Les scientifiques ont découvert beaucoup de choses sur ce qui se trouve à l'intérieur de la Lune, et c'est assez fascinant. Sous sa surface poussiéreuse se trouve un noyau interne solide, entouré d'un noyau externe liquide, tout comme la Terre. Mais voici où les choses deviennent intéressantes : contrairement à notre planète, la Lune n'a pas de champ magnétique pour la protéger contre les radiations solaires, ce qui explique pourquoi elle est si stérile et dépourvue de vie. Un autre fait intéressant est que la Lune s'éloigne lentement de la Terre à un rythme d'environ 3,8 centimètres par an. Et tenez-vous bien : il y a plus de 400 000 livres de déchets fabriqués par l'homme qui ont été laissés sur la Lune lors de diverses missions ! Et saviez-vous que la Lune a environ 4,5 milliards d'années ? Animation créée par Sympa.
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FunTranscript
00:00Well, I officially give up on the hope that the Moon is made of cheese.
00:05It's not even gouda.
00:07Our favorite ball, or curved banana, or half a coin according to the phase in which it is located,
00:13is composed of different layers, just like the Earth.
00:17And one of these layers is the internal core.
00:20About twenty years ago, scientists studied the rotation of the Moon.
00:24From their data, they concluded that it had a fluid external core.
00:28But the internal core was difficult to study.
00:31They did not know if it was solid like rock or fused like a hot liquid.
00:36But everything is clearer today.
00:38Astronomers were able to collect data during various missions,
00:42including the Apollo mission,
00:44during which the astronauts went to collect important information.
00:48They used a special technique to obtain seismic data.
00:52This consists of studying how sound waves move in objects.
00:57Take the example of seismic waves on our planet.
01:00When a seismic wave occurs, it creates waves in the ground.
01:04Scientists can detect and analyze these waves to learn more about them on our planet.
01:09The same idea can apply to other objects in our solar system,
01:13planets or, in this case, the Moon.
01:15When earthquakes or moons occur, they generate sound waves.
01:20By listening and studying these waves carefully,
01:24scientists can create a detailed map of what is inside the object.
01:28They can determine the different layers, their composition and their arrangement.
01:33To examine the interior of the Moon, we also used what is called laser telemetry.
01:39This method allows to measure the distance between the Earth's surface and that of the Moon.
01:44And it turned out that the internal core of our satellite is a dense and solid iron ball,
01:49just like that of the Earth.
01:51It measures about 500 km wide, which is about 15% of the size of the Moon.
01:56We also came across evidence that confirms the theory
02:00that the layer between the surface and the core, called the mantle,
02:04moved as the satellite evolved.
02:08This movement is called the lunar mantle reversal.
02:12And it explains why we find elements rich in iron on the surface of the Moon.
02:16The material of the mantle is transported upwards.
02:19And this volcanic rock then remains in the lunar crust.
02:22Some of the materials of this rock, being very dense,
02:25simply flow through lighter materials to the edge, separating the core of the mantle.
02:31It's like a cycle.
02:33The material of the mantle rises when the volcanoes are active,
02:36transporting elements rich in iron to the surface, then going down.
02:41There is another mystery that scientists have tried to solve.
02:46What caused the magnetic field of the Moon to weaken and almost disappear?
02:51Now that we have discovered the iron core and the mantle reversal,
02:55we will be able to get some answers about the magnetic field of the Moon.
02:59Knowing what the internal core looks like can help us better understand the history of the Moon,
03:04as well as that of our entire solar system.
03:08According to one of the theories widely accepted on the origin of the Moon,
03:12there would have been a massive collision between the Earth at its beginning
03:15and a mysterious object of our solar system.
03:18This is called the Big Impact Theory.
03:21This collision would have been so powerful that it would have torn a large piece of the Earth,
03:26then still in fusion.
03:28If you put a piece of 5 American cents next to a small green weight,
03:32you will have a good idea of the size of our planet compared to that of the Moon.
03:37This piece was then launched into orbit around our planet.
03:42And this would have happened about 95 million years after the formation of our solar system.
03:47The object that hit the Earth would have had a mass of about 10% of that of our planet
03:53and a size approximately equivalent to that of Mars.
03:56And yes, the Earth and the Moon have similar compositions, after all.
