:41 to go down, or go up, to the other side of the planet.

00:22:45 This journey would last an eternity, and this because of the bizarre effects of gravity.

00:22:54 There could be more metals, for example titanium or iron, in the lunar craters than astronomers thought.

00:23:00 The biggest problem with this discovery?

00:23:02 It contradicts the main theory about how the Moon was formed.

00:23:06 This theory states that the natural satellite of the Earth detached itself from our planet

00:23:11 after a collision with a massive space object.

00:23:14 But then, why does the Earth's crust, poor in metals,

00:23:17 contains much less iron oxide than the Moon's?

00:23:20 This could mean that the Moon was formed from materials much deeper inside our planet.

00:23:26 Or these metals could have appeared when the lunar surface, in fusion, cooled slowly.

00:23:32 Or maybe, as we've been saying for centuries, it's made of cheese.

00:23:36 The Earth could have been purple before it became blue and green.

00:23:40 A scientist has a theory that a substance existed in the ancient microbes before chlorophyll,

00:23:46 this thing that makes plants green, evolved on Earth.

00:23:49 This substance reflected the sunlight in red and mauve,

00:23:53 colors that combined to give purple.

00:23:55 If it's true, the young Earth may have fed on strange purple plants

00:23:59 before all these green things appeared.

00:24:02 The highest mountain in the solar system is Olympus Mons on Mars.

00:24:06 It is three times higher than Mount Everest, the highest peak on Earth compared to the sea level.

00:24:12 If you stood at the top of Olympus Mons, you wouldn't understand that you were on a mountain.

00:24:16 These slopes would be hidden by the curvature of the planet.

00:24:20 Astronomers have found a huge water reservoir in space, the largest ever detected.

00:24:25 It's a shame that it's also the furthest.

00:24:27 It's 12 billion light years away from us.

00:24:30 This water vapor cloud contains 140 billion times more water than all the oceans of the Earth combined.

00:24:37 Venus rotates at its own pace, without rushing.

00:24:41 A complete rotation takes 243 terrestrial days.

00:24:44 And the planet needs a little less than 225 terrestrial days to complete the sun's rotation.

00:24:50 This means that one day on Venus is longer than a year.

00:24:54 There is very little seismic activity inside the Moon.

00:24:57 However, mini lunar earthquakes, caused by the gravitational force of our planet,

00:25:02 sometimes occur several kilometers below the surface.

00:25:06 Then, tiny cracks and fractures appear on the surface of the satellite, and gases escape.

00:25:12 Mars is the last of the four inner planets, also called "telluric" because they are made up of rocks and metals.

00:25:19 The red planet has a core made up mainly of iron, nickel and sulfur.

00:25:24 It measures between 1,500 and 1,900 kilometers in diameter.

00:25:28 But this core doesn't move.

00:25:29 That's why Mars doesn't have a magnetic field on the planet's scale.

00:25:33 The weak magnetic field it has is only one hundredth of that of the Earth.

00:25:38 When the planets of the solar system began to form, the Earth didn't have a moon for a very long time.

00:25:44 It took 100 million years for our natural satellite to appear.

00:25:49 There are several theories about how the Moon appeared.

00:25:52 But the one that prevails is the fission theory.

00:25:56 It states that the Moon formed when an object collided with the Earth,

00:26:01 seeing particles in all directions.

00:26:06 Gravity brought the particles together and the Moon was created.

00:26:10 It ended up landing on the Earth's ecliptic plane, which is the current trajectory of the Moon.

00:26:16 The largest living being on Earth is a mushroom in Oregon.

00:26:21 This huge mushroom, Armillaria, lives in the National Forest of Malheur and covers an area of 9.5 square kilometers.

00:26:29 It could be up to 8,500 years old.

00:26:32 But we can forgive you for missing it, because it is largely hidden underground.

00:26:37 When the individual roots of Armillaria meet, they can fuse to become one mushroom,

00:26:44 which explains how it became so big.

00:26:47 If you could put all these mushrooms together in one big ball, it could weigh up to 35,000 tons.

00:26:53 It's about as heavy as 200 gray whales.

00:26:58 The largest asteroid in the Solar System is called Vesta, and it is so big that it is sometimes called a dwarf planet.

00:27:05 A trip to the second closest star to us, after the Sun, would take you 5 million years in a straight-line plane.

00:27:11 It's what we call an ultra-long-haul flight.

00:27:14 Space is not supposed to be black. There are stars everywhere.

00:27:18 Shouldn't it light up everything around it?

00:27:21 In reality, we don't see stars everywhere, because some of them haven't existed for a long time for their light to reach Earth.

00:27:28 A day on Uranus lasts 17 hours, 14 minutes and 24 seconds.

00:27:33 But the planet has an inclination of about 98 degrees.

00:27:37 And that makes a season on the gas giant last 21 terrestrial years.

00:27:42 Some scientists think that our planet once had an additional satellite.

00:27:47 According to their research, a smaller celestial body, about 1,100 km wide, was orbiting the Earth like a second moon.

00:27:54 It most likely crashed on our main satellite later.

00:27:58 Such a collision could explain why the two sides of the Moon look so different from each other, the Moon being strongly cratered and rugged.

00:28:06 It is normal that planets are a little inclined to one side.

00:28:11 For example, the Earth is tilted at an angle of 23 degrees.

00:28:15 That's why we have seasons.

00:28:17 It's summer when the part of the world where you are is leaning closer to the sun.

00:28:22 And vice versa, it's winter when you move away.

00:28:25 But Uranus is more inclined than normal.

00:28:28 It rests at an angle of 98 degrees, which has a huge effect on its seasons.

00:28:34 Each season on Uranus lasts no less than 21 years.

00:28:37 Think about it the next time you complain that winter lasts too long.

00:28:41 Here on Earth, we evaluate our journeys in minutes and hours, or even in days.

00:28:46 It takes 10 minutes to go and trap your best friend, or 15 minutes to go to your favorite cafe.

00:28:51 But in space, it's different.

00:28:54 It's vast, which means that we measure the distance that separates us from a certain point in years.

00:28:59 In most cases, such a distance is even expressed in light years.

00:29:04 If you wanted to go for a walk on the Moon one day, it would take you 9 years to cover the 380,000 km that separate us.

00:29:12 Maybe you'd like to take a tour of our neighboring star, Proxima Centauri.

00:29:16 If you kept your foot on the ground at a constant speed of 110 km/h, you would get there in 356 billion hours,

00:29:24 which is about 40.5 million years.

00:29:27 After the first 20 million years, you will probably wonder why you wanted to go there.

00:29:32 Mars is home to the largest valley we have ever discovered, Valles Marineris.

00:29:38 It's a pretty impressive canyon system, 4,000 km long, which is five times larger than the Grand Canyon.

00:29:45 Researchers first spotted it in the 1970s.

00:29:48 A volcano bank on the other side of the canyon ridge probably helped form this valley.

00:29:55 We haven't yet discovered planets entirely made of diamonds,

00:29:59 but on some planets, precious stones do rain.

00:30:02 On Jupiter and Saturn, the gas giants of our solar system,

00:30:07 thunderstorms turn abundant methane into soot, which we also know as carbon.

00:30:13 The soot falls and turns into graphite.

00:30:16 The graphite then turns into a diamond about 1 cm in diameter.

00:30:21 But before you start looking for a way to book a trip to collect diamonds,

00:30:25 know that these diamonds don't last. After penetrating the core of the planet, they melt.

00:30:31 Have you ever noticed that when you look at the stars overnight at the same time,

00:30:35 let's say at 9 p.m., they stay in the same place, but not the Moon?

00:30:40 There are two reasons for this.

00:30:42 First, it depends on the time you make your observations.

00:30:46 For example, if you look at it one evening at 9 p.m. and the next day at 11 p.m.,

00:30:50 you will see the Moon in two quite different places.

00:30:53 In this case, even the stars will have different places in the sky,

00:30:57 since our planet is rotating.

00:30:59 As you know, it takes it 24 hours to make a full tour.

00:31:03 This means that, from our point of view, it seems that the sky and everything up there

00:31:08 move around us once every 24 hours.

00:31:12 In the same way, the Sun changes position, rises and sets every day.

00:31:17 So if you go out overnight at the same time,

00:31:20 in most cases you will have to wait an additional half hour, or even more,

00:31:25 for the Moon to find the same position as the previous night.

00:31:29 The stars are practically immobile.

00:31:31 It looks like they are moving, but it's only because the Earth is rotating.

00:31:35 On the other hand, the Moon is really moving around our planet

00:31:39 and goes through different phases.

00:31:41 For example, the new Moon is the moment when it is completely black in the sky.

00:31:45 The full Moon is the moment when its illuminated side is completely turned towards the Earth.

00:31:50 It takes it about a month to make a full tour of the Earth.

00:31:54 For your diamond collection, you may have more chance on this planet,

00:31:58 located 40 million light years from the Earth.

00:32:01 Scientists used to call it Super Earth.

00:32:04 A Super Earth is generally a planet much larger than ours.

00:32:08 This planet, for example, is twice the size of the Earth.

00:32:12 It is so close to its star that it makes a full tour in less than 18 hours,

00:32:16 which means that the year is rather short.

00:32:19 And since it is so close to its star, its temperature rises to 2700 ° C.

00:32:25 Because of the heat combined with the density of the planet,

00:32:28 scientists think that its core is made up of carbon in the form of graphite and diamond.

00:32:34 More than 10 years ago, astronomers discovered a huge cloud of water vapor

00:32:38 12 billion light years from our planet.

00:32:41 This cloud is the largest water source we know of.

00:32:44 It is also the oldest.

00:32:46 It dates from the time when the universe was only 1.6 billion years old.

00:32:50 Today, it is 13.8 billion years old.

00:32:53 And yes, if you had opened a savings account 12 billion years ago,

00:32:57 with interest in the stock market, you would have a nice sum today.

00:33:01 But banks did not exist at the time.

00:33:04 In short, this cloud is so large that it contains 140 billion times the amount of water

00:33:09 in all the oceans of our planet.

00:33:12 This cloud somehow feeds a black hole.

00:33:15 It could also contain enough gas, like carbon monoxide,

00:33:19 to encourage the black hole to become 6 times larger than it is currently.

00:33:24 The average temperature of our planet is about 14 ° C,

00:33:28 and the highest temperature ever measured was 57 ° C.

00:33:33 Does it seem hot to you? Well, on Venus, it can reach 482 ° C,

00:33:39 which makes it the warmest planet in our solar system.

00:33:43 But it is not hot enough to melt steel.

00:33:46 It would take it to be higher than 1,400 ° C to get there.

00:33:50 But it's hot enough to melt lead, and it's way too hot to keep life,

00:33:55 at least in any way we knew.

00:33:58 Venus is not the closest planet to the sun, it is Mercury,

00:34:03 but it has a very thick atmosphere that traps greenhouse gases.

00:34:07 It's like you're covered in a very thick blanket in the middle of summer.

00:34:11 We are used to seeing volcanoes spit hot lava in fusion.

00:34:15 After all, that's what they do mainly on Earth.

00:34:18 But in space, volcanoes tend to spit methane, water or ammonia.

00:34:24 And these materials freeze during the eruption and end up turning into frozen steam

00:34:29 and something called volcanic snow.

00:34:32 They are called cryovolcanoes.

00:34:35 You can find them on the moons of Jupiter, Io and Europe,

00:34:38 on the moon of Saturn, Titan and Pluto.

00:34:42 These volcanoes are particularly active on Io, which has hundreds of chimneys.

00:34:47 NASA vehicles have even captured some of them in real-time eruptions.

00:34:52 The frozen steam that comes out of them extends for about 400 km.

00:34:57 In fact, we have just discovered another moon around Jupiter

00:35:01 that could be adapted to agriculture one day.

00:35:04 It's called Iaiaio.

00:35:06 Ha ha, I'm kidding.

00:35:08 What happens to the light exactly after it disappears into a black hole?

00:35:13 The photon is a particle of light.

00:35:16 The horizon of events is the limit of a black hole.

00:35:19 When an element, let's say a photon, crosses this limit, it can no longer escape.

00:35:24 But that doesn't mean that the black hole destroys it.

00:35:27 It quickly attracts the photon to its center,

00:35:29 where a huge mass is crammed into an infinitely small space.

00:35:33 But we don't know exactly what happens to photons in such extreme conditions.

00:35:37 It's still one of the biggest mysteries.

00:35:40 A black hole, does it destroy the light or not?

00:35:43 Saturn has 82 moons that we know of,

00:35:46 53 confirmed and 29 others that are still on the waiting list

00:35:50 to be confirmed as real moons before obtaining their official name.

00:35:55 And one of these most amazing moons could be a large piece of rock

00:35:59 1,470 km in diameter called Iapetus.

00:36:03 It is dark on one side and bright on the other.

00:36:06 Its brightest half is 20 times more reflective than the other.

00:36:10 It turns out that the bright side is ice.

00:36:13 The dark side is a little more complicated.

