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00:00Imagine an alien world. A scorched, barren landscape, hot enough to boil water,
00:10where mysterious holes on the battle-scarred surface host a labyrinth of tunnels,
00:17each wide enough to house a city. This world is dead.
00:23Yet it breathes life into its nearest planetary neighbour.
00:28This extraterrestrial place is closer than you might imagine.
00:32This is our moon.
00:50Look at our solar system from an alien visitor's perspective.
00:56What would surprise you?
01:00What would make you look twice?
01:04The intriguing answer?
01:07Our oversized moon.
01:11If you look at our moon and compare it to all of the other moons in our solar system,
01:15it's actually quite odd.
01:18It's huge. Way bigger than any other moon in the solar system compared to its planet.
01:24It's a giant moon. It's almost like we're a binary planet,
01:27two objects orbiting around each other to some degree.
01:32Our planet-sized moon is unique in the solar system.
01:37And this battle-scarred giant serves as our guardian angel.
01:42Its immense gravity raises the tides that breathe life into the Earth's oceans.
01:48The moon stabilizes the tilt of our planet, regulating the climate and seasons.
01:56Without the moon, humans may never have evolved.
02:02We owe everything to our moon.
02:05Yet its formation is one of the greatest unsolved mysteries of planetary science.
02:18There are many theories for the origin of our supersized moon,
02:22but they all start the same way,
02:25with the formation of the inner solar system 4.6 billion years ago.
02:30When the solar system first formed, it would have looked very different from the way it looks now.
02:35Instead of having a few planets and mostly empty space surrounding the sun,
02:39you would have had a disk, and this disk would have been thick.
02:43It would have been composed of gas and dust and rocky bodies.
02:51The infant sun sparks into life, blowing away the clouds of gas that are closest to it.
02:59Over time, the rocky fragments that are left behind clump together to form dozens of new planets,
03:06many more than we now see today.
03:10The fledgling worlds jostle for position, crossing paths as they struggle to find stable orbits.
03:20Is it possible that one of these planets was destined to become our moon?
03:27There have been a lot of ideas about where our oversized moon came from.
03:32One idea was just that it was wandering around in our solar system, and we captured it.
03:41According to the capture theory, a wayward planet passed a little too close to the early Earth,
03:47and our planet's immense gravity seized hold of it.
03:53The planet then settled into orbit around the Earth and became the moon we see today.
03:59This theory seemed to tick all the boxes.
04:03But scientists needed proof.
04:07If it was really true that the moon was a captured planet,
04:10you would expect that its constituents would be different than the Earth.
04:13It was something that formed in a different place on the Earth and then got captured,
04:16so you would expect them to be made of different stuff.
04:20To prove the theory, scientists needed to compare the moon's earliest rocks with similar samples found on Earth.
04:28The best rock for comparison is anorthosite,
04:32a volcanic rock that could only have formed when the newly born moon was still molten.
04:39On Earth, anorthosite forms in highly geologically active places, like Iceland.
04:46This is what we want.
04:48You see this anorthosite, how white it is?
04:51Anorthosite forms in a different way than normal basalt.
04:55You can almost think of it like the white phone on the head of a dark beer, sort of floating up to the top.
05:01So in a magma environment, this would form and then just float up to the top of a magma sea.
05:10Getting a sample of anorthosite from the moon was crucial,
05:13because darker rocks could have had their chemistry altered by asteroid impacts.
05:18We really had to have a piece of this anorthosite rock,
05:21because we just couldn't learn about the origin of the moon from the dark materials.
05:26We had to have that genesis rock to tell us about the origin of the moon.
05:34In the 1970s, Apollo astronauts collected samples and brought them back to Earth for comparison.
05:41The results shocked the scientific world.
05:46What they found was that the composition of the moon was almost exactly the same as the composition of the crust of the Earth.
05:52This idea that the moon was a captured planet from elsewhere in the solar system was out.
05:56There was no way that was true.
05:58The rocks looked very Earth-like in many respects, and that was a puzzle.
06:06With the captured planet theory blown out of the water, planetary scientists went back to the drawing board.
