Professor Brian Cox explores the Solar System’s hidden realms, between and beyond the planets, where countless worlds lie shrouded in darkness.
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LearningTranscript
00:00There's something out there in the darkness.
00:20A world with no name.
00:22Its surface is ancient, and probably pink.
00:34We don't know where it came from, or how long it's been there, but we do know it's not alone.
00:44It's a dwarf planet, only discovered in 2018.
00:57Now you might reasonably ask, how could thousands of astronomers, both amateur and professional,
01:02miss a world that is pink and 400 kilometres across?
01:07Well, the answer might lie in its nickname, which is far, far out, because it really is far, far out.
01:20You might have thought of the solar system as the sun, and then all the planets lined up all the way out to Pluto.
01:26But we now know that that's just the tip of the iceberg.
01:30This is a journey to the least explored regions of our solar system.
01:44As we probe the mysteries of the asteroid belt.
01:52Visit frozen worlds that we're discovering beyond Pluto.
01:56And reveal a vast hidden kingdom, that even our most powerful telescopes can't see.
02:06Lost.
02:09In the dark.
02:26It was the sound that most people noticed.
02:52A sonic boom in the night.
02:56Travelling at almost 50,000 kilometres per hour, a rock tore through the atmosphere.
03:17Broke apart.
03:20And rained down across Winchcombe.
03:26A visitor from a distant realm.
03:46On the 28th of February 2021, a rock from space landed there, on this driveway.
03:53And it shattered into hundreds of pieces.
03:56Most of it went onto the lawn.
03:57Bits of it went onto the neighbour's driveway.
04:00And the indentation in the driveway that was here is now in the Natural History Museum.
04:06And here is a piece of that rock.
04:10And you see that it's very dark.
04:14It's almost black.
04:15Very different to the rocks that you find naturally around here.
04:19So the question is, other than the rather non-specific, it came from space, what exactly is this?
04:27And where exactly did it come from?
04:29The cows weren't the only ones watching that night.
04:41Doorbell and CCTV cameras never sleep.
04:44The network of specialist meteor cameras also captured it.
04:57And that meant it was possible to calculate its trajectory.
05:01Back over the skies of England.
05:11Out of Earth's atmosphere.
05:19Past Mars.
05:26And into the darkness.
05:27In between Mars and Jupiter.
05:35Lies a realm of rocky worlds.
05:39This is where that rock came from.
05:45The asteroid belt.
05:50Asteroids are rubble left over from the formation of the solar system.
05:54The remnants of planets that never were.
06:00It's thought that there are at least a million out here.
06:04So dark, they're incredibly difficult to see.
06:10But asteroids don't always stay in the asteroid belt.
06:14Every now and then, two asteroids collide.
06:26Causing fragments, big and small, to be lost from the belt.
06:30This can create havoc for neighbouring planets.
06:50Including...
06:51Our own.
07:04We've flown several spacecraft straight through the asteroid belt.
07:07But only one has stayed to explore the region itself.
07:21Most asteroids are like misshapen boulders.
07:23But one stands out from the rest.
07:33Much bigger than the others.
07:36And almost perfectly spherical.
07:42Dawn's target world.
07:44At first, Ceres appears dark and heavily cratered, like its fellow asteroids.
07:57But Dawn has discovered that it's different.
08:02Its surface is peppered with bright white crystals.
08:11So what are they?
08:14Now there is another world in the solar system where white crystals form on the surface.
08:29It's here.
08:30It's Earth.
08:32This is a mountain composed almost entirely of salt.
08:35It's mainly sodium chloride actually, table salt.
08:38There's a bit of magnesium and potassium in there which gives it those pinky colours.
08:43This is enormous.
08:44It extends hundreds of metres down into the ground.
08:48Now it formed because around 40 million years ago or so, this was the Atlantic Ocean.
08:54And then as a climate change, the oceans receded, evaporated away and left the salt behind.
09:00And then plate tectonics raised the ground up to form salt mountains.
09:07Now salt crystals like this only form in the presence of liquid water.
09:21Now salt crystals like this only form in the presence of liquid water.
09:35In this case, it was the Atlantic Ocean.
09:42That raises an intriguing question.
09:45Are those crystal deposits on the surface of Surrey salt?
09:49And if so, does that imply there was once an ocean on Ceres?
10:01Dawn entered into a close orbit.
10:03And by measuring sunlight reflected off the crystal deposits, it could determine what they're made of.
10:20Sodium carbonate.
10:23A common type of salt.