00:36:16 One theory claims that it is dark because of particles

00:36:19 from another moon called Phebe.

00:36:22 Another theory says that this could be because of the heat.

00:36:25 As this moon rotates very slowly, its dark matter absorbs heat,

00:36:30 which makes it even darker.

00:36:32 In your opinion, what size can a black hole reach?

00:36:35 In theory, we cannot find limits greater than its mass.

00:36:39 But astronomers think that ultra-massive black holes, UMBH,

00:36:43 located in the heart of certain galaxies,

00:36:46 are usually up to 10 billion solar masses in size.

00:36:50 Recently, they even discovered that these UMBH

00:36:53 cannot physically grow much larger than that,

00:36:56 because in this case, they would begin to disturb the accretion discs that feed them.

00:37:00 In doing so, they would somehow end up having a bigger eye than the belly.

00:37:05 Most people imagine the color of the universe as being somewhere

00:37:08 between the Navy Blue and the pale turquoise.

00:37:11 Even some researchers thought it was the case.

00:37:14 But we managed to determine the cosmic color by combining the light

00:37:17 of more than 200,000 galaxies, located less than 2 billion light years away from our planet.

00:37:22 The real color is actually closer to beige.

00:37:25 Researchers were wrong because the software was not properly calibrated.

00:37:29 It finally converted the cosmic spectrum into the color

00:37:32 that our eyes would see if we were exposed to it.

00:37:35 The team defined this color as a cosmic latte,

00:37:38 without sugar, and with a "please".

00:38:00 The heat of the sun is under our feet.

00:38:03 Scientists have discovered that the core of the Earth is actually as hot as the surface of the sun,

00:38:08 about 6,000 degrees Celsius.

00:38:11 One of the reasons why it is so hot below is that the Earth still loses heat

00:38:16 from its creation billions of years ago.

00:38:20 In addition, when an object as big as Mars hit the young Earth,

00:38:24 it not only created the Moon, according to a theory,

00:38:27 but it also melted the surface of the planet.

00:38:30 Much of this additional heat is probably still stored inside the core.

00:38:36 But there is no need to worry.

00:38:39 It is more difficult for us to access the core of the planet than to probe the surface of Pluto.

00:38:44 In fact, there is a good chance that we will never develop a technology

00:38:48 that will allow us to physically reach the core.

00:38:51 There is no air on the Moon.

00:38:54 But how can there be rust?

00:38:57 Scientists have discovered the presence of hematite on the Moon, which is a kind of rust.

00:39:01 A NASA special research instrument examined the light reflected by the surface of the Moon.

00:39:07 It turned out that the composition of the poles of our natural satellite

00:39:11 was very different from the rest of the Moon.

00:39:14 The surface is sprinkled with rocks rich in iron.

00:39:17 But without oxygen or liquids, rust cannot appear.

00:39:21 Solar winds add to the mystery.

00:39:24 They bombard the Moon with hydrogen.

00:39:26 But hydrogen makes the formation of hematite much more difficult.

00:39:30 Even if the Moon has no atmosphere, it still has traces of oxygen.

00:39:34 Its source is the high atmosphere of our planet.

00:39:37 The Earth also protects the Moon from almost 100% of the solar winds, but not all the time.

00:39:42 And even if our natural satellite is completely dry,

00:39:45 there could be ice in the shady craters of its hidden face.

00:39:51 A day on Uranus lasts 17 hours, 14 minutes and 24 seconds.

00:39:56 But the planet has an inclination of about 98 degrees.

00:40:00 And that means that a season on the gas giant lasts 21 terrestrial years.

00:40:06 Mars has two moons, Phobos and Deimos.

00:40:10 In the 30 to 50 million years to come,

00:40:13 the gravitational forces of Mars will tear Phobos,

00:40:16 and this will probably lead to the formation of a ring around the planet.

00:40:22 The Earth is the densest planet in the solar system.

00:40:25 In the centre of the Earth, the core occupies 15% of the planet's volume.

00:40:29 It is made up of two parts, the external core and the internal core.

00:40:34 The internal core is a solid ball made up of iron and nickel.

00:40:38 Its radius is 1220 km, which represents 20% of the Earth's radius,

00:40:44 and 80% of the Moon's radius.

00:40:47 The external core, 2,400 km thick, is liquid.

00:40:51 It is also made up of iron and nickel, but it is not strong enough to be solid.

00:40:59 Mars houses the largest volcano in the solar system.

00:41:02 Although everything seems calm on Mars nowadays,

00:41:05 in the past, a kind of force caused the formation and eruption of huge volcanoes.

00:41:11 One of these volcanoes is Olympus Mons.

00:41:13 It is 26 km high, which is three times the height of Everest,

00:41:17 and 600 km wide, which is the size of Arizona.

00:41:21 The volcano has reached such a size because of the low gravity on Mars

00:41:26 and the lack of movement of the tectonic plates.

00:41:30 Gravity is not the same everywhere.

00:41:33 The rocks, metals and other minerals and substances that make up the planet

00:41:37 are tighter in the ground in some places than in others.

00:41:40 This has surprising consequences.

00:41:42 Gravity varies slightly depending on where you are.

00:41:45 You weigh 0.5% less at the equator than at the poles.

00:41:49 In most cases, this represents a difference of less than a kilo.

00:41:53 The altitude at which you are also has an effect.

00:41:56 So if you were at the top of Mount Everest, you would also weigh slightly less.

00:42:01 The most resilient living being on Earth is so small that you can't see it.

00:42:06 Tardigrades, also known as water bears,

00:42:09 are cute little creatures with eight legs and crushed heads

00:42:13 that are less than a hundredth of a centimeter.

00:42:16 Despite their microscopic size, they can survive almost anywhere.

00:42:20 They prefer damp moss or the bottom of lakes,

00:42:23 but they won't complain if you put them in a really uncomfortable place.

00:42:27 They can withstand extreme cold and incredible heat

00:42:31 and survive under enormous pressure and high radiation.

00:42:34 Some of these bears have even managed to survive without protection in space for 10 days.

00:42:40 They manage all this by rolling in balls and hibernating,

00:42:43 which reduces their need for oxygen and food.

00:42:47 The gravity of the Moon is about 17% of that of the Earth.

00:42:51 If you weighed 91 kilos on our planet, your lunar weight would only go to 15 kilos.

00:42:56 You could also carry objects six times heavier than what you can carry on Earth.

00:43:01 It would also be easier to walk on the surface of the Moon, but it would also be more dangerous.

00:43:06 Your feet, inside a heavy space suit, would sink into the lunar soil up to 15 centimeters deep.

00:43:13 But let's imagine that you decide to avoid the tedious process of walking by jumping into the air.

00:43:18 You would probably lose control of your jumps in no time.

00:43:22 In addition, the surface of the Moon is full of deep craters.

00:43:26 Avoiding them all would be a feat.

00:43:29 You can see solar eclipses, because even though the Moon is 400 times smaller than the Sun,

00:43:34 it is also 400 times closer to the Earth.

00:43:37 It is therefore perfectly capable of obscuring our star.

00:43:40 But in 50 million years, the Moon will no longer be able to completely block the Sun

00:43:45 because of its changing orbit.

00:43:48 A complete space suit from NASA costs a staggering $12 million,

00:43:53 70% of which is dedicated to the command module and the backpack.

00:43:58 In the very center of Uranus, there is a relatively small rocky core,

00:44:03 just half the mass of the Earth.

00:44:05 Compared to other planets, the core of Uranus is rather cold, 5000 degrees Celsius.

00:44:11 An ice cape surrounds the solid core, and it represents the largest part of the planet, about 80%.

00:44:17 But it is not the ice you might think of.

00:44:20 It is a hot and dense fluid made up of water, ammonia and methane,

00:44:25 sometimes called the ocean of water and ammonia.

00:44:28 The atmosphere of Uranus is mainly composed of hydrogen and helium,

00:44:33 but it has this blue-green hue because of the methane gas that absorbs red light.

00:44:38 The ocean on Jupiter is larger than all the others in the solar system,

00:44:42 but unlike all the oceans on Earth, it is not made of water but of metallic hydrogen.

00:44:47 The depth of this ocean is staggering, 40,000 km,

00:44:51 almost as much as the circumference of the Earth.

00:44:55 Venus is a champion in volcanic matter.

00:44:58 It has about 1,600, but none of them is known to erupt.

00:45:03 There is a supermassive black hole 250 million light-years away from us.

00:45:08 It emits the deepest sound ever detected for an object in the universe.

00:45:12 It is 57 octaves lower than the central back of your piano.

00:45:16 It is a quadrillion times deeper than what we can hear.

00:45:20 Mercury is a few billion years old.

00:45:25 In 2016, scientists discovered anomalies on the surface of the planet that show that it is shrinking.

00:45:31 After further research, they discovered that Mercury had not yet finished cooling.

00:45:37 There are planets that are not linked to any stellar orbit and that orbit in space without a goal.

00:45:43 Among the most spectacular space objects are pulsars.

00:45:47 Pulsars are a type of neutron star.

00:45:50 They expel a part of their matter almost at the speed of light.

00:45:54 Regular pulsars rotate at a reasonable speed of 1/10 to 60 times per second.

00:46:00 But millisecond pulsars can rotate at an impressive speed of 700 times per second,

00:46:06 which is far too fast for the human eye to detect.

00:46:10 When they rotate, they emit a radiation beam from their axis that looks like the light of a lighthouse.

00:46:17 Astronomers can notice pulsars when they face the Earth,

00:46:21 because it looks like a light is shining on our planet.

00:46:24 When the light shines elsewhere, the pulsar cannot be seen.

00:46:29 Our sun is incredibly massive.

00:46:32 Do you want proof?

00:46:34 99.86% of the entire mass of the solar system is the mass of the sun,

00:46:39 composed in particular of hydrogen and helium.

00:46:42 The remaining 0.14% is mainly the mass of the eight planets in the solar system.

00:46:48 Saturn's rings are very thin compared to its size.

00:46:54 If you had a reduced model of the planet 1 meter wide,

00:46:58 the rings would be 10,000 times thinner than a razor blade.

00:47:02 Even though Venus is the warmest planet in our solar system, it still has snow.

00:47:07 But not the snow you expect.

00:47:10 It snows metals and it rains acid.

00:47:13 Not really the ideal place for your next vacation.

00:47:16 Imagine a basketball ball spinning on your finger.

00:47:22 A point near the middle of the ball will take more time to return to its starting point

00:47:27 than the precise point where your finger is.

00:47:29 The Earth spins about the same way.

00:47:31 People who live in central Africa spin at 1,600 km/h while the planet spins,

00:47:36 while those in the South Pole do not really move, unless they turn on the spot.

00:47:41 At the same time, we all move through space at the same speed,

00:47:45 because the planet also spins around the sun at 108,000 km/h.

00:47:51 The temperature at the limit of the internal and external core of our planet is 6,000 °C.

00:47:57 It's as hot as the surface of the sun,

00:47:59 and the pressure that reigns there is 3.3 million times higher than the atmospheric pressure at sea level.

00:48:05 Two or three years ago, an asteroid was attracted to the Earth's orbit and began to spin around the planet.

00:48:12 Even if it's not bigger than a car, it's still an event.

00:48:16 Of the more than a million asteroids known to astronomers,

00:48:20 only the second has spun around our planet.

00:48:23 Called 2020 CD3, it's our temporary mini-moon,

00:48:27 but it won't stay with the Earth for long.

00:48:30 The asteroid follows a random orbit and moves away slowly.

00:48:34 Temporary objects, like 2020 CD3, are rare.

00:48:39 They must have a specific direction and speed to be captured by the Earth's gravitational attraction.

00:48:45 Otherwise, they crash on the planet or fly in another direction.

00:48:49 The movement of galaxies and amas located billions of light years away from us

00:48:54 suggests that there is an extremely massive body outside the visible universe.

00:48:59 In billions of years, the expansion of the universe will make space so dense

00:49:04 that we will no longer be able to see the stars in the sky.

00:49:07 The Moon is not a perfect sphere. It has the shape of an egg.

00:49:12 In addition, the center of gravity of our satellite is located a little over 1 km from its geometric center.

00:49:18 Even though Venus is the warmest planet in our solar system, it still has snow.

00:49:23 But not the snow we think of.

00:49:26 It snows metals and it rains acid.

00:49:28 Not really the ideal place for your next vacation.

00:49:31 Saturn is mainly composed of hydrogen and helium,

00:49:35 with a few traces of methane, ammonia and water.

00:49:38 But it contains more sulfur than Jupiter, which gives the planet an orange hue similar to that of smog.

00:49:44 On Earth, sound waves make air molecules vibrate.

00:49:48 That's why we can hear sounds.

00:49:51 Other planets and moons also allow sound to travel through environments such as their atmospheres and oceans.

00:49:57 In space, however, it is said that there is no sound,

00:50:00 because there are no molecules to vibrate and emit sound waves.

00:50:04 However, all researchers do not agree on this point,

00:50:07 since space is not just an empty space devoid of everything.