04:01Of course, there are other theories about the formation of the Moon.
04:05According to one of them, it would be the gravitational force of our planet that would have captured it.
04:10This means that the Moon was only passing through there when, suddenly,
04:14it was attracted to the orbit of the Earth.
04:17There is even a hypothesis that the Earth would have flown the Moon to Venus.
04:23If this is true, the Moon has nothing to complain about.
04:25The view is much better from here.
04:27So yes, the Moon and the Earth are similar in terms of rocks and certain minerals.
04:33But the Moon does not have the same atmosphere as our planet.
04:36Its atmosphere is fine and is composed of strange gases, potassium and sodium, for example.
04:42Which is quite different from the atmospheres of Mars, Venus or the Earth.
04:46And there is no water in the lunar rocks.
04:49But that does not mean that there is no water at all.
04:52During this century, astronomers have seen large dark spots on the surface of the Moon.
04:58One of these astronomers, Michael Van Langeren, thought that these spots looked like oceans.
05:03He therefore called them Maria, which means sea in Latin.
05:08Other astronomers have also drawn maps of the Moon
05:11and have also used the term Maria to describe these dark spots.
05:15For example, Mar Tranquillitatis translates as Sea of Tranquility.
05:20This is where Apollo 11 landed.
05:22But it turns out that these dark spots are not oceans at all.
05:26These are hard lava plains that rose to the surface a long time ago.
05:30Volcanic eruptions would have left behind them these smooth and flat areas called basalt plains.
05:36At the end of the 19th century, an observer, William Pickering,
05:40examined the Moon and discovered that it had no atmosphere.
05:44Without atmosphere, there are no clouds or air to prevent water from evaporating.
05:48Scientists therefore thought that if there was water on the Moon, it would have disappeared right away.
05:54In fact, they thought that the Moon was totally dry.
05:57But in 1961, a physicist, Kenneth Watson, had a different idea.
06:03It's night outside, almost 2 a.m.
06:06You go out to look at the sky, and here is the Moon, bright and full.
06:11You may think you know a lot about the Earth's natural satellite,
06:15but let me ask you the following question.
06:18How was it formed?
06:20The answer is that nobody knows.
06:23But of course, there are a few theories.
06:26The most widespread, called the Giant Impact Hypothesis,
06:29states that the Moon was formed during a collision between the Earth and another planet.
06:35This planet must have been smaller than ours, approximately the size of Mars.
06:40The collision itself would have probably occurred about 4.5 billion years ago.
06:47Another theory, called the Capture, states that the Moon was an asteroid or another wandering body.
06:53It would have formed somewhere in the solar system,
06:56and passing near the Earth, it would have been hit by the gravity of our planet.
07:01Except that there is a hitch.
07:03Our planet and the Moon have remarkable isotopic and chemical similarities.
07:09They must therefore have a common history,
07:11which means that the Moon could not have been created elsewhere.
07:15Other experts think that at some point in its distant past,
07:19the Earth was spinning so fast that part of its matter would have detached.
07:23It would have quickly been put into orbit around our planet,
07:27and thus the Moon would have appeared in the sky.
07:30But again, there is a problem.
07:33In this case, the type of minerals present on the Moon,
07:36as well as their proportions, should be the same as on Earth.
07:40However, there are slight differences.
07:42The Moon is rich in materials that would have formed very quickly at high temperatures.
07:47There is another theory, probably the least exciting.
07:51It claims that the Earth's natural satellite could have simply appeared at the same time as the Earth during its formation.
07:58But today, a more pressing question concerns astronomers.
08:02Is the Moon really the Earth's satellite?
08:06Or are they two twin planets?
08:09The Moon is of considerable size compared to our planet.
08:12It represents about a quarter of the size of the Earth.
08:15This is why some experts qualify our planetary system as a double planet.
08:19But to what extent is this exact?
08:22To find out, we must first define the word planet.
08:25According to the International Astronomical Union,
08:28a planet is a spatial body in orbit around a star.
08:32Massive enough to have an almost round shape,
08:35thanks to its gravity, which has released the region around its own orbit.
08:39Now, what is a satellite?
08:42It is a spatial body in orbit around a larger body.