06:13Scientists said, look, we've got to get together and figure this out.
06:16And they went to a conference together in Kona, Hawaii, all the top scientists in planetary science,
06:21and they hammered out all of the leading ideas.
06:24A lot of people think scientists don't have an imagination.
06:26We're just robots looking at things and analyzing, and it's not like that.
06:29If you want to figure out how something like the moon came to be,
06:33you have to have a wild imagination and try all these crazy ideas.
06:36But they have to be constrained by reality.
06:41They locked themselves into a room together and emerged from that meeting and said, yes, this can work.
06:47Scientists switched their attention to the water content of the moon rocks.
06:51They were surprisingly dry.
06:54Something must have heated up the moon to unimaginable temperatures,
06:57and we were led to think that it must be some sort of collision.
07:02A new theory emerged around the possibility of a catastrophic collision 4.5 billion years ago.
07:11But it wasn't an impact into the moon.
07:14It was an impact into the Earth.
07:19There was a crazy idea that the Earth formed, and while it was still young,
07:25another planet-sized object, something about the size of Mars, came in and hit the Earth.
07:33Blew off a huge amount of material, which then coalesced and formed the moon.
07:38This is a pretty cool idea. It was groundbreaking, I guess, literally.
07:43Scientists named the Mars-sized planet Theia and modelled how the impact would have played out.
07:524.5 billion years ago, Theia clips the Earth with a glancing blow.
07:59The impact throws molten debris far into space,
08:03forming a ring of burning rock around the Earth.
08:08If we could travel back in time and somehow stand on the surface of the Earth when the moon was forming,
08:13it would have been amazing.
08:15A bright ring of fire was stretching across the sky,
08:19and here in the sky would have been a bright ball of magma glowing,
08:24with all kinds of shrapnel and small rocks being attracted to that point
08:28because of the immense gravity.
08:30This was the proto-moon, the thing that would eventually become the moon we have in our sky today.
08:42Our moon forms in under a year.
08:46Its crust is almost chemically identical to Earth's, because they share a common origin.
08:52This impact idea, as weird as it sounds,
08:56actually does the best job explaining everything that we see about the moon.
09:03The impact hypothesis becomes the leading theory for the origin of our oversized moon.
09:10But when space probes journey to the far side of the moon,
09:14they discover something that throws the theory into chaos.
09:19The moon has a dark secret.
09:23The moon has a dark secret.
09:26It was born with a twin.
09:38Take a look at the moon tonight,
09:41and you might see a face,
09:43or perhaps a rabbit,
09:45or a tree, depending on your culture.
09:49Myths and legends surround the patterns etched on the surface of the moon.
09:53But what can these marks tell us about the origins of our oversized guardian?
09:58What we call the man in the moon is actually just a series of light and dark patches on the moon's surface.
10:04And, of course, people are programmed to recognize faces everywhere,
10:09so that's why we see this, you know, face.
10:11These dark patches appear to be unique to the moon.
10:16Centuries ago, astronomers thought they were seeing enormous oceans of liquid water.
10:21We now know the dark stains are actually ancient floods of volcanic lava.
10:28Planetary geologist Janie Radebaugh captures a bird's eye view of similar features on Hawaii,
10:34using her research kite cam.
10:37These lava flows we're standing on are identical to the things we would see
10:41if we were standing on the dark patches of the moon.
10:45They are dark in color, they're made of basalt,
10:49and they float out in vast lava flows across the surface.
10:53It turns out the dark planes of lava on the moon are battle scars.
11:01Evidence of a violent past.
11:04Four billion years ago, asteroids rained down on the newly formed moon,
11:09tearing into the surface.
11:12Where the fractured crust is thinnest, molten lava seeps from the moon's hot interior,
11:19spreading out in giant pools,
11:23and solidifying to form the scars we see today from Earth.
11:34Strangely, although the moon rotates, the Earth's gravity holds onto it so tightly,
11:40the same face points towards us at all times,
11:45making the features on the far side of the moon a complete mystery.
11:51For all of history, the far side of the moon was invisible to the Earth.
11:56It's the back side, you can't see it.