00:50:10 Between the void, there are gas clouds and other parasitic particles.

00:50:14 So, depending on where you are, sound waves can be possible.

00:50:19 Astronomers know with certainty that the universe is growing,

00:50:24 and the speed at which it is growing is constantly increasing.

00:50:27 But if the whole thing is growing, there must be some kind of edge, right?

00:50:34 It is unlikely that people will ever discover it.

00:50:37 But if it is, then what would it be?

00:50:39 A huge brick wall and nothing else?

00:50:42 An abyss that leads nowhere?

00:50:44 The most common theory is that the universe is shaped in such a way that it cannot have edges.

00:50:50 But this is not the only hypothesis.

00:50:52 Another theory is even more difficult to understand.

00:50:55 The universe is infinite.

00:50:58 And our part of it is not that unique.

00:51:01 This means that somewhere over there, there is another roof, or rather, other versions of roofs.

00:51:07 One of them is just a little smaller.

00:51:09 The other has a different hairstyle.

00:51:11 The third is identical to you in every way possible.

00:51:15 There is also a theory about a multi-universe, which is made up of many smaller universes.

00:51:21 And the universe in which we live is only a tiny bubble among other similar bubbles.

00:51:27 Scientists who support this idea are also certain that bubble universes can come into contact with each other.

00:51:34 Gravity then begins to circulate between them.

00:51:37 And when two or three universes connect, a big bang occurs.

00:51:41 Just like the one that created our universe.

00:51:44 Neptune is the most windy place in the solar system.

00:51:47 Ice-cold methane clouds are whipping on the planet at a speed of 1900 km/h.

00:51:53 The core of Neptune is solid and is mainly composed of iron and a few other metals.

00:51:58 Its mass is 1.2 times greater than that of Earth.

00:52:02 The temperature inside reaches 5000 ° C.

00:52:06 Astronomers also think that at a depth of 7000 km,

00:52:10 there could be a layer of diamonds where it rains diamond crystals.

00:52:15 On Earth, people are used to a magnificent sunset in shades of orange, red and yellow.

00:52:22 But on Mars, the sky, normally pinkish red, turns blue when the sun sets below the horizon.

00:52:28 This is because Mars is much further from the sun than Earth,

00:52:32 which makes the sunlight less intense.

00:52:35 The fine dust of the Martian atmosphere absorbs the blue light and gets rid of the warmer colors that you usually see on Earth.

00:52:42 But whether it's blue or yellow, sunsets are always spectacular.

00:52:47 With about a quarter of the size of Earth, the Moon is rather huge compared to other satellites in space.

00:52:54 There is nothing comparable to this situation elsewhere in the solar system.

00:52:58 Pluto has a moon that is almost twice as big as it, but it's more of a twin than a satellite.

00:53:04 There are more than 150 moons in our solar system, and Earth's is the fifth largest of all.

00:53:11 There could be a labyrinth of lava tubes on the Moon.

00:53:15 Not long ago, astronomers studied the results of an underground lunar topography.

00:53:20 They discovered a massive cave under the surface of the satellite.

00:53:24 About 50 km long and 100 km wide, the cave is probably the result of a volcanic activity 3 billion years old.

00:53:32 After hardening, the lava currents created a thick hard crust outside.

00:53:37 But inside, the lava continued to flow, melting the rock and forming tunnels and caves.

00:53:43 The countless pits on the surface of the Moon discovered by NASA could be the openings of these lava tubes.

00:53:49 We cannot deter the majority of the Earth's gold.

00:53:52 99% of this gold ended up in the center of the planet several billion years ago, attracted by the iron of the Earth's core.

00:53:59 We're talking about 1.6 quadrillion tons of gold.

00:54:03 That's enough to cover the entire surface of the planet with 50 cm of gold.

00:54:08 And if all these meteorites hadn't crashed on the ground by bringing in additional amounts of gold, they would be even rarer.

00:54:16 Not long ago, astronomers discovered a huge blob of a mysterious substance.

00:54:21 It was hidden under the surface of the Moon's hidden face.

00:54:25 Its mass was the same as that of a pile of metal five times larger than the Great Hawaii Island.

00:54:31 The enigmatic object is located 300 km away under a huge crater that appeared on the surface of the Moon billions of years ago.

00:54:40 The blob probably has something to do with a super collision.

00:54:44 It could be the metal core of the object that hit the Moon at the time.

00:54:48 Scientists are eager to get their hands on this discovery.

00:54:52 It could explain a lot of things about the South Pole basin of Aitken, the largest known in the solar system.

00:54:58 If it were on Earth, it would extend from Washington to Texas.

00:55:03 In 2011, astronomers discovered a huge reservoir of water floating simply in space around a supermassive black hole called Kazar.

00:55:12 Floating water vapors have been found throughout the universe, but they are not that common.

00:55:17 This particular reservoir contains about 140 trillion times the amount of water contained in the oceans of the Earth.

00:55:24 It is one of the oldest, largest and, with more than 12 billion light years, one of the most distant things known to humanity.

00:55:33 In space, astronauts can lose about 1% of their muscle mass every month.

00:55:39 To avoid this, they must exercise two hours a day.

00:55:43 The Milky Way and the Andromeda Galaxy will meet in 3.75 billion years.

00:55:50 They move from one to the other at a dizzying speed.

00:55:54 When the two galaxies collide, they will form a huge elliptical galaxy.

00:56:01 Have you ever looked at the night sky and tried to count all the stars?

00:56:05 Good luck!

00:56:06 Our galaxy, the Milky Way, has about 100 billion stars.

00:56:11 But other estimates say this figure is more than 200 billion.

00:56:14 Because calculating the exact amount is an almost impossible task, even for astronomers.

00:56:20 As for the entire universe, it has at least one billion trillion stars,

00:56:24 that is, a 1 with 21 zeros behind.

00:56:27 For comparison, this means that there are more stars in space than there are grains of sand on all the beaches of the Earth.

00:56:41 640 light years away from the Sun, scientists discovered the planet WASP-76b,

00:56:49 on which it rains iron.

00:56:51 The planet is very close to its star and always faces it on the same side.

00:56:56 We are talking about synchronous rotation.

00:56:58 The temperature on the sunny side is so high that the metals melt and evaporate.

00:57:03 The other half of the planet is cold enough for the metals to condense again and fall back into the form of rain.

00:57:09 Speaking of synchronous rotation, the same thing happens with the Moon.

00:57:13 Our natural satellite has no dark side.

00:57:16 It's just that it always presents us with the same face.

00:57:19 When the Moon is between the Earth and the Sun,

00:57:22 what we call its dark side becomes very bright.

00:57:25 But it is impossible for us to observe it from our planet.

00:57:28 Yes, it's true that it is.

00:57:30 A recent study states that the Moon has a tail,

00:57:33 and every month it rolls around our planet like a scarf.

00:57:37 A thin strand of millions of sodium atoms follows our natural satellite,

00:57:42 and the Earth regularly crosses it.

00:57:44 Meteor showers dynamite these atoms of sodium out of the lunar surface

00:57:49 and project them far into space.

00:57:51 This may seem incredible, but the Moon seems to be shrinking.

00:57:55 Its diameter is now 46 meters less than a few hundred million years ago.

00:58:00 The reason for this phenomenon could be the cooling of the Moon's entrails.

00:58:05 This could also explain the earthquakes that occur on its surface.

00:58:09 Astronomers have recently discovered that Mars is active on a seismic level

00:58:14 and that earthquakes occur there regularly.

00:58:17 For several days every month, the Moon remains between the Sun and our planet.

00:58:22 It is at this moment that the gravity of the Earth captures the tail of sodium.

00:58:26 Dragged into its siege, it forms a long strip that wraps around the Earth's atmosphere.

00:58:31 This lunar tail is totally harmless.

00:58:35 It is also invisible to the human eye,

00:58:37 with a luminous intensity 50 times lower than what it can perceive.

00:58:41 During these rare days, only powerful telescopes can detect its pale yellowish glow in the sky.

00:58:47 The lunar strip resembles a shiny spot whose diameter is five times higher than that of the full Moon.

00:58:54 It turns out that many planets in the universe, even within our own galaxy,

00:58:58 contain liquid or frozen water.

00:59:01 The closest one is in our solar system.

00:59:04 It is Europe, one of Jupiter's satellites.

00:59:07 Scientists are almost certain that under its frozen surface is a real ocean of liquid water.

00:59:12 But it is still too early to worry about the possible existence of a form of life on these planets.

00:59:18 Liquid water is just one of the many elements that must be brought together

00:59:22 for life as we know it to appear.

00:59:25 The star of the galaxy GSN 069 is about to become a planet the size of Jupiter

00:59:31 over the next trillion years.

00:59:34 This could happen due to regular contact between the star and a black hole.

00:59:38 Astronomers first noticed unusual x-ray bursts,

00:59:42 strangely luminous, which occurred every 9 hours.

00:59:46 After studying the phenomenon,

00:59:48 scientists realized that it was a star orbiting a black hole.

00:59:53 The luminous star was nothing more than matter at its surface being sucked in by the black hole.

00:59:58 It turned out that in several million years,

01:00:01 the black hole had already transformed the red giant into a white dwarf,

01:00:04 and the process was not about to stop.

01:00:07 Astronomers found traces of phosphine in the atmosphere of Venus.

01:00:11 On our planet, this incolorable and flammable gas is often found where microbes live.

01:00:16 No wonder a new theory suggests that there could be life on Venus.

01:00:21 However, even if there was life on what is sometimes called the "star of the shepherd" in the West,

01:00:26 it could only have appeared in its atmosphere.

01:00:29 No living organism is a priori capable of surviving in the extreme environment of the planet.

01:00:35 The surface of Venus is extremely dry and does not contain liquid water.

01:00:40 The pressure there is 90 times higher than that exerted on Earth.

01:00:44 Temperatures often exceed 480 ° C,

01:00:48 which is quite hot to melt some metals.

01:00:51 Not very engaging as a holiday project.

01:00:54 However, millions of light years away from us,

01:00:57 there is a floating space cloud entirely composed of water.

01:01:00 It contains so much that it could fill all our oceans 140 trillion times,

01:01:05 which is just a little bit more than we need.

01:01:09 The origin of water on Earth is a mysterious enigma.

01:01:12 The most widespread theory explains that we owe its presence to ice comets and asteroids

01:01:17 that left behind gigantic craters,

01:01:20 but also the precious liquid substance that allowed us to develop.

01:01:24 But in space, there is a lot of organic matter,

01:01:28 and under specific conditions, it could produce enough water

01:01:32 to fill our oceans thousands of times in a row.

01:01:35 Researchers have conducted an experiment that consisted of heating this organic matter.

01:01:40 During this research, they have managed to obtain clear water and oil.

01:01:45 If this result is confirmed,

01:01:47 it could mean that the oil comes not only from fossilized remains of living beings,

01:01:52 but also that it could have come from space.

01:01:55 There could be about 6 billion planets similar to Earth,

01:01:59 just in the Milky Way.

01:02:01 Recent data have shown that a star similar to the Sun in 5

01:02:04 can have at least one planet in its habitable zone.

01:02:07 And be careful, not just any planet.

01:02:10 It would have a core, a rocky surface,

01:02:13 and would be comparable in size to that of Earth.

01:02:16 Located in the habitable zone of its star,

01:02:18 such a planet would have a high chance of becoming the cradle of living creatures,

01:02:22 if only microbes.

01:02:24 And if there are billions of these planets in our galaxy,

01:02:27 we can say without risk that at least one of them is potentially habitable,

01:02:31 or even already inhabited.

01:02:33 And now, let's multiply this number by the number of galaxies in the universe,

01:02:38 while keeping in mind that many of them are much larger than the Milky Way.

01:02:42 This gives us billions and billions of stars like the Sun,

01:02:46 and even more planets comparable to Earth,

01:02:49 some of which are surely very similar.

01:02:51 And now, hold on tight,

01:02:53 it could be that we are able to walk standing up thanks to the explosions of supernovas.

01:02:58 About 2.5 million years ago,

01:03:01 a supernova sent cosmic rays to our planet.

01:03:04 They triggered a series of electric storms in the Earth's atmosphere,

01:03:08 which turned into a storm.

01:03:10 These then caused forest fires in Northeastern Africa,

01:03:13 where the first humans lived.

01:03:15 The fires turned the forest area into a savannah,

01:03:18 atmospheric pressure changed,

01:03:20 and our ancestors had to stand on two legs to survive.

01:03:24 The largest explosion since the Big Bang was recorded in 2019.

01:03:29 It occurred in the Amma Ophiuchus, which brings together thousands of galaxies.

01:03:34 According to scientists, the explosion was equal to 20 billion billion,

01:03:39 that is, 18 zeros, of megaton explosions,

01:03:42 occurring once per millisecond for 240 million years.

01:03:47 In 2019, NASA's InSight lander,

01:03:51 whose goal was to study the interior of Mars,

01:03:53 recorded the very first earthquake of Mars.