08:46If we take the Earth-Moon system,
08:48its center of gravity, called the barycenter, is inside the Earth.
08:53This is why, at present, we cannot really say that we live in a system of double planets.
08:59According to this definition, the Moon is therefore the satellite of our planet.
09:04Let's go back a little.
09:063 or 4 billion years ago,
09:08even if the Moon was not a planet,
09:10it probably had a real atmosphere.
09:14It was formed when powerful volcanic eruptions shook our satellite.
09:19Gases spread over the entire surface of the Moon,
09:23and this happened so fast that they did not have time to escape into space.
09:28At this time, the lunar surface was full of pools filled with volcanic basalt.
09:34Imagine huge amounts of magma projected into the air,
09:37falling back on the ground and creating lava flows.
09:41This is how these basalt pools appeared on the surface of the Moon.
09:45Upon Apollo 11's return,
09:47scientists were finally able to get their hands on samples from our satellite.
09:52They discovered that the lava flows contained not only carbon monoxide and sulfur,
09:57but also the constituent elements of water.
10:00Thanks to these samples,
10:02researchers were able to calculate the amount of gas that had risen to form this atmosphere.
10:07It was the densest about 3.5 billion years ago,
10:11and will have persisted for about 70 million years.
10:14After that, it dispersed into space.
10:17But the most surprising thing is that when the Moon had an atmosphere,
10:21it was also 3 to 10 times closer to our planet.
10:25A computer simulation even suggests that the Moon was probably up to 19 times closer than it is today.
10:32The distance that separated it from our planet could have been 30,000 km,
10:37while today our satellite is about 384,000 km.
10:42Thus, the Moon seemed much bigger in the sky.
10:46But alas, at the time, there were no dinosaurs to admire the view.
10:51Nowadays, the atmosphere of the Moon is almost non-existent.
10:55This is why the satellite cannot protect itself from meteorites,
10:58and the surface of the Moon is littered with craters.
11:01For comparison, there are about 190 identified impact craters on our planet.
11:07Many of them are hidden by vegetation or covered with water.
11:11But if we talk about the Moon, their number is much larger.
11:15There are several million of them,
11:17and about 5,000 of them measure more than 19 km in diameter.
11:21As the Moon is geologically less active than the Earth,
11:24these craters and other ancient formations have been in perfect condition for centuries.
11:30When you look at the Moon, it is the brightest object in the night sky.
11:34But in reality, its surface is rather dark,
11:37because the reflection factor of our natural satellite is just a little higher than that of the asphalt.
11:43At the time of the Apollo missions,
11:45astronauts who came back from the Moon claimed that the lunar dust,
11:48this gray dust, similar to sand,
11:50which covers a large part of the surface of the satellite,
11:53smelled, and tasted, yes, they really tasted it, gunpowder.
11:57But the lunar dust has nothing to do with gunpowder.
12:00About half of its composition is vitrified silicon dioxide,
12:04coming from meteorite impacts.
12:06It hits the surface of the Moon at incredible speeds.
12:09Wow!
12:10The elevated temperature turns the ground into glass,
12:12and the impact breaks it right after, creating this gray and sticky dust.
12:18The rest of the ingredients of lunar dust are minerals such as iron, calcium and magnesium,
12:23while gunpowder in the old days consisted mainly of sulphate, coal and sulfur.
12:29In other words, the lunar dust should not smell like gunpowder, but it does.
12:34By the way, when the astronauts brought samples back to Earth,
12:37there was no smell at all.
12:40One explanation could be that the lunar surface is somewhat similar to the sand desert on Earth,
12:45like the Sahara.
12:47It is extremely dry and arid.
12:48When you breathe in the air in a desert, you don't smell anything.
12:51But if you are surprised by the rain there,
12:53the humidity will bring back all kinds of smell from the ground,
12:56which was previously trapped in the dry sand.
12:59Something similar could happen with lunar dust.
13:02When it is on the surface, it doesn't smell at all,
13:05even if the astronauts couldn't smell it with their space suits, of course.
13:09But when it was brought back to the Alunissage module,
13:12the dust came into contact with the humidity of the air and began to emit its strange smell.
13:17Another reason for this could be a reaction of the lunar dust to the solar wind.
13:21The sun's ionized particles hit the surface of the moon and stay there.