11:59In 1959, the Soviet spacecraft Luna 3 flew past the moon's far side
12:05and photographed it for the first time.
12:10Astronomers expected to see the same familiar dark and light patches,
12:15but they were in for a big surprise.
12:18When scientists saw the pictures, they were shocked.
12:22The far side looked completely different than the near side.
12:26It's saturated with craters.
12:28It just was such a huge dichotomy.
12:31Nobody was expecting that at all.
12:36The far side still had massive impact craters,
12:40but it was uniformly pale.
12:44It seemed like no dark lava had bled out onto the surface at all.
12:49But why?
12:51The only solution we could come up with is there's a difference in thickness
12:55between the crust of the near side and the crust of the far side.
12:59The back side must be so thick that lavas are not able to come up through them
13:04and erupt out onto the surface.
13:06Instead, on the front side, where it's very thin,
13:09lavas can easily come up through cracks and flow out onto the surface.
13:13Recent NASA missions confirm the crust on the back of the moon
13:17is around 26 kilometres thicker than the crust on the front.
13:21The far side is thicker. It's not like, oh, part of it is and part of it isn't.
13:25No, really, the other side of the moon has a thicker crust than the near side.
13:29That's bizarre.
13:34So one of the biggest mysteries in planetary science over the last 50 years
13:38is why is the crust of the far side so thick?
13:43The impact theory doesn't really cover that. It just forms the moon.
13:47But it doesn't say why one side should be so different than the other one,
13:51unless something strange happened.
13:56The new age of supercomputer modelling
13:59brought about the first credible explanation.
14:03The impact of Theia could have made two moons, not one.
14:09And this double birth might also explain our double-sided moon.
14:18According to the theory, 4.5 billion years ago,
14:21there were two moons in the night sky.
14:24The smaller moon chases its larger sibling, gradually getting closer.
14:30Eventually, the two moons collide and slowly meld together.
14:38The smaller moon covers the far side of the larger moon,
14:42creating a new, much thicker crust.
14:46Not all impacts are high-speed, super-violent events
14:50that eject material everywhere.
14:52Instead of just wham, smacking into it, it would have just merged with it,
14:57just been pulled apart and smeared out over the moon.
15:01Essentially, when you look at one half of the moon,
15:04you see more of one body, and when you look at the other side of the moon,
15:08you see more of the other body.
15:10They kind of wrapped around the first body and so it's thicker on that side.
15:16Two moons become one.
15:19The evidence for this cosmic collision seems to add up.
15:24Inside supercomputers, at least.
15:27But not all astronomers are convinced.
15:30Some believe there's an alternative explanation.
15:34And their proof lies on an alien planet that's being cooked alive.
15:47480 light-years from our solar system,
15:50a rocky, Earth-like planet orbits a sun-like star.
15:55But this is no place for life.
15:59Coro 7b is a sun grazer.
16:04This bizarre exoplanet orbits 60 times closer to its star than the Earth does to the sun.
16:11Their close proximity locks one face of the planet to its fiery companion,
16:16just like the moon is locked to the Earth.
16:20The result is a cosmic barbecue.
16:24Temperatures soar to over 1600 degrees Celsius on the near side of the planet,
16:30reducing the rocky surface to a boiling ocean of liquid magma.
16:35By contrast, the shaded far side of the planet has a cool, solid crust.
16:43This overcooked exoplanet is the inspiration for a surprising new theory
16:48about the formation of our moon's lopsided crust.
16:52It's the brainchild of a pair of young researchers with no background in lunar science.
16:59Because I work in exoplanets,
17:01I knew very little about lunar geology when this whole thing started.
17:06In 2011, Jason Wright was discussing sun-grazing exoplanets with colleagues,
17:12when conversation turned to the mystery of the moon's half-and-half crust.
17:18And then I remembered that the moon, when it formed, was very close to the Earth,
17:22and the Earth would have been extremely hot after the impact that formed the moon.
17:31And in fact, the geometry is almost exactly the same as the Corot 7b system.
17:36That got me thinking, well, maybe something similar happened to the moon.
17:42Jason theorizes that the hot Earth cooked the near side of the moon,
17:46just like stars cook sun-grazing planets.