01:03:56 These earthquakes occurred frequently, about twice a day,

01:04:00 and most of them were tiny.

01:04:02 You wouldn't even feel them if they were happening on our planet.

01:04:06 So far, more than 300 Martian earthquakes have been detected.

01:04:10 These are the first seismic shocks detected on another space body

01:04:14 than the Earth or the Moon.

01:04:16 The mission also revealed another mysterious phenomenon

01:04:20 by capturing strange magnetic pulses.

01:04:23 They occurred every day at midnight around the lander.

01:04:26 The source of these impulses has still not been clarified to this day.

01:04:31 Pluto's atmosphere rises much higher above the surface of the dwarf planet

01:04:35 than that of Earth.

01:04:37 It has about 20 layers, all glacial and extremely condensed.

01:04:42 You remember the asteroid that destroyed the dinosaurs on Earth.

01:04:45 Who could forget it?

01:04:47 There may have been another galactic shock

01:04:49 that ended badly for at least 75% of life on our planet.

01:04:54 About 360 million years ago,

01:04:56 a supernova explosion occurred around 65 light-years away from us.

01:05:01 And the cosmic rays it sent swept the ozone layer of our pretty blue ball.

01:05:06 This is what we call a difficult neighborhood.

01:05:09 Our Sun.

01:05:11 Scenario 1. Something strange has just happened.

01:05:15 All television and radio channels talk about a black hole

01:05:19 that has come close to us,

01:05:21 where our sun was.

01:05:24 You can even see a disc of accretion there,

01:05:27 and the background of the sky seems a little distorted,

01:05:30 which means it has really come close.

01:05:33 Normally, black holes are so far away that we can't see them with the naked eye.

01:05:37 We can't even see them with a telescope.

01:05:40 So what is it doing here, so close?

01:05:42 And where is our sun?

01:05:44 Did the black hole swallow it?

01:05:46 The sun was once at the center of our solar system,

01:05:49 far enough away not to burn us,

01:05:51 but close enough to give us light, heat,

01:05:54 and beautiful spectacles when it rises to the east and sets to the west.

01:05:58 And then it gave us life.

01:06:01 The most massive body of our solar system

01:06:04 contains 99.8% of its total mass.

01:06:07 It is so large that we could hold more than a million Earths inside.

01:06:11 Maybe our sun has turned into a black hole.

01:06:14 But it's too early for that to happen.

01:06:17 Yet, that's how it forms.

01:06:19 When huge stars reach the end of their life cycle and explode,

01:06:23 what we call a supernova,

01:06:25 they end up collapsing on themselves, becoming very small.

01:06:28 A tiny size and a colossal mass.

01:06:31 That's what makes the gravity of black holes so important.

01:06:34 And even the light that comes too close can't escape it.

01:06:37 Yet, all the stars in the universe shrink and disappear at some point.

01:06:42 Our sun loses 4 million tons of its mass every second.

01:06:46 And in the end, the only energy that will remain in the universe

01:06:49 will be generated by black holes.

01:06:51 A black hole is surrounded by dust, gas, and radiation.

01:06:55 Radiation is very dangerous,

01:06:57 so we hope our planet won't get too close to it.

01:07:00 Our solar system has no more light, no more heat,

01:07:04 so even Mercury and Venus will probably be covered in ice very soon,

01:07:09 not to mention the Earth.

01:07:11 Do we need to mention that nothing will survive this new ice age?

01:07:15 The only salvation could be the accretion disk,

01:07:18 which spins so fast that it generates heat,

01:07:21 but it's too risky to take.

01:07:23 At least, if the black hole has the exact same mass as our star,

01:07:27 all the planets will stay on the same orbits, including Earth.

01:07:31 But if it has a mass greater than that of our sun,

01:07:34 which is what our scientists are currently trying to determine...

01:07:37 So, goodbye, solar system.

01:07:39 Glad to have made you aware.

01:07:42 Oh no! What's going on?

01:07:44 It was supposed to be a beautiful sunny day,

01:07:47 but now you see the darkness fall suddenly.

01:07:50 How is it possible that it's night, when the clock indicates 2 p.m.?

01:07:53 And the Moon looks so different.

01:07:55 The news channels announce that our sun has disappeared,

01:08:00 and that because of some mysterious events,

01:08:02 the Moon is no longer in orbit around the Earth.

01:08:05 It is now in the center of our solar system.

01:08:08 We don't have much time left.

01:08:10 We have exactly 8 minutes and 20 seconds to realize it.

01:08:14 It may take millions of years for the energy of the sun to travel from its core to its surface,

01:08:19 but 8 minutes and 20 seconds is the time it takes for the sun's light to reach the Earth.

01:08:24 The light travels 150 million kilometers,

01:08:28 which corresponds to the distance that separates us from the sun.

01:08:31 We are no longer in the habitable zone.

01:08:33 It is the distance from a star, in our case, the sun,

01:08:37 to which liquid water could exist on the surface of a planet.

01:08:41 Now that the sun has disappeared, its light will no longer reach us,

01:08:44 and our planet will gradually become a frozen and lifeless rocky mass.

01:08:49 Who knows if we will have enough time to develop the technologies

01:08:52 that would provide us with the necessary solar energy to maintain life on Earth.

01:08:56 If this is not the case, well, millions or billions of years later,

01:09:00 scientists from other civilizations will explore our world,

01:09:03 trying to prove that life never existed there.

01:09:06 It is the same as what we do with Mars and other planets in our solar system.

01:09:11 This is how we try to determine whether they have always been sterile,

01:09:14 or if there may be a sign that some organisms once lived there.

01:09:18 Something else, also essential to life, travels at the speed of light, gravity.

01:09:23 Without the sun, for about 8 more minutes,

01:09:26 the planets will continue to rotate around the empty center of our solar system,

01:09:30 until the countdown stops and they end up drifting in an unknown direction in space.

01:09:35 Our moon does not have enough gravity to keep us in place.

01:09:39 It cannot shine enough to give us heat and allow life.

01:09:43 It is so far away that we can barely see it now.

01:09:46 Without the moon, which travels peacefully near our planet, as it did before,

01:09:50 we can see that the tides go down incredibly fast, and there is more and more wind.

01:09:55 The winds are so powerful and fast now.

01:09:58 When everything was normal, our planet was tilted by 23.5 degrees,

01:10:03 which explains the changes in weather and season.

01:10:06 Now, the tilt is so extreme that it is very cold, very fast.

01:10:11 And our time is almost over.

01:10:13 People are screaming, everyone is in panic.

01:10:16 We may have one minute left before we sink into eternal darkness.

01:10:20 Scenario 3

01:10:22 We do not know exactly what happened,

01:10:25 nor how the peaceful existence we were leading to ended.

01:10:28 No one could predict it, but it seems that, out of nowhere, a giant neutron star took the place of our sun.

01:10:35 It is not something we could have identified by ourselves.

01:10:38 We just noticed that something was different.

01:10:41 The sun has become smaller and a little weird.

01:10:43 The rest, we heard it from the information.

01:10:45 And no one knows how it happened.

01:10:47 Maybe our sun is somewhere behind the neutron star,

01:10:50 or that the star pushed it out of our solar system in an unknown direction.

01:10:55 A neutron star is the densest space object we know.

01:10:58 Its mass is almost twice as large as that of our sun,

01:11:02 but it is compressed in a star of only 15 km in diameter,

01:11:06 which corresponds to the size of a city on Earth.

01:11:08 A neutron star is formed when a huge star has no more fuel.

01:11:12 It collapses in a big explosion.

01:11:14 Its central region, the core, also collapses.

01:11:18 This is why each electron, a particle charged negatively,

01:11:21 and each proton, a particle charged positively,

01:11:24 collides to form a neutron, which has a neutral or zero charge.

01:11:29 We are in a very delicate situation now.

01:11:32 We have to wait for our end to come.

01:11:34 This neutron star has a gravity 2 billion times stronger than that of Earth.

01:11:39 This means that our new sun will pull all the planets of our solar system towards it,

01:11:45 and will eventually destroy them.

01:11:47 It has already begun.

01:11:48 For the first time in our knowledge, planets leave their stable orbits,

01:11:53 attracted by the colossal force of the neutron star.

01:11:56 It becomes very quickly chaotic.

01:11:59 And it will not stop there.

01:12:01 A neutron star rotates more than 700 times per second,

01:12:04 which is incredibly fast.

01:12:06 Our sun rotates on itself only once every 27 days.

01:12:10 So, after destroying all the planets, including ours,

01:12:13 this star will continue to spin in the universe at about 1/5 of the speed of light.

01:12:18 Maybe it will slow down and go out over time.

01:12:21 Or not.

01:12:23 After thousands of years, many neutron stars begin to slow down and go out.

01:12:28 But this does not always happen.

01:12:30 If it meets another star, it will begin to orbit around it

01:12:33 and will begin to feed on its atmosphere,

01:12:36 until it collapses after a while and turns into a giant black hole.

01:12:40 Our sun was going to go out anyway.

01:12:43 Until the neutron star appeared, the sun was 4.6 billion years old,

01:12:49 about half its lifespan.

01:12:52 It had already burned about half of its hydrogen reserves

01:12:55 and had enough reserves for 5 billion additional years.

01:12:59 It was supposed to eventually reach the size of the Earth.

01:13:01 After exhausting its fuel, it would simply have collapsed.

01:13:05 It would have retained its enormous mass,

01:13:07 but its volume would have been similar to that of our planet.

01:13:11 No sun, no life.

01:13:13 So the result would have been pretty much the same.

01:13:15 But in this way, the process would have been slow.

01:13:18 And who knows if humans would still have inhabited the same solar system at that time.

01:13:22 But with neutron stars, things go much faster.

01:13:26 And it's much more unpredictable.

01:13:28 If a neutron star went crazy, somewhere far away in another galaxy,

01:13:32 we would only see it in the form of a far-off flashing light

01:13:36 that we call a pulsar.

01:13:38 And then suddenly... boom!

01:13:40 That's it! The James Webb telescope has been fully deployed.

01:13:46 If you are interested in astronomy or space,

01:13:49 you can be delighted with this progress.

01:13:51 And here's why.

01:13:52 To begin with, it's huge.

01:13:54 The JWST's primary mirror is more than 6 meters wide.

01:13:59 The Hubble Space Telescope, the previous largest eye in space,

01:14:02 has a mirror of about 2.27 meters.

01:14:06 For comparison, if you placed the two telescopes side by side,

01:14:09 it would be like putting a horse next to an elephant.

01:14:12 A big adult elephant.

01:14:14 There is a perfect reason why the Webb, as it is affectionately called, is massive.

01:14:18 It is not an optical telescope in the traditional sense of the term,

01:14:21 like most of its likelihoods.

01:14:23 The JWST is an infrared telescope.

01:14:26 It perceives heat.

01:14:28 Infrared light has a wavelength longer than visible light.

01:14:32 So it needs a bigger mirror to focus that light.

01:14:35 With the James Webb Space Telescope,

01:14:37 we have two things we've never seen before.

01:14:40 On the one hand, a new technology,

01:14:42 and on the other hand, incredible scientific missions.

01:14:46 Mission and technology are both at the forefront of progress.

01:14:50 The Webb is a classic example of engineering in the service of science.

01:14:54 Thanks to its great ability to collect light,

01:14:58 the James Webb Space Telescope will be able to capture images of things

01:15:01 we have never seen before, but that we have always wanted to see.

01:15:05 Things like exoplanets, the first galaxies in the universe,

01:15:09 and stars and planets forming inside nebulae.

01:15:13 Not to mention that there will also be, no doubt, a lot of surprises.

01:15:17 The James Webb Space Telescope has several technological things in its sleeve

01:15:21 that promise to lead to the greatest scientific discoveries.

01:15:25 The Webb has a coronagraph, which is very special.

01:15:29 The coronagraph is the tool that will allow us to take the first real photos of exoplanets.

01:15:34 The coronagraph blocks the bright, punctual light of the stars,

01:15:38 of which we already know that they have planets orbiting around them.

01:15:41 Without the coronagraph, the light of these stars would make things too bright

01:15:45 to see the exoplanets, which are hundreds of thousands of times more tern than their stars.

01:15:50 But with the coronagraph, which blocks the light of the stars,

01:15:53 the exoplanets are visible.

01:15:55 And the coronagraph of the James Webb Space Telescope can block the light of a hundred stars at the same time.

01:16:01 We can expect a spectacle of exoplanets.

01:16:04 This brings us to the next high-tech gadget that the James Webb Space Telescope is equipped with,

01:16:08 a spectrograph without a slit.

01:16:11 Usually, an ordinary spectrograph has a slit to allow a flash of light to enter and be diffracted.

01:16:17 Diffraction is the dispersion of light to reveal the spectrum of the wavelengths that make it up.

01:16:22 But the work of the James Webb Space Telescope is so sensitive that a flash of light would submerge the lens.

01:16:28 A spectrograph without a slit has therefore been installed.