13:25There is no thick atmosphere to protect it from these ions,
13:29so that they travel freely to the ground.
13:32They are very light and can fly away at the slightest impact.
13:36Thus, when the astronauts brought these lunar dust samples
13:39aboard the Alunissage module,
13:41the particles could begin to move and release this specific smell.
13:46This could also explain why these samples didn't keep their smell
13:49when they were brought back to Earth.
13:51As these particles are so light,
13:53they were able to escape from the samples as soon as they were brought aboard the module
13:56and when they were placed in hermetic containers,
13:59there was little or no ion left on them.
14:01Another explanation is that these hermetic containers
14:04were not so hermetic after all.
14:06The lunar dust is essentially composed of very small crystals
14:09with extremely pointed edges.
14:11Against all odds, they would have made tiny notches in the seals,
14:14leaving between the air and the humidity,
14:16and the ionized particles would have escaped from the containers.
14:19Scientists think they should study this dust on the surface of the moon itself
14:23in order to understand its properties.
14:26There are hundreds of thousands of craters on the surface of the moon
14:29produced by the fall of asteroids,
14:31but one of them has attracted a lot of attention.
14:34It turned out to be not only an impact crater,
14:37but also a tube resembling the entrance of a network of caves.
14:41Scientists have detected a specific echo shape
14:44suggesting that a hollow area was below.
14:47They have also discovered echoes similar to those
14:49in a few places near the hole.
14:51So there could be other lunar tubes.
14:53But this one, in this case, could welcome an entire football field.
14:58Researchers think the surface could house a vast geological world.
15:02It could be a good shelter for astronauts landing on the moon,
15:06or even a future port due to a lunar colony.
15:09No one has ever managed to stay on the moon for more than three days
15:12due to the conditions that reign on the satellite.
15:15Extremely variable temperatures, a low atmosphere,
15:18no magnetic field to protect life from things like radiation or solar wind.
15:22Astronauts wear space suits,
15:24but they cannot protect them for long periods.
15:27A lava tube could.
15:29When a lava flow cools, it covers itself with a hard crust
15:32which then thickens and creates a dome above it.
15:35It continues to flow, but when it stops, the channel can finally empty.
15:39And that's how a hollow tube appears.
15:42Our planet also has lava tubes,
15:44but they are not as large as those found on the moon.
15:48In 1178, I was not yet born,
15:51but at least five people in England claimed to have seen the moon split in two
15:55from its upper edge.
15:57It had the shape of a crescent at the time of the event.
16:00When the split widened, fire began to come out.
16:03The monk who made the chronicle describes it as follows.
16:06A flame-lit grass burned, spitting fire, burning coal and sparks.
16:11Then the moon began to move and throb.
16:15But it quickly stopped and took on a slightly darker shade.
16:18The event, however, did not receive much attention from scientists
16:22before the second half of the 20th century.
16:24Researchers studied this chronicle and discovered
16:26that there was a huge crater 22 km wide on the surface of the moon,
16:30about where it is written in the manuscript.
16:33Only a very large asteroid could have left such a mark on the face of the satellite.
16:37And when they examined it more closely,
16:39they discovered that it was quite recent for a cosmic event.
16:43In fact, it could have appeared about 800 years ago.
16:48But in this case, millions of fragments of the asteroid and the moon
16:52would also have hit the Earth.
16:54And people would then have witnessed an incredible meteor shower.
16:57It would have been very bright,
16:59and the memories of this rain would certainly have been consigned to the archives.
17:03But this did not happen.
17:05In addition, many scientists claim that this crater is not as young as it seems.
17:09The most widespread and plausible theory is that it is between 1 and 10 million years old.
17:14If it had appeared as recently as 800 years ago,
17:17some parts of the surface of the moon, inside and around the crater,
17:21would have been still hot because of the impact.
17:24The most probable explanation of what really happened in 1178
17:28is that the observers were lucky enough to see an asteroid fall to Earth
17:32and burn in the atmosphere of our planet.
17:35The spectacle would have been incredible.
17:38And seen from a certain angle, the explosion of the asteroid
17:41could have really given the impression that it was the moon that was erupting.
17:44This would explain why there are so few witnesses of the phenomenon.