17:51So if you imagine that the moon is forming,
17:53this big hot ball of the Earth is hanging in its sky,
17:56on the far side of the moon, it would be quite cool.
18:00The near side of the moon is kept hot by the molten Earth.
18:05Vast clouds of mineral vapor stream from the hot surface,
18:09feeding a cloud that surrounds the moon.
18:12On the cool side, these minerals condense and rain down, building a thicker crust.
18:20It's a nice idea, but it only works if the moon locks one face to the Earth straight after it forms.
18:29Jason asked grad student R. Peter Roy to see if that was even possible.
18:34When Jason first came to me with the idea, he was very excited about it,
18:38and he believed it was a big deal.
18:40The calculation to check the tidal locking of the moon was pretty easy to do.
18:45The number was so small that we were surprised.
18:48It was on the order of 100 days, which is very, very quick in astronomical timescales.
18:57R. Peter's breakthrough means that the near side of the moon
19:01locked to the Earth while our planet was still molten,
19:04supporting Jason's theory of a cooked moon.
19:07It's still very new, but the theory is gaining momentum.
19:12In science, if you have two ideas that explain something equally well,
19:16you kind of want to go with the one that has more natural outcome.
19:20This broiling Earth idea is a natural outcome of what we know must have happened.
19:28Thankfully for us, the surface of the Earth is a lot cooler today,
19:32but the inside is still hot, thanks to the radioactive decay of metals
19:36deep inside the core of the Earth.
19:40This rising heat drives the volcanism and geological activity
19:44we see on the surface today.
19:47There are mountain ranges being pushed up
19:49and other mountain ranges being subducted into the ocean.
19:51The crust of the Earth is continuously changing.
19:55The moon doesn't have a radioactive decay,
19:58so scientists have always assumed that its centre is cold
20:02and its geology is dead.
20:05But a series of unexplained observations suggest that, once again,
20:09we're wrong about the moon.
20:15One of the big questions we've been trying to answer over the last few decades
20:18is, is there any activity on the moon left at all?
20:22For hundreds of years, the moon has been the center of all life.
20:27For hundreds of years, astronomers have reported
20:29strange bursts of light coming from the moon.
20:33Others have witnessed reddish glows that lasted for minutes at a time.
20:39Could these rare sightings show that the moon's geological heart is still beating?
20:46The moon is small enough that, over four billion years,
20:49it should have cooled all the way through.
20:52And yet, there's still some things that we see
20:55that maybe kind of sort of indicate that there's still stuff going on inside of it.
21:01Aristarchus is a volcanic region in the northwest of the moon's near side.
21:08Astronomers have reported over 700 glowing lights here in the last 50 years.
21:16Even Neil Armstrong saw something strange here
21:19from the window of the Apollo 11 lander.
21:45What's going on in Aristarchus?
21:48Smoking volcanoes like this one in Hawaii
21:51have given planetary scientists a potential answer.
21:55Because where there's smoke, there should be fire.
21:59You know, one clue to how these events are happening on the moon
22:03is where they're found.
22:05They're actually found in a very special location on the moon
22:08and it's very much like what we're standing on right now.
22:11Aristarchus is covered in vast plains of volcanic ash
22:15and some scientists believe this fine material
22:18is responsible for the strange bursts of light we see from Earth.
22:24Now, the kind of ash that I'm holding right here is a little bit damp
22:27because there's been a recent rainfall in the region
22:29whereas the material we'd be holding at Aristarchus would be extremely fine.
22:34Gases escaping from this active volcano
22:36carry particles of fine volcanic ash and steam into the air.
22:41Sunlight brightens the plume, making it visible for miles.
22:46Perhaps something similar could happen on the moon.
22:48There's gas that comes out of the vent,
22:50picks up the very fine lunar dust
22:52and spreads it out across the landscape
22:54so that we can see it illuminated by sunlight.
22:57If the theory's true, it means the moon's volcanoes
23:02are still active.
23:04Something like this is just kind of so mind-boggling
23:07that it's hard for us to wrap our minds around the fact
23:09that the moon actually could still be alive today.