01:16:31 The light of the stars collected by the large mirror is sent into a fiber optic cable

01:16:36 to send only one point of light into the spectroscope.

01:16:39 And that's where the grisble takes over.

01:16:42 Sir Isaac Newton used a prism to discover the spectrum of sunlight, as you may remember.

01:16:49 But the Webb uses a grisble.

01:16:51 It's an English word made up of two other words, "grated prism", which means "prisma grille".

01:16:57 This means that it has very small slits that diffract the point of light

01:17:01 that the large mirror sends along the fiber optic cable and into the spectrograph.

01:17:05 The science that consists of reading a spectrum of light is called spectroscopy.

01:17:09 By analyzing the light spectrum from exoplanets,

01:17:12 the JWST will determine which gases are in the atmosphere of them,

01:17:17 as well as their density and even their temperature.

01:17:20 It's an incredible advance in our knowledge.

01:17:23 We will be able to say whether a planet contains oxygen or nitrogen or methane,

01:17:28 or even other gases that could or could not indicate that the planet is habitable.

01:17:32 Another Earth, maybe.

01:17:34 Currently, the JWST is stationed in its permanent location.

01:17:39 Unlike the Hubble Space Telescope, which orbits the Earth,

01:17:42 the James Webb Space Telescope orbits around the Sun.

01:17:46 It orbits around the Sun at one of the gravitational equilibrium points between the Earth-Sun system.

01:17:51 It simply stays there, not using much or very little fuel to maintain its position.

01:17:57 As the Earth is orbiting around the Sun,

01:17:59 the James Webb Space Telescope is stationed in a place that is also orbiting around the Sun.

01:18:04 There are five gravitational equilibrium points between the Earth and the Sun.

01:18:08 They are called the Lagrange points,

01:18:10 named after their discoverer Joseph Louis Lagrange in the 18th century.

01:18:15 The Webb is stationed on point L2,

01:18:17 the second of the five Lagrange points,

01:18:19 which is 1.5 million km away in space,

01:18:22 well beyond the Moon.

01:18:24 All this to observe an infrared light point.

01:18:27 But first, engineers must find or acquire this light point.

01:18:32 To obtain an infrared light point,

01:18:34 the 18 hexagonal mirrors must be unfolded from their position inside the Ariane rocket,

01:18:40 which sent Webb into space.

01:18:42 Once the mirrors are unfolded,

01:18:44 their positions must be adjusted with microscopic precision

01:18:47 so that the 18 mirrors produce a single image.

01:18:51 Several tiny motors are attached to each segment of the mirror to make these adjustments.

01:18:56 These motors, which must be activated individually,

01:18:59 will gradually pull the segments of the mirror into the shape of a bee's nest to align them.

01:19:04 This is an essential part of the mission,

01:19:06 and it takes months to do it right.

01:19:09 To align the mirrors, in order to produce a single light point,

01:19:12 the James Webb Space Telescope must not be shaken.

01:19:15 It must be kept absolutely still.

01:19:18 And this requires two other cutting-edge technologies,

01:19:21 the solar steam and cryogenic cooler.

01:19:25 In space, the direct sunlight is very hot,

01:19:28 and the shadow is very cold.

01:19:31 This is why the James Webb Space Telescope

01:19:33 has brought its own high-tech solar steam,

01:19:36 which is huge, as it is as large as a tennis court.

01:19:39 Composed of five individual layers of 1 mm thick Kapton film,

01:19:44 each layer of the solar steam must be deployed individually at a distance

01:19:48 using an 8-motor system and 139 actionaries,

01:19:52 including thousands of pieces.

01:19:54 The purpose of the solar steam is to help the JWST stay cold.

01:19:58 The colder it is, the better.

01:20:00 As for the cryogenic cooler, it is used to make it even colder.

01:20:04 The temperature can be measured in three different ways.

01:20:07 In Fahrenheit, where water freezes at 32°C and boils at 212°C.

01:20:12 In Celsius, where water freezes at 0°C and boils at 100°C.

01:20:16 But none of these thermometers have a starting point.

01:20:19 In the 19th century, Lord Kelvin therefore imagined a third temperature scale,

01:20:24 the Kelvin scale, which starts at absolute zero,

01:20:27 the coldest possible temperature.

01:20:29 The onboard cryogenic cooler will cool the JWST

01:20:33 to only 7°K, or 7° above absolute zero.

01:20:38 At this temperature, almost all the heat from the engines will be eliminated,

01:20:43 and the telescope will be able to focus on the light of a single point

01:20:46 without any noise, in other words, movement, interfering with the image quality.

01:20:52 Finally, after all this incredible technology has been put into operation remotely,

01:20:57 and as planned, we are almost ready to observe the infrared images

01:21:01 of the multi-segmented giant mirror that the James Webb Space Telescope has.

01:21:06 Almost ready.

01:21:07 A telescope can collect all the light it wants,

01:21:10 but in the end it must also be able to detect what it has collected.

01:21:15 If the light is not detected, it is not really observed.

01:21:18 This is where infrared detectors come in.

01:21:21 Webb has 15 of them.

01:21:23 This specially made semiconductor material produces a slight electric charge

01:21:27 when hit by an infrared light photon.

01:21:30 Webb's infrared detectors can produce a high-definition image of 1 million pixels.

01:21:36 Some of the detectors can even produce an image of 4 million pixels.

01:21:40 They must be durable enough to last 10 to 20 years, without deforming or corrupting,

01:21:46 while working at 7 degrees above absolute zero.

01:21:50 For them alone, the JWST's infrared detectors are a marvel of engineering.

01:21:55 But what will they take photos of?

01:21:57 We come to the JWST's mission.

01:22:00 They are also on the verge of progress.

01:22:02 70 of the 280 first target observations are exoplanets.

01:22:07 Is there another Earth?

01:22:09 Which exoplanets seem habitable?

01:22:11 Webb's telescope will provide a detailed spectroscopic analysis

01:22:15 of the atmosphere of thousands of known exoplanets.

01:22:18 For the first time, we will see images of exoplanets

01:22:21 as they appear in infrared light.

01:22:24 Cosmology, the study of the universe, may be Webb's main mission.

01:22:28 The galaxies that move away so quickly that their light is drawn into the infrared

01:22:32 will be a target for the study.

01:22:35 Hundreds of hours of observation are necessary to collect the low infrared light

01:22:39 of the first galaxies formed after the Big Bang.

01:22:42 The JWST will give us an image of what the universe looked like when it was born.

01:22:48 Astronomers will learn new information about dark energy,

01:22:52 which is the origin of the universe's expansion,

01:22:54 and the role that dark holes may play in the formation of galaxies.

01:22:59 The formation of stars in the Milky Way and nearby galaxies

01:23:02 is also part of Webb's mission.

01:23:04 By giving an image of hundreds of solar systems forming around rising stars,

01:23:09 astronomers will establish a precise history of the development of solar systems.

01:23:14 From now on, facts will replace theory,

01:23:17 and a big step forward will be made in our understanding of space.

01:23:21 The James Webb Space Telescope is a bold project

01:23:25 that will make an important step in the history of science.

01:23:30 It is said that somewhere, there is a pen that can work in gravity,

01:23:34 at extreme temperatures and even underwater.

01:23:37 That this pen can write on almost all surfaces, even upside down,

01:23:42 and this at temperatures that can reach 300 degrees.

01:23:46 It is also said that NASA has spent millions, if not billions of dollars

01:23:50 and almost a decade, to develop such an object.

01:23:53 The problem with ballpoint pens in space

01:23:56 is that they do not work in gravity.

01:23:59 The ink cannot flow to the ball normally,

01:24:02 since gravity does not affect it.

01:24:04 Instead, pressure is applied to the ink tank,

01:24:07 and the pens start to run away.

01:24:09 Until recently, NASA used paper pencils.

01:24:13 Being made of wood, they represented a risk of fire

01:24:16 in most of the space ships of the time,

01:24:19 whose internal atmosphere was composed of 100 degrees of oxygen.

01:24:22 The need for a super pen was therefore obvious.

01:24:26 But whatever the rumors say, NASA did not create such a pen,

01:24:30 nor did it spend a fortune on research.

01:24:32 Its development was sponsored by Paul C. Fischer,

01:24:35 of the Fischer-Penn Company, based in Chicago.

01:24:38 More than a million dollars and nearly 10 years were needed

01:24:41 to develop a pressurized ink cartridge.

01:24:44 It was to allow space pens to operate in zero gravity

01:24:48 and in other extreme conditions.

01:24:50 In short, they got a pen that could be used at low temperatures,

01:24:54 ranging from -35°C to 120°C.

01:24:56 Impressive, isn't it?

01:24:58 The pen was patented in 1966.

01:25:00 A year later, after conducting several tests,

01:25:04 NASA started to equip astronauts with Apollo missions.

01:25:08 Surprisingly, the rumors that NASA spent a fortune

01:25:12 on developing space pens have been circulating for decades.

01:25:16 They have been denied many times,

01:25:18 but they are resurfacing again and again.

01:25:21 Many science fiction movies can make you think

01:25:24 that everything that happens in space is accompanied by a kind of sound effect,

01:25:28 which is a totally false idea.

01:25:30 In space, no one hears you scream.

01:25:32 Do you know why?

01:25:33 Because there is no air in space.

01:25:35 It is an almost perfect vacuum

01:25:37 that makes the movement of sound waves impossible.

01:25:40 They cannot reach your pens

01:25:42 and make them vibrate to send the signals necessary to your brain.

01:25:46 But it's a good thing,

01:25:47 especially for astronauts when they go out into space.

01:25:50 Without the calm of the space vacuum,

01:25:52 they would be constantly submerged by the noise of solar storms.

01:25:56 Here is another well-received idea.

01:25:58 All comets have beautiful and long tails.

01:26:00 It's just a popular myth.

01:26:02 In reality, comets are very difficult to spot in space.

01:26:05 They usually spend a lot of time far from the stars.

01:26:08 There, in the darkness of space,

01:26:10 they remain rather inactive and completely frozen.

01:26:13 Comets have a tail only when they approach a star.

01:26:16 It is at this moment that they begin to warm up.

01:26:19 This process leads them to develop a kind of cloud atmosphere

01:26:22 called a coma and a distinctive tail.

01:26:25 The tail always points to the opposite side of the star that influences the comet

01:26:29 because it is pushed in the opposite direction by the radiation and solar winds.

01:26:33 That's why the tail can also be in front of the comet and not behind it.

01:26:38 Now let's see what a light year is.

01:26:41 The very name of this notion can suggest that we are talking about time.

01:26:45 In reality, light years are a unit of distance.

01:26:49 The definition of a light year by NASA is as follows.

01:26:52 The total distance that a beam of light travels in a straight line

01:26:56 takes one year.

01:26:58 And since light travels at a speed of 300,000 km per second,

01:27:01 a light year is almost 9 billion km.

01:27:05 People often believe that we are experiencing zero gravity in space.

01:27:09 Hence the weight that astronauts feel in the International Space Station.

01:27:13 But that's not quite true.

01:27:15 Gravity is one of the most important forces in the universe.

01:27:19 Thanks to it, the Moon can rotate around the Earth

01:27:22 and the Sun does not drift far from our galaxy, the Milky Way.

01:27:26 ISS astronauts do not experience zero gravity, but microgravity.

01:27:31 Gravity on the space station is only 10% lower than gravity on Earth.

01:27:37 But astronauts are constantly free-falling.

01:27:40 In a space vehicle, people who are on board fall forward all the time,

01:27:45 not downwards, but around our planet, following a specific orbit.

01:27:49 And since they all fall together, the crew and the objects inside seem to float.

01:27:54 This is why astronauts can move objects weighing hundreds of kilos at the tip of their fingers.

01:27:59 And even though microgravity is often called zero gravity,

01:28:02 these are actually two very different things.

01:28:05 You can get the impression that the Sun is always on fire.

01:28:08 At least, that's what the photos show.

01:28:10 But in reality, our star is a giant gas ball.

01:28:14 Nuclear reactions that occur permanently in its core burn the Sun.

01:28:19 Every second, hundreds of millions of tons of hydrogen are transformed into almost as much helium.

01:28:25 During this process, huge amounts of energy are released in the form of gamma rays.

01:28:30 Then these rays turn into light.

01:28:32 In other words, the Sun actually emits a blinding light and an incredible heat.

01:28:37 But it's not really on fire, because there's no oxygen involved in the process.

01:28:42 A human can explode if he goes into space without a space suit.

01:28:46 Well, contrary to popular belief,

01:28:48 taking off a space suit during a spacewalk won't be as dramatic as what we often see in movies.

01:28:55 The person will simply lose consciousness due to a lack of oxygen

01:28:59 after 15 seconds in space without protection.

01:29:02 Before that happens, he will have to exhale as much air as possible,

01:29:06 otherwise this oxygen will damage his lungs inside.

01:29:09 Then, without the protection of the space suit, which acts like a mini space ship,

01:29:14 the pressure inside his body will drop.

01:29:17 This will cause even more serious problems.