23:13I mean, we've thought for many years that the moon is cold and dead
23:16but maybe these are happening now
23:18and that means that the moon is not dead, the moon is alive.
23:22That's very exciting.
23:25We thought we understood the moon.
23:29But each time scientists peel back the layers, they find another secret.
23:33And perhaps the biggest of all
23:36is that without the moon, we wouldn't be here.
23:53The moon and the Earth were born together.
23:58They have dramatically shaped each other's evolution.
24:01And we now think that life too was given a head start
24:05by the presence of our oversized moon.
24:09This is the Earth 4.4 billion years ago,
24:13around the time scientists think life on Earth got started.
24:20The newly formed moon sits just 24,000 kilometres away,
24:25appearing much larger in the sky than it does today.
24:29Its gravity raises enormous tides in the Earth's warm, young oceans.
24:36In that era, the tides were not measured in feet, they were measured in miles.
24:41You'd have these massive tsunamis that would wash up on land
24:45and then wash back into the sea.
24:52The moon's gravity creates tides by drifting the atmosphere.
24:56Gravity creates tides by drawing Earth's oceans up towards it
25:01in a bulge of water.
25:04And as the Earth spins, this bulge washes onto land as a tide.
25:09The closer the moon, the bigger the pull of gravity
25:13and the stronger the tide.
25:16Some scientists think that the warm rock pools
25:19these giant early tides left behind
25:21are the perfect mixing bowl for the ingredients of life to come together.
25:27The good thing about a tidal pond is that environments change.
25:31Water comes in, brings nutrients, goes away, the nutrients concentrate.
25:35So that may have been a process that concentrated the stuff life needed
25:40in a way that led to life.
25:434.4 billion years ago, onrushing tides stirred up organic molecules
25:49from the surface of the Earth.
25:52As the tides receded, these chemicals were left behind in shallow rock pools
25:57which then evaporated in the heat of the sun,
26:00concentrating their chemical contents.
26:03And perhaps the first life was born inside this rich,
26:08If we had tiny little moons around the Earth like Mars does,
26:12then we never would have had the massive tides that carry materials
26:16and energy up onto the beach environment
26:19where life really might have gotten a foothold.
26:22And so we wouldn't have had the minerals, we wouldn't have had the energy,
26:26and maybe we wouldn't have had life.
26:30Did the moon create life on Earth?
26:33The jury's out, but one thing is certain.
26:37Intelligent life takes time to evolve,
26:40at least 4 billion years in our case.
26:44We've gradually changed from simple, single cells
26:48to the kind of organism that can question its own origins.
26:52And it's the moon that's provided the stability for life to evolve
26:57and for life to evolve.
26:59And it's the moon that's provided the stability for life to evolve
27:03by holding the Earth's axial tilt steady for over 4 billion years.
27:09The moon locked that tilt into place
27:12and has actually stabilized our rotational axis
27:15and made sure the seasons are mostly the same,
27:18century after century, millennia after millennia.
27:21When we look at the tilt of the Earth, it's been about the same
27:24for the time that complex life has existed.
27:26And this is really important.
27:28As we progress out of single-celled, simple organisms
27:31to much more complex organisms, greater stability really helps that.
27:35How different would things have been without the moon?
27:39Just look at Mars to see the devastating effects of an unstable tilt.
27:45Mars actually had a tilt that is as far as 60 degrees.
27:49That means that there was actually, it was cold at the equator on Mars
27:53and it was warmer at the poles.
27:54So that's really a difficult environment for life to arise and grow.
28:01When we look at Mars, we see that its axial tilt has swung around
28:05to such a degree that it's inhibited life.
28:09If the Earth had swung that chaotically,
28:12ice ages would have come and gone like seasons.
28:16Life would have needed to start from scratch, over and over again,
28:21never having time to evolve into complex organisms.
28:27Mars serves as an indicator that our supersized moon
28:31may have been instrumental in the development of intelligent life on Earth.
28:36And increasingly, scientists believe similar cosmic partnerships
28:40are the key to finding other intelligent life in the universe.
28:44When we're looking at exoplanets and we're wondering
28:47which one of these could have civilizations, advanced life forms,
28:51and there was a bunch that had a big moon and a bunch that didn't,
28:54well, I would say let's first look at the ones with the moon.
28:57If for no other reason, we know that on this world,
29:00we have a big moon and we have advanced life.
29:03As we're looking out beyond our solar system,
29:06we're looking into the galaxy, looking for exoplanets that might be habitable.
29:10Maybe we should be looking for an object that has a supersized moon
29:14in the right location around its star.
29:16It just might be the perfect place to look for life.
29:22Scientists have discovered over a thousand exoplanets
29:25orbiting stars in our galactic backyard.
29:30By measuring the dip in brightness
29:33as the planet passes in front of its parent star.
29:40An exomoon should also cause a tiny extra dip in brightness.
29:47Current technology can't pick out this double dip.
29:51But a future generation of space telescopes
29:54could potentially reveal large moons in the Milky Way.
29:59And perhaps then we'll be able to narrow down our search for a second Earth.
30:05If we ever want to see these distant exoplanets up close,
30:10we'll need a cheap, reliable route into space.
30:14And the moon could be the key to making this dream a reality.
30:19One of the greatest barriers to conquering space
30:23is the enormous amount of fuel required to escape Earth's gravitational pull.
30:29But the moon's gravity is six times weaker.
30:33A lunar launch pad could become a gateway to the stars.
30:38So if we establish a base on the moon, for example,
30:42now we need very little energy to get off of the moon
30:45and to go and explore other bodies from there.
30:49What would it take to build a lunar Cape Canaveral?
30:54The biggest hurdle is keeping the ground crew alive.
31:00One of the biggest dangers of being on the surface of the moon
31:03is you're not protected by a magnetic field.
31:05On the moon you don't have that.
31:07If there's a big solar storm, the flux of high energy particles,
31:10it would hit astronauts with so much energy
31:12they would break down the cells and destroy our DNA.
31:15The moon is also hit with radiation
31:18that originates from far outside our solar system.
31:22Distant supernovas throw out charged particles called cosmic rays
31:27at close to the speed of light.
31:33On Earth, our atmosphere blocks most of the incoming rays.
31:38But on the moon, astronauts are in the firing line.
31:43And many have reported seeing tiny flashes
31:46as cosmic rays smash through their optic nerve.
31:58Incoming space rocks are another major hazard on the moon.
32:02On the moon there's no atmosphere.
32:04So something the size of a grain of sand
32:06is moving at speeds multiple times the speed of a bullet.
32:11And if that hits your colony,
32:13it can put a pretty good hole in the wall.
32:18Yet another obstacle to long-term survival on the moon
32:22is the extremes of temperature.
32:25One of the things we don't really think about,
32:27about the air around us, is that it actually redistributes heat.
32:30On the moon you have no air.
32:32So if you have your hand and half of it is in sunlight
32:34and half of it is in shadow,
32:36you've got a 400 degree difference there.
32:41The best protection from all of these long-term problems
32:44is a thick layer of rock.
32:47But a recent discovery suggests
32:50future astronauts won't need to dig
32:53to build their shelters underground.
32:56This remarkable hole on the surface of the moon,
32:59called a skylight,
33:01is the size of a football pitch.
33:04We are seeing big openings to massive cave systems
33:09that might form the perfect base for lunar exploration.
33:13And we're going to find out
33:15what those openings are going to look like.
33:18We're going to find out
33:20what those openings are going to look like.
33:22And we're going to find out
33:24what those openings are going to form
33:26the perfect base for lunar exploration.
33:29Skylights are the entrances to a network of vast tunnels
33:33which potentially run for miles under the surface of the moon.
33:37There are already underground caverns there,
33:41and they're not carved by water.
33:43These are carved by lava.
33:46Similar natural tunnels, called lava tubes,
33:49are found in regions like Iceland.
33:57So we're in the bottom of a hole
34:00that's formed from a collapsed lava tube.
34:03Now, we know that on the surface of the moon
34:05there are holes like this.
34:07And if all indications are correct,
34:09they also lead to giant lava tubes just like this one.