01:29:20 And even if this person certainly won't explode,

01:29:22 she won't have any interest in staying outside for too long.

01:29:25 We often hear that black holes are gigantic and terrifying cosmic vacuum cleaners.

01:29:30 But in reality, black holes are more like a fly trap.

01:29:34 They are not constantly looking for things to suck.

01:29:37 Instead, they stay there, quite passively.

01:29:40 It's only when a star gets too close that a black hole comes into action.

01:29:44 And again, only space objects that cross a certain border are torn apart.

01:29:49 If the Sun were suddenly replaced by a black hole, the Earth's orbit wouldn't change.

01:29:54 However, its temperature would be different.

01:29:57 Our planet would no longer be affected by magnetic storms or solar winds.

01:30:02 Let's suppose that this black hole is the same mass as our star.

01:30:05 According to the laws of physics, the Earth would have to get really close to be dragged into it.

01:30:11 The legend of the dark side of the Moon was demystified more than 50 years ago.

01:30:16 Yet, not everyone knows that this dark side is simply the part of the Earth's natural satellite,

01:30:22 which is oriented on the opposite side.

01:30:24 It is by no means darker than the rest of the Moon.

01:30:27 And the Sun's light reaches the entire lunar surface equally.

01:30:32 If it seems darker, it's only because we can never see it from the Earth.

01:30:36 This is the result of a phenomenon known as "synchronous rotation".

01:30:41 Over billions of years of space history,

01:30:44 the gravitational link between our planet and its natural satellite has changed their orbits.

01:30:49 Their speed of travel has also changed.

01:30:52 And since the Earth is much more voluminous than the Moon,

01:30:55 the rotation of the satellite has been gradually slowed down,

01:30:59 until it reached its equilibrium point.

01:31:02 And today, it takes the same time as the Moon to make a complete rotation on its axis

01:31:07 and to make a complete orbit around the Earth.

01:31:10 You may have heard people talk about Venus as the twin of the Earth.

01:31:14 It is true that these two planets are almost the same size.

01:31:17 They also have a similar mass and composition.

01:31:20 The gravity on the surface of Venus is equivalent to 91% of that of the Earth.

01:31:25 So if you weigh 45 kilos on our planet, you would weigh 40 on Venus.

01:31:30 And yet, to qualify these twin planets is very exaggerated.

01:31:34 Venus's atmosphere is 100 times thicker than that of the Earth.

01:31:37 In addition, the temperatures on its surface are incredibly high, up to 455 degrees.

01:31:43 It's hot enough to melt lead or carbonize your pizza.

01:31:47 Venus doesn't have an ocean filled with liquid water or any form of life.

01:31:51 It also rotates in reverse compared to all the other planets in the Solar System, including the Earth.

01:31:57 By the way, another myth claims that Mercury is the hottest planet in the Solar System.

01:32:02 After all, it's the planet closest to the Sun.

01:32:04 But in reality, Venus is hotter.

01:32:07 Asteroids hit the Earth much more often than people tend to believe.

01:32:11 But the vast majority of these collisions are far from being the kind of cataclysmic event

01:32:16 capable of turning history upside down, causing, for example, a massive extinction.

01:32:21 Most of them go by completely unnoticed.

01:32:24 Most of the asteroids that approach our planet are classified as geocruisers.

01:32:28 They are generally consumed in the Earth's atmosphere

01:32:31 before they have the slightest chance of destroying life on the planet's surface.

01:32:35 They're not big enough to do that.

01:32:38 And yet, about 40 to 80 tons of space debris fall on Earth every year.

01:32:43 Most of these debris are tiny asteroids, also called "bolides."

01:32:48 They're generally no more than 20 meters in diameter.

01:32:52 Space suits are made up of different materials, elements, and mechanisms

01:32:57 to protect the body from the vacuum of space.

01:33:00 And that's a good thing.

01:33:02 No living being can float without protection against ice temperatures and oxygen absence.

01:33:08 Not to mention the burning rays of the sun and various objects that could potentially crash on you.

01:33:14 The technical term for a space suit is "extravehicular mobility unit."

01:33:20 They're extremely durable, and their manufacturing is priceless.

01:33:24 Each suit can cost up to $10.4 million.

01:33:28 All space suits are custom-made,

01:33:31 with their various accessories and components being designed and manufactured by 80 different companies.

01:33:37 The size of the components can vary, and can fit in the palm of your hand,

01:33:41 or can be up to 75 centimeters.

01:33:44 A suit has 18 distinct elements, and is made up of 16 layers.

01:33:48 In reality, there are 14, but if you add the two inner layers, that makes 16 in total.

01:33:54 That's all.

01:33:56 Over the decades, the space suit has evolved into what it is today,

01:34:00 a mini human-shaped space ship.

01:34:03 It's designed to reproduce the living conditions in the Earth's atmosphere,

01:34:07 so that astronauts can survive in space.

01:34:10 It has a system that allows oxygen to be supplied and carbon dioxide to be expelled.

01:34:15 It's strong enough to protect astronauts from solar radiation, sun rays, and micrometeorites.

01:34:22 The conditions outside our atmosphere can be extremely rigorous.

01:34:26 That's why the suits are equipped with a temperature control system and a pressure-sensitive sump.

01:34:31 The temperatures outside the suit can go from 120 degrees Celsius...

01:34:35 Ouch!

01:34:36 ...to -150.

01:34:38 They are designed to preserve life outside our atmosphere.

01:34:42 The main part of the suit is a cooling garment made of nylon, fiberglass, and tubes.

01:34:49 It is specially designed to contain about 90 meters of tubes,

01:34:53 woven very densely inside a garment that covers the entire body,

01:34:57 except the head, feet, and hands.

01:35:00 Cold water flows into the tubes near the skin to regulate the body's temperature

01:35:05 and cool it down during its stay in space.

01:35:08 It's a bit like your computer's fan, which cools your machine when it overheats.

01:35:14 The garment is connected to a survival system.

01:35:17 The survival system is one of the most important parts of the suit,

01:35:21 and its assembly requires meticulous work.

01:35:24 Everything in this compartment is essential to the astronaut's survival.

01:35:29 Any miscalculation could be catastrophic and even endanger their lives.

01:35:34 Oh dear!

01:35:35 This is where the oxygen tanks are located,

01:35:38 filled and closed hermetically.

01:35:41 Thanks to an oxygen tank, they can last up to 7 hours.

01:35:44 A secondary tank adds about 30 minutes of oxygen to the one or more in the suit.

01:35:51 Astronauts cannot afford to waste oxygen when they leave their station.

01:35:55 They therefore learn to breathe properly.

01:35:58 The carbon dioxide is also expelled,

01:36:02 including a filtration cartridge made of lithium hydroxide,

01:36:05 which is also attached to a tube.

01:36:07 This way, there is no toxic carbon dioxide in the suit,

01:36:13 which permanently purifies the one it contains.

01:36:16 Next to that, there is a fan that cools the astronaut when he moves.

01:36:21 Wearing such a heavy suit is not easy and requires a lot of physical effort.

01:36:26 Even if the gravity is lower up there,

01:36:29 you still have to move your arms and legs, which can be tiring in the long run.

01:36:33 There is also an electric power source and a bidirectional radio to communicate with the base.

01:36:39 And just in case something happens,

01:36:41 an alert system is installed to warn the astronaut of the system's failures.

01:36:46 Oh oh!

01:36:47 Finally, there is the hydraulic cooling system that keeps the body at a good temperature.

01:36:52 Once the survival system is assembled, it is attached to the upper part of the torso, which is rigid.

01:36:58 The suit's helmet, designed for spacewalks,

01:37:01 is made of pressure chambers and is made of plastic.

01:37:05 There is a ring at the neck level to hold it in place,

01:37:08 with a sas and a ventilation system that provides oxygen to the astronaut.

01:37:13 And it is also connected to an emergency oxygen bottle, just in case.

01:37:17 While astronauts work in space, they might want to drink some water.

01:37:22 And luckily, there is an integrated straw so they can do it.

01:37:26 And also, we must not forget, the sun shines constantly and can be dazzling.

01:37:31 To protect the astronaut from these rays, a visor is installed, with the coating in gold.

01:37:37 And what is a space suit helmet without a camera to record everything?

01:37:42 As the bidirectional radio is connected to the survival system,

01:37:45 the headphones and the microphone are placed in the chin rest,

01:37:48 and the astronaut can communicate with the base.

01:37:51 Space can be dark. Yes, in reality, it is most of the time.

01:37:55 So there is an integrated lamp that they use during operations on nearby objects.

01:38:00 But let's continue our spacewalk.

01:38:03 Fixed to the lower unit of the torso, we have the pants and boots.

01:38:07 There is also a connection that goes from the knee to the ankle and the waist,

01:38:11 and which includes a pressurized pocket made of a specially taut nylon.

01:38:15 Most of these elements are made from durable materials adapted to space missions,

01:38:20 and also make up an elegant evening outfit for the astronaut who likes to go out at night.

01:38:25 You can adjust the size of the rings at the level of the thighs and legs when you want.

01:38:30 It's a good thing when the astronaut goes out to walk and to stretch his legs.

01:38:34 The astronaut also wears thermal socks under his hiking boots,

01:38:38 which are equipped with a heating system that keeps his toes warm.

01:38:42 The upper part of the torso is both rigid and light.

01:38:45 It is made of metal and glass fiber and connects the inside of the suit to the survival system.

01:38:51 It looks like a T-shirt and the sleeves of the suit are attached to it, which go up to the wrist.

01:38:56 It also attaches to the helmet ring.

01:38:59 There are water and oxygen tanks and many other equipment necessary for space.

01:39:04 The most recent space suits are designed with a back entrance so that the astronauts can slide inside.

01:39:11 What a style!

01:39:13 A control module located in the area of the torso allows the astronaut to check the outside conditions

01:39:18 and to monitor fluids and electricity.

01:39:21 The gloves are sturdy enough to protect the astronauts when they touch and pick up objects

01:39:26 while they work outside the space station.

01:39:29 They are designed so that all fingers can move easily.

01:39:33 It is the part of the body that cools down the fastest in space.

01:39:36 That is why the gloves also have a heating system.

01:39:40 The design of a space suit, with all its details, requires a large number of steps.

01:39:46 It is not exactly like when you knit a sweater.

01:39:49 It starts with the integration of the design, then the modeling.

01:39:53 Thus, the designers can know what the final product will look like without having to assemble all the elements.

01:40:00 And once the model is approved, they start to put together all the necessary materials, which can take some time.

01:40:07 Once this step is completed, they start manufacturing and assembling, which can also take a lot of time.

01:40:13 In total, seven parts will be created and sent to NASA for final assembly.

01:40:18 When an astronaut leaves the International Space Station,

01:40:21 he must be attached to it with a safety strap.

01:40:25 This way, he does not risk drifting while he is doing his maintenance work.

01:40:30 The longest spacewalk lasted a total of 8 hours and 56 minutes,

01:40:35 and the suits went a long way.

01:40:38 During the Apollo 11 mission,

01:40:40 Neil Armstrong was not able to move around the Moon in a very efficient way,

01:40:44 even though technically he was the first to do so.

01:40:48 In fact, he made leaps and bounds.

01:40:50 But with the latest technological innovations, astronauts can now walk and move around space very easily.

01:40:57 NASA plans to return to the Moon by 2024

01:41:01 and is preparing two new space suits,

01:41:03 with cutting-edge technology and optimal comfort for movement and work.

01:41:08 This suit is called XEMU,

01:41:11 and its design is very similar to that of astronauts in the International Space Station.

01:41:16 The new models and their characteristics will allow humans to live and work on the Moon.

01:41:22 We know from a recent demonstration that they are much more flexible than the previous models.

01:41:28 You can lean and turn in all directions at the waist level.

01:41:32 The leg section allows astronauts to walk with ease.

01:41:35 Among the secondary modifications,

01:41:37 the lightning fastening and cables have been removed

01:41:40 to prevent dust from infiltrating the suit.

01:41:44 You may think that the Earth is massive,

01:41:47 but the Sun represents nearly 99.9% of the mass of the entire solar system.

01:41:53 The rest of this mass is made up of planets and their satellites, asteroids, comets, gas and dust.

01:42:00 The Sun is located about 150 million km from our planet,

01:42:04 but it keeps us warm every day.

01:42:06 Its temperature is about 5,500 ° C,

01:42:09 but the space around it is always as cold as ice.

01:42:13 To understand this, we must distinguish between heat and temperature.

01:42:17 Heat is the energy that is inside an object.

01:42:20 Temperature is what tells us whether the object is hot or cold.

01:42:25 When heat is transferred from this object, the temperature increases.

01:42:29 When the object loses heat, its temperature decreases.

01:42:33 Heat can be transferred in three different ways.

01:42:36 The Sun does it by radiation.

01:42:38 This means that it releases heat in the form of light.

01:42:41 Your body also releases heat in the form of infrared waves.

01:42:45 This is why thermal cameras can detect your presence in a room, even at night.