34:14Lava tubes form when flowing rivers of molten rock
34:17start to cool.
34:20The surface solidifies first,
34:22insulating the hot lava below that continues to flow,
34:26carving out long underground tunnels.
34:32Living in a tube like this
34:34actually wouldn't be that crazy.
34:36In fact, this is a big tube.
34:38I mean, it's quite large, but, you know,
34:40the ones on the moon are ten times bigger than this.
34:42On the moon,
34:44lava tubes run beneath hundreds of metres of solid rock,
34:47protecting the tunnels from radiation,
34:50micrometeorites,
34:52and keeping the temperature stable.
34:57A lava tube like this on the moon
34:59would be nice and stable,
35:01and perhaps never get much colder
35:03than the coldest caves on Earth.
35:12Astronauts on the moon
35:14could seal themselves inside tubes like this
35:17by adding airlocks.
35:20If we were able to colonize a lava tube
35:22under the lunar surface,
35:24we could actually adjust the environment.
35:26We could pump in air, we could make the temperature right.
35:28You could actually get out and walk around
35:30in this vast subterranean tunnel.
35:34You could have an entire city down there
35:36lighting up the walls of the lunar terrain.
35:38A lava tube would be a great first lunar station.
35:40I mean, it's like a ready-made home for us.
35:43In the future,
35:45when we have colonies on the moon,
35:47they may very well be inside of these lava tubes.
35:49It'll be dark all the time.
35:51You're in a cavern.
35:53It'll have to be lit,
35:55but you don't have to worry about
35:57enclosing your domes or anything like that.
35:59It's already a sealed, self-sufficient environment.
36:01You fill it with air,
36:03and you can live in it outside.
36:05It'd be pretty amazing.
36:07You don't have to worry about sixth gravity.
36:09You don't necessarily need a space suit.
36:11That would be fantastic.
36:13Now, if you want to go out on the surface,
36:15which you would have to eventually,
36:17yeah, you have to wear a space suit,
36:19and yeah, you've got to be able to
36:21protect yourself and all that.
36:23But I think living in one of these colonies
36:25would be really astonishing.
36:27You could fly.
36:29You could have wings.
36:31You could make wings and flap and fly.
36:33There have been science fiction novels written about this.
36:35I would love to see this someday.
36:37Some of these lunar space stations
36:39could be self-sufficient.
36:41There are craters that are always shaded,
36:44and they contain water ice.
36:46And so that is really exciting
36:48because we didn't realize
36:50that there was actually still water on the moon.
36:53We thought the moon was just bone dry for many years.
36:56That was the mantra.
36:58And now we're finding out that contained in soil,
37:00contained inside of crater walls
37:02that are permanently shadowed,
37:04there is lots and lots of water ice.
37:07Water is the perfect resource
37:09for a lunar launch pad.
37:11As well as drinking it,
37:13you can split water with electricity
37:15to create oxygen to breathe
37:18and hydrogen to use as a fuel.
37:21When you think about it,
37:23rocket fuel is made of liquid hydrogen
37:25and liquid oxygen.
37:27And hey, those are the components of water.
37:29The moon's craters
37:31hold around 6 billion tons of water ice.
37:34That's enough to launch
37:3520 rockets into space every day
37:38for over 100 years.
37:46For over 4 billion years,
37:48the moon has driven our evolution,
37:50shaped our climate.
37:53And in the future,
37:55its resources will allow us to conquer space.
37:59But it's not going to be around forever.
38:05Sometimes when we talk about things that are reliable,
38:08we say there's nothing as reliable
38:10as the rising of the sun, right?
38:12We can think of the moon in the same way.
38:14It goes through its phases.
38:16It's there night after night, year after year.
38:18But it turns out
38:20the moon is actually moving away from the earth.
38:22And that's due to the interaction
38:24of the moon and the earth's tidal bulge.
38:27The bulge of water pulled up by gravity
38:30sits slightly ahead of the moon
38:32because the earth spins faster than the moon orbits.
38:35The moon pulls by gravity on that bulge
38:39and slows the earth's rotation.
38:41Over billions of years,
38:43that has slowed the earth's rotation a lot.
38:45We used to be spinning a lot more rapidly,
38:47probably more than twice as fast as we do now.
38:50The moon's attraction to the bulge
38:53has the opposite effect on its own orbit,
38:55speeding it up.
38:58This increased speed
39:00makes the moon's orbit wider
39:02pushing it further and further away.
39:06It's a very small amount.
39:09So it's only about 3.8 centimeters,
39:11which is about an inch and a half a year.
39:14Over billions of years,
39:16the moon will shrink to a dot in the night sky.
39:20And the earth's spin will become so slow
39:23that the moon will appear to freeze above our heads.
39:27There will come a time
39:29where the earth is actually locked.
39:30One side of the earth faces one side of the moon
39:32and the two of them will go around in lockstep.
39:37So there'll be one place on earth
39:39where you can see the moon.
39:41So you might imagine you'd have to go on
39:43some kind of vacation
39:45to actually see the moon at that point in time.
39:47But that's going to be a long time from now.
39:49So, you know,
39:51I wouldn't start booking your tickets quite yet.
39:55Is this the long-term future of our moon?
39:59Some scientists envision a more dramatic ending.
40:03A death by fire that will destroy the moon
40:06and, quite possibly, all life on earth, too.
40:10The process begins with the expansion of the sun.
40:14The actual future history of the earth, moon system,
40:17will depend upon the sun.
40:19And it could produce remarkable effects.
40:23As the sun gets older, it expands,
40:25filling the inner solar system with a dense solar wind.
40:30This wind will impede the moon.
40:34So as the moon orbits around the earth,
40:36there'll be drag.
40:38There'll just be more stuff in space
40:40for the moon to push against.
40:42So the moon has been moving away from the earth
40:44for billions of years.
40:46Maybe at that point it'll start coming back.
40:48This new inward trajectory is a death spiral.
40:53The moon eventually is going to spiral closer and closer.
40:58And then, because of the gravitational forces,
41:00the tidal forces are going to be so strong,
41:02it's going to essentially explode.
41:0418,000 kilometers above the surface of the earth,
41:07the moon reaches a point of no return.
41:11The gravitational pull of the earth finally overwhelms it.
41:16And you'll see it shaking, you'll see it quaking.
41:19It'll be stretched way out.
41:20It'll be stretched sort of toward us and away from us.
41:22It'll be hard to tell.
41:24But eventually you'll see that actually breaking apart,
41:28an entire world being shattered by the gravity of earth.
41:36The fractured remains of the moon
41:38create a Saturn-like ring of rocky debris.
41:43Having a ring around the earth would be a phenomenal sight.
41:48I would love to see that.
41:50You would look up and you would be able to see the ring.
41:53It would be at an angle to the earth.
41:55If you were at the right place on the earth,
41:57you'd be able to see it broad, stretching across the sky.
42:00I don't know if you'd be able to see it during the day,
42:03but at night it would be one of the most spectacular sights I can imagine.
42:09But the beauty soon turns to terror,
42:12as pieces of the ring rain down on earth.
42:20I mean, it's going to be an awesome sight, a terrifying sight.
42:24I mean, the whole sky is going to be filled with raining meteors
42:29just showering through the sky and they're going to be huge.
42:40Eventually all of that material will be incorporated into the earth
42:44and now these two siblings, separated at birth,
42:47now are finally again one body.
42:51From the fiery inferno, a new earth is born.
42:57But this world is sterile.
43:01The moon's presence allowed life to arise on the earth
43:05and the moon's presence will also destroy life on earth.
43:09The moon giveth and the moon taketh away,
43:12so that's kind of a neat storyline, although maybe not so great for us.
43:20It's pretty sad to imagine the earth without the moon.
43:23We're partners, we've affected each other's development.
43:29Seeing the moon in the sky is something that gives me joy every single time,
43:33that has never gotten old.
43:36We can't help but show affection towards it.
43:39It's there every night staring at us
43:42and of course romances have been written about it
43:45and will continue to be written about it.
43:47Life on earth may not have existed without the moon,
43:50but certainly without it, even if it did,
43:53it would be much less romantic.