01:42:50 The hotter the object, the more heat it releases.

01:42:53 Temperature affects only matter.

01:42:55 Since space is mainly empty, it does not contain enough particles

01:42:59 for heat to be transferred in other ways than by radiation.

01:43:03 When heat from the Sun arrives on an object,

01:43:06 the atoms begin to absorb energy.

01:43:08 But heat cannot be transferred because there is no matter in space.

01:43:12 These rare atoms and molecules in space will absorb heat,

01:43:16 and they will simply remain that way, while the cold vacuum will remain cold.

01:43:21 There is a lot of matter in the Earth's atmosphere,

01:43:24 so the Sun's energy can be transferred easily.

01:43:27 But if you put an object out of the Earth's atmosphere in the sun,

01:43:31 it will end up being heated to 121 ° C,

01:43:35 because it is a matter made up of atoms and molecules.

01:43:39 The temperature in the vacuum is -270 ° C.

01:43:43 This means that depending on where you are,

01:43:46 space can either burn you or freeze you.

01:43:49 The Sun is not really yellow.

01:43:51 It emits light over a wide range of wavelengths.

01:43:55 We can determine its temperature and color by the peak of its spectrum.

01:43:59 For example, the colder stars will be red,

01:44:02 and the warmer stars will be blue.

01:44:05 Between the two, yellow, orange and white stars.

01:44:08 As for the Sun, the spectrum culminates at a wavelength

01:44:12 that we generally define as green.

01:44:14 But our eye sees it differently.

01:44:16 Thus, this nuance of green, combined with other spectrum wavelengths,

01:44:20 will appear white to the human eye.

01:44:23 We generally perceive the Sun as yellow,

01:44:26 because our atmosphere diffuses blue light more effectively than red.

01:44:30 During sunrise and sunset,

01:44:32 there is more red light in the Sun's spectrum,

01:44:35 which gives us sparkling colors.

01:44:37 Solar stains are visible parts of the Sun's surface

01:44:40 that are, on average, much colder than the Sun itself.

01:44:44 They overlap with parts with an increased magnetic field.

01:44:47 These parts do not allow the release of heat

01:44:50 to the visible surface of the Sun.

01:44:52 Thus, the rest of the Sun's surface is three times brighter than these solar stains.

01:44:57 This contrast makes them appear almost black.

01:45:00 If we could separate a solar stain from the Sun

01:45:03 and place it somewhere in the night sky,

01:45:05 it would be different, as bright as the Moon

01:45:08 when we see it from Earth.

01:45:10 All the planets in our solar system rotate in the same direction,

01:45:14 because they are formed from a single protoplanetary cloud,

01:45:17 with the exception of Uranus and Venus.

01:45:20 They probably underwent a strong impact

01:45:22 that made them rotate in the opposite direction.

01:45:25 But this is different with galaxies.

01:45:27 They are generally not formed from the same cloud of dust and particles.

01:45:31 In addition, they are not randomly distributed in space.

01:45:35 They are formed in the form of filaments,

01:45:37 dense and thin strands of black matter and galaxies,

01:45:40 with gaps between them.

01:45:42 Protogalaxies are connected by gravitational forces

01:45:45 in small areas of space.

01:45:47 This is probably due to the distribution of black matter in the universe.

01:45:52 The matter in the filaments moves in a "cork"

01:45:56 and goes to the densest area.

01:45:58 So there could be a common direction

01:46:00 in which galaxies tend to rotate,

01:46:03 but it is mainly random.

01:46:05 It is possible that one day we would develop a lunar elevator.

01:46:09 Yes, a cable anchored to the surface of the Moon.

01:46:12 It would extend over 400,000 km.

01:46:15 We could not attach it directly to our planet,

01:46:18 because the Earth and the Moon are both moving.

01:46:21 But we could keep it,

01:46:23 high in the orbit of our planet.

01:46:25 Some researchers think that we could build such an elevator

01:46:28 for a few billion dollars.

01:46:30 The Moon has resources that we could certainly use.

01:46:34 A rare form of helium found there

01:46:36 could be useful in the fusion plants of our planet.

01:46:40 We could also take other rare elements

01:46:42 and use them in smartphones and the rest of electronics.

01:46:46 Thus, after about 53 ups and downs,

01:46:49 the elevator could be cushioned.

01:46:52 The cable would be as thick as a pencil,

01:46:54 but its weight would be about 40 tons.

01:46:57 It could even be made from the material we already have on Earth,

01:47:00 without having to invent anything.

01:47:03 It could even be a combination of two elevators.

01:47:07 A space ship would tow an elevator from the surface of our planet

01:47:10 to a space station.

01:47:12 Then it would be projected towards the Moon.

01:47:15 There would be another elevator to finally bring it down

01:47:17 to the surface of the Moon.

01:47:20 The planets of our solar system have predictable and stable orbits,

01:47:24 but collisions of gas giants could occur at an early stage

01:47:28 when the planetary system was still in formation.

01:47:31 In the event of a frontal collision,

01:47:33 two gas giants would fuse.

01:47:35 They would not end up losing their mass,

01:47:38 the materials of their gas envelopes,

01:47:40 or those of their solid nuclei.

01:47:42 Such a collision at a higher speed

01:47:44 would cause the loss of most of the gas in the envelope.

01:47:47 And at a very high speed,

01:47:49 boom, the two planets would disappear.

01:47:52 It would be different if the collision was not frontal.

01:47:55 If the two nuclei could be completely avoided,

01:47:58 the gas giants would not fuse,

01:48:00 but they would lose part of their mass.

01:48:02 The gas giants could even change shape

01:48:05 because of such a collision.

01:48:07 Astronomers have discovered that there is an extremely distant galaxy from us

01:48:11 that looks like our Milky Way.

01:48:14 We see it today as it was when the Universe was only 1.4 billion years old.

01:48:19 Today, it is 13.8 billion years old.

01:48:23 It took more than 12 billion years

01:48:25 for the light from this distant galaxy to reach our planet.

01:48:30 This galaxy is peaceful, stable, and surprisingly not chaotic,

01:48:34 unlike all the other galaxies that were quite turbulent at the beginning.

01:48:39 To leave the Milky Way,

01:48:41 we would have to travel at about 25,000 light-years from the centre of the galaxy

01:48:45 or 500 light-years vertically.

01:48:49 Our galaxy is a star disk

01:48:51 that extends over about 100,000 light-years

01:48:54 and is 1,000 light-years thick.

01:48:57 The Sun, its central star,

01:48:59 is located halfway from the centre of the galaxy

01:49:02 and near the centre of the disk in the vertical direction.

01:49:06 Leaving the galaxy, we would have to go further than its edge

01:49:10 to get away from the halo surrounding the Milky Way,

01:49:13 old stars, diffuse gas, and globular amas.

01:49:16 If you wanted to go even further to see the Milky Way in its entirety,

01:49:20 you would have to travel 48,000 light-years vertically.

01:49:23 At present, we don't even have a telescope that we could send there.

01:49:28 There are central stars that swallow up planets.

01:49:31 Our solar system is stable,

01:49:33 unlike many other planetary systems,

01:49:35 so we shouldn't be afraid that the Earth or another planet

01:49:38 will change its orbit and head for the Sun.

01:49:41 But at least a quarter of other planetary systems

01:49:43 with stars orbiting similar to our Sun

01:49:45 have a rather chaotic past.

01:49:48 In some of them, planets were moving

01:49:50 and their unpredictable migration

01:49:52 may have disrupted the trajectories of some other planets

01:49:55 or even pushed them out of their orbit.

01:49:58 This means that some planets

01:50:00 probably fell into the central star.

01:50:02 When this happens,

01:50:04 the planet dissolves in the outer layer of the star,

01:50:07 which means that it is swallowed up.

01:50:10 Imagine that you are an astronaut

01:50:13 who is racing through space in your last-ditch space ship.

01:50:16 But suddenly, you notice that you are running out of fuel.

01:50:19 What are you going to do?

01:50:21 Trapped in the middle of space?

01:50:23 It's not as if there were floating service stations everywhere.

01:50:26 The good news is that you won't be completely stuck.

01:50:29 A space ship will never really stop

01:50:32 after running out of fuel.

01:50:34 All because there is practically no atmosphere in space.

01:50:37 That's where the quote from the movie "Alien" comes from.

01:50:40 "In space, no one can hear you scream."

01:50:43 Sound travels through the vibration of tiny atoms and molecules.

01:50:46 In space, where there is no air,

01:50:48 there is simply no way for sound to travel.

01:50:51 It's the same for our space ship.

01:50:53 As there is no air,

01:50:55 there is also a total lack of air resistance.

01:50:57 The tiny particles that exist in space

01:51:00 are far too small to reduce the speed of a space ship

01:51:03 or to make it go backwards.

01:51:05 For this reason, most space ships turn off their engines

01:51:08 for most of their journey.

01:51:10 So don't believe those movies

01:51:12 that show space ships with their engines on all the time.

01:51:15 It's completely inaccurate.

01:51:17 Unlike ships in water,

01:51:19 a space ship doesn't need constant thrust to keep moving.

01:51:22 Usually, its engine is only on for very short periods.

01:51:25 It's not only practical,

01:51:27 but it also saves money.

01:51:30 Fuel is very expensive to transport in space because it's heavy.

01:51:33 That's why space ships try to use as little fuel as possible.

01:51:37 They need it when they leave Earth

01:51:39 and when they return to the atmosphere.

01:51:41 This happens when they need to slow down on their return.

01:51:44 While cars and trains have brakes,

01:51:47 it's not that easy to stop a space ship in a brutal way.

01:51:50 Engines are necessary to slow down the ship

01:51:53 or to stop it completely.

01:51:55 You need to strategically turn on impressive propellers at the front.

01:51:58 This creates the necessary resistance

01:52:00 and reduces the speed of the space ship.

01:52:03 But this process also requires very high levels of precision.

01:52:06 A wrong move can have dramatic consequences.

01:52:09 If you drive the propellers too fast,

01:52:11 the space ship will catch fire

01:52:13 as you enter the Earth's atmosphere at thousands of kilometres per hour.

01:52:17 Travelling too slowly can also cause problems

01:52:20 because in this case, you could completely miss the orbit of our planet

01:52:24 and go way beyond Earth.

01:52:26 And most space ships don't have enough fuel to try a second return.

01:52:31 So you have to avoid travelling too slowly at all costs.

01:52:35 But let's get back to the issue that concerns us.

01:52:38 This means that any vehicle with an empty tank

01:52:40 will continue to travel at the same speed in space

01:52:43 until it ends up hitting something.

01:52:45 There is simply no other way for it to stop.

01:52:49 But this may not be such good news.

01:52:52 If you're floating in space,

01:52:54 it's unlikely that your NASA mates will organise a rescue mission.

01:52:58 It may sound a bit sad, but it makes sense.

01:53:01 By the time they set up a new team

01:53:04 and find a ship to come and save you,

01:53:06 you'll have travelled so far that it would take them years to reach you.

01:53:10 It would also cost a huge sum of money.

01:53:13 NASA spends an average of $152 million

01:53:17 to launch a ship into space.

01:53:19 It's as much as buying six brand new luxury Lamborghinis.

01:53:22 Even crazier, NASA spent about $49 million

01:53:27 to develop and launch the first space shuttle.

01:53:30 Unfortunately, once you've left Earth's orbit,

01:53:33 it's almost impossible to return without fuel.

01:53:36 This is what happened to the NASA space probe Dawn in 2018.

01:53:40 On a normal day, the space ship ran out of fuel.

01:53:44 It then found itself completely stuck in the middle of space.

01:53:48 It stopped sending signals to Earth,

01:53:50 and finally set off on a 11-year mission

01:53:52 that had set a lot of space records.

01:53:55 The space probe couldn't produce electricity

01:53:57 because it ran out of fuel to move its solar panels

01:54:00 to direct them towards the sun.

01:54:02 And to this day, the space ship is still floating somewhere in space,

01:54:06 in a state of wreckage.

01:54:08 Fortunately, Dawn didn't have an astronaut on board.

01:54:11 The space ship began to orbit around the planet Nen Ceres,

01:54:15 which was the object it was originally studying.

01:54:17 An orbit is an incurved trajectory around a star,

01:54:20 a planet or a moon on which an object is stuck.

01:54:24 But NASA is an expert in everything that concerns space ships.

01:54:28 So how do they manage to let a ship run out of fuel?

01:54:31 In fact, it's very difficult to accurately measure

01:54:34 the amount of fuel we'll need in space.

01:54:38 On Earth, gravity holds all the fuel at the bottom of the tank,

01:54:42 and you can use a floating sensor

01:54:44 to measure how full the tank is.

01:54:47 But that's impossible in space,

01:54:49 because of the absence of this gravity, which normally weighs on the fuel.

01:54:53 Instead, a common approach is to add a bag of air

01:54:56 to the fuel tank, which is pressurized before launch

01:55:00 to push the fuel into the conduits.

01:55:02 The more fuel is used, the more this bag expands.

01:55:05 It takes up more space and maintains the fuel

01:55:08 at an adequate pressure level.

01:55:10 This pressure is controlled,

01:55:12 so you can know how much fuel is left.

01:55:14 As you can see, it's much more complicated than on Earth.

01:55:18 But let's say astronauts are on board a space ship

01:55:21 that has no more fuel.

01:55:23 How long could they survive?

01:55:25 Well, it depends on the amount of food and water on board.

01:55:28 NASA usually calculates the exact amount of food

01:55:31 astronauts need for their trip

01:55:34 to avoid adding extra weight to the space ship.

01:55:37 But the good news is that this food can technically be rationed

01:55:41 and its consumption can be extended.

01:55:43 This is because astronauts' food is packaged in a special packaging

01:55:47 that prevents it from getting spoiled.

01:55:49 There are no refrigerators on board space ships.

01:55:52 The food is presented in transparent and flexible bags

01:55:55 that can be opened with scissors.

01:55:57 All food is pre-cooked and transformed,

01:56:00 so it doesn't need to be stored in a refrigerator.

01:56:03 The only exceptions are fresh fruits and vegetables.

01:56:06 These are the only foods that need to be eaten quickly

01:56:09 because they spoil.

01:56:10 Today, astronauts also work with nutritionists

01:56:13 to choose the foods they like and will enjoy eating.

01:56:17 They can choose from a whole bunch of products,

01:56:20 including mushroom soup, cheese pasta, chicken, beef, ham, nuts,

01:56:25 and even delicious biscuits.

01:56:27 The shrimp cocktail is apparently astronauts' favorite

01:56:30 because of its spicy taste.

01:56:32 Aromatized drinks also exist in the form of powder,

01:56:35 just like instant coffee or Kool-Aid bags

01:56:37 that you have in the cupboard of your kitchen.

01:56:39 It's interesting to note that astronauts often declare

01:56:42 that they're not hungry in space.

01:56:44 So it's probably easier than we think to ration food.

01:56:47 But if we can make food last, what about water?

01:56:51 Carrying anything in space costs a lot of money,

01:56:54 and water is quite heavy, so its transport costs even more.

01:56:58 For this reason, water tanks cannot be constantly

01:57:01 dispatched into space.

01:57:03 Instead, astronauts have a very complex water system.

01:57:06 It allows each drop of liquid to be extracted safely and available to the environment.

01:57:10 This means recycling used water.

01:57:13 This means that our space buddies drink water that has been filtered

01:57:16 from shower water, from their breathing,

01:57:19 from the fuel cells of the spacecraft, from sweat, etc.

01:57:23 But don't worry, this water is drinkable

01:57:25 and even better than most of the water that comes out of the taps.

01:57:28 The water of a spacecraft first goes through a series of filters,

01:57:32 starting with the one that eliminates particles and debris.

01:57:35 Then it goes through multi-filtration beds

01:57:38 containing intelligent substances that eliminate impurities.

01:57:41 The last step is to get rid of harmful compounds

01:57:44 and destroy bacteria and viruses.

01:57:47 There are also emergency water tanks.

01:57:50 For example, the International Space Station has about 2,400 litres of water in its tanks,

01:57:55 just in case.

01:57:57 But what about air supply?

01:58:00 The main source of oxygen on board spacecrafts

01:58:03 comes from a process called water electrolysis.

01:58:06 It's an amazing system that uses the electricity

01:58:09 from the spacecraft's solar panels to separate water into hydrogen and oxygen.

01:58:13 But as we saw with the NASA's Dawn spacecraft,

01:58:16 without electricity it's quite difficult to direct the solar panels to the sun,

01:58:20 which means that the oxygen system would probably stop.

01:58:24 But there is still oxygen stored in a pressurized reservoir.

01:58:28 It's an emergency reservoir.

01:58:33 You fall directly into the black hole and prepare for a sad end.

01:58:37 Well, it's not so sure.

01:58:39 Falling into a black hole won't necessarily kill you or destroy your spacecraft,

01:58:43 but you'll have to choose a large black hole to hope to survive.

01:58:47 If you fall into a small black hole, its event horizon is too narrow

01:58:51 and the gravity increases by every centimeter downwards.

01:58:54 So if you put your arm forward,

01:58:56 the gravity at your fingertips will increase by a centimeter.

01:59:00 If you put your arm back, the gravity at your fingertips will be much stronger than at your elbow.

01:59:04 Your hand will lengthen and you will feel a certain discomfort,

01:59:08 or even an atrocious pain.

01:59:11 But it's not the same story if you fall into a supermassive black hole

01:59:14 like the ones in the center of galaxies.

01:59:17 They can be millions of times heavier than the sun.

01:59:20 Their event horizon is wide and gravity doesn't change that quickly.

01:59:24 The force you'll feel on your heels and at the top of your head

01:59:27 will be about the same and you'll be able to reach the center of the black hole.

01:59:30 And that's it, this myth has been deconstructed.

01:59:33 The next one claims that we can save the Earth from a giant asteroid

01:59:38 by making it explode first.

01:59:40 The scenario is as follows.

01:59:42 A spacecraft lands on the asteroid's surface.

01:59:45 A team of astronauts quickly drill a hole in it,

01:59:48 leave a trapped package and fly away.

01:59:51 And then, boom!

01:59:53 The asteroid will break into several pieces,

01:59:57 but will continue its race to Earth.

02:00:00 Big pieces will fall on our surface, causing big damages.

02:00:04 The mission is a failure.

02:00:06 To save the Earth, we need a big boom.

02:00:10 Not inside the asteroid, but just above its surface.

02:00:14 When the boom occurs, the force of the explosion

02:00:17 will push the asteroid slightly down.

02:00:20 Even a slight change in trajectory would be enough

02:00:23 for the asteroid to pass over the Earth.

02:00:26 Mission accomplished.

02:00:28 Oh, what if we caused a big boom on an asteroid?

02:00:32 We wouldn't be able to hear the noise.

02:00:34 In movies, we always hear the noise of spaceships and space battles.

02:00:38 But that's just a myth.

02:00:40 The sound is a wave that propagates because of the vibrations of the molecules.

02:00:44 A person applauds a few meters from you.

02:00:47 The sound wave starts to push the first air molecule next to the boom,

02:00:51 then the second, the third, and so on,

02:00:54 until the wave reaches your ear.

02:00:57 To propagate the sound, you need molecules like air or water.

02:01:01 In our atmosphere, sound waves propagate very well,

02:01:04 but space is a vacuum, so there is nothing.

02:01:07 You can tap your hands,

02:01:09 there will simply be no molecule capable of vibrating and transporting this sound.

02:01:14 Another myth about asteroids.

02:01:17 We'll have to go a little further than Mars.

02:01:20 We are in an asteroid belt,

02:01:22 and we must constantly avoid giant rocks and ice blocks.

02:01:26 We have entered a dense cloud of asteroids.

02:01:29 Uh, actually, no.

02:01:31 It turns out that space is huge, and the distances are incredible.

02:01:35 All the rocks and debris of the asteroid belt

02:01:37 only represent 4% of the weight of the Moon.

02:01:40 So there really isn't that much.

02:01:42 To understand the size of the vacuum in space,

02:01:45 let's take the case of the collision between two galaxies.

02:01:48 There are billions of stars in each of them.

02:01:50 If we mix them up, it is unlikely that there will be collisions.

02:01:54 Another myth is that zero gravity exists in our orbit.

02:01:58 Imagine that you are in a huge box 16 km in the air.

02:02:02 Now we drop the box and it starts to fall.

02:02:05 You fall at the same time as the box at the same speed.

02:02:08 And there, it's as if you felt zero gravity.

02:02:11 The same thing happens in orbit.

02:02:13 The International Space Station is located 400 km above Earth.

02:02:18 And it continuously falls, not on the surface of the planet,

02:02:21 but around it, in its orbit.

02:02:23 Its speed is about 7.6 km per second.

02:02:27 It could cross the United States from the west coast to the east coast in just 8 minutes.

02:02:32 Astronauts are experimenting the same thing.

02:02:35 They fall with the ISS at the same speed.

02:02:39 Now, let's look at the Moon.

02:02:41 It always shows us only one side.

02:02:43 Does this mean that the Moon has a dark side and that the sun's rays never reach it?

02:02:48 No, it's still a myth.

02:02:50 The fact is that the Moon is linked to the Earth by gravity.

02:02:53 There are days and nights there too.

02:02:55 But it turns out that this rotation is perfectly synchronized with that of the Earth.

02:03:00 So when you look at the Moon, you always see only one side.

02:03:04 Although there are days when the sun shines there too,

02:03:07 it's not the hidden side, but the opposite side.

02:03:09 We even have pictures of this place.

02:03:11 And we find one of the largest craters in our entire solar system,

02:03:15 the basin of the South Pole, Hyde Cane.

02:03:18 It is twice as wide as Texas.

02:03:21 One of the myths that has proven to be false

02:03:23 and that humans never went to the Moon.

02:03:26 Here is the original space suit of the first astronauts who went there.

02:03:30 Look at the sole of the shoe.

02:03:32 Some people claim that it is impossible that they could have left footprints like this one there.

02:03:37 In fact, yes, it is possible.

02:03:39 On the Moon, astronauts wore extra boots over their suits,

02:03:43 and their soles perfectly matched the footprints on the Moon.

02:03:47 The astronauts did not wear them when they left the Moon.

02:03:51 They also left a lot of things there.

02:03:53 They even tore the seats' cushions in the lunar module to reduce their weight.

02:03:57 Today, the total weight of human waste on the Moon is about 187 tons,

02:04:03 including several lunar rovers, debris from space ships, rocket floors and lunar probes.

02:04:09 It's the equivalent of three Boeing 737s.

02:04:12 The next myth concerns the summer.

02:04:14 It states that the hot season comes because the Earth is at its closest distance from the Sun for a year.

02:04:20 The Sun would then warm up our planet more, and it would be time to go to the beach.

02:04:25 This is not true.

02:04:27 Let's draw an axis across our planet.

02:04:29 It is slightly tilted to one side.

02:04:32 Winter comes when the axis of our planet is tilted away from the Sun.

02:04:36 But over time, the axis tilts towards the warm star.

02:04:39 Its rays then shine at an angle such that it is warmer.

02:04:43 It is true, however, that the Earth is at different distances from the Sun depending on the season.

02:04:47 This is because our orbit is not a perfect circle, but slightly flattened.

02:04:52 In other words, an ellipse.

02:04:54 Normally, the distance to our star is about 150 million kilometers.

02:04:58 But this distance can vary by 5 million kilometers depending on the point of our orbit where we are.

02:05:04 Another myth about the Sun is that it is yellow.

02:05:07 Let's take a closer look to see it.

02:05:09 You look out the window and ... it's white.

02:05:13 The Sun appears yellow only through the filter of our atmosphere.

02:05:17 The composition of the air and its thickness distort the star's light.

02:05:22 This is why stars exist in different colors.

02:05:25 The coldest stars have bright orange and red colors.

02:05:28 They are generally very old stars, older than our Sun.

02:05:32 But the young and very warm stars are bright blue.

02:05:36 The Sun is about in the middle of this spectrum.

02:05:39 You have also heard that if you remove your space suit in space, you will explode like a balloon.

02:05:45 Well, our bodies are designed to function under the pressure of the atmosphere.

02:05:49 But space is a void.

02:05:51 Imagine a huge metal barrel from which we sucked all the air it contained.

02:05:55 Add to this a temperature of -270 ° C and you get the conditions of space.

02:06:02 If you put yourself in these conditions, all the air pockets of your body, like your lungs for example, will begin to expand.

02:06:09 You could really explode like a balloon if your tissues were not so elastic.

02:06:13 But they stretch and bend, so you keep the shape of your body.

02:06:17 You will have enough oxygen in your body to last about 20 seconds.

02:06:21 Then your brain will start to lack oxygen and you will faint.

02:06:25 You will not explode and you will not even freeze, because you will be in the void that does not conduct the temperature.

02:06:31 Water conducts temperature very well, for example, so you feel the cold instantly,

02:06:37 while you feel better in the air at the same temperature.

02:06:40 If you are in the void of space, very low temperature will not be a problem for you.

02:06:45 Solar radiation is much worse.

02:06:48 On Earth, we have a shield against radiation, in the form of an atmosphere that blocks harmful rays.

02:06:54 In space, you will be defenseless.

02:06:56 Finally, between the absence of air, the cold temperatures and the radiation, you will really have only the choice.

02:07:03 Another myth is related to cell phones.

02:07:05 People think that when you make up the number of your friend, your phone sends a signal into space,

02:07:10 that there are a whole bunch of satellites that capture your signal and reflect it like a mirror directly into your friend's phone.

02:07:17 No, that's not true.

02:07:19 However, there are satellite phones in the world that work this way.

02:07:24 But when you make a call on a cell phone, your signal is transmitted by a cellular tower system from one to the other,

02:07:30 until it reaches your friend's phone.

02:07:33 you

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