10:27A tantalising sign that Ceres had an ocean in its past.
10:31Orbiting just 35 kilometres from the surface, Dawn found another clue that suggests an ocean may still be there today.
10:50It detected a different type of salt crystal that's only been found in one other place in the solar system.
11:04When salt water evaporates, then it leaves these things behind, salt crystals.
11:18Essentially sodium and chlorine ions bonded together into a crystal lattice.
11:24But under the right conditions, when it's very cold, then a different sort of crystal can form when seawater freezes.
11:32It's called a hydrohalide.
11:34Essentially, water molecules are incorporated into the crystal lattice.
11:39Now we see hydrohalides here on Earth.
11:42But the fact that we also see them on Ceres presents a mystery.
11:47Because hydrohalides are unstable in a vacuum.
11:50It's been calculated they should only last around 100 years on the surface of Ceres before the water escapes out into space.
11:59So the fact that we find them implies that they must be constantly forming.
12:06And that in turn must imply that below the surface of Ceres, there is a reservoir of salt water today.
12:15Ceres is a world of water.
12:24It's thought salty subterranean lakes 40 kilometres deep exist beneath the surface today.
12:31But how did the salt end up on the surface?
12:39The answer lies in Ceres' location.
12:47Incoming asteroids can punch straight through to the lakes below.
12:51Exposed to the vacuum of space, the water vaporises instantly.
13:04Leaving its cargo of salt behind.
13:07And peppering Ceres with bright white spots.
13:18The discovery of water beneath the surface means this asteroid is now a candidate in the search for life.
13:26The more we've explored the asteroid belt, the more we've come to realise that it's not just a band of rubble.
13:41The dark worlds hiding here are worthy of exploration in their own right.
13:46And the asteroids that leave the belt can transform the planets nearby.
14:04Mars orbits closer to the asteroid belt than any other planet.
14:07And around 100 fresh impact sites appear on Mars every year.
14:26NASA's rovers have found some spectacular meteorites scattered across its surface.
14:37And one even spotted what looks like an asteroid in the sky.
14:53Floating in front of the sun.
15:03But it's actually one of Mars's two moons.
15:07The end of Mars...
15:11I mean, I think the developers have found some really good...
15:12and they think it's really good.
15:15I think there's a lot of people about the orbit.
15:15I think that we've gone through the ocean.
15:17I think we've got some color very nice.
15:17I know I have a number of people about the sun.
15:18Many of you are going to see the sun is in the sky.
15:21I have a number of people...
15:21...on the sky with our glass.
15:25I'm not going to see the sun is in this world.
15:27The sun is in the sky with our waters.
15:30Who knows the sun is in this world?
15:35We've got a number of people about the sea.
15:36And it's been called over the sun.
15:37Phobos isn't spherical like our moon.
15:40It's kind of a strange, irregular shape.
15:44So there's a theory, a simple theory.
15:47Maybe Phobos is an asteroid that came in from the asteroid belt
15:51and was captured by Mars's gravity.
15:54Well, actually, wonderfully,
15:56it turns out things aren't that simple.
15:59The European Space Agency has a probe in orbit,
16:07busily surveying the red planet.
16:13Mars Express orbits Mars three times every day,
16:18regularly passing beneath Phobos.
16:24Its high-resolution cameras captured the most detailed images
16:28of the moon ever seen.
16:36Showing a surface covered in strange grooves.
16:44Phobos looks like someone's ridden a bike all over it.
16:51But perhaps more intriguing,
16:53with the measurements Mars Express made of the tiny moon's mass.
16:58It's pretty hard, actually, to measure the mass of a small moon.
17:06But the way it was done was to measure how the path
17:09of the Mars Express spacecraft was deflected
17:12by the weak pull of Phobos's gravity.
17:15Now, once you have the mass,
17:17and we have a reasonable idea of the volume,
17:19we calculate the density.
17:21And that came as a surprise,
17:23because it turned out that Phobos
17:26is more like a kind of a gravel pile weakly held together.
17:31It's not very dense at all.
17:33And that does support the theory
17:35that maybe Phobos was formed from the debris
17:38of some kind of collision.
17:47So it's possible that Phobos is not a captured asteroid after all.
17:52But was in fact formed after a massive asteroid hit Mars.
18:03But there's still something about Phobos that neither theory can explain.
18:09Its strange grooves.
18:11This landscape was sculpted by the elements,
18:17by the wind and the rain.
18:19But on Phobos there is no wind and rain.
18:21And so the landscape is sculpted by something else.
18:24It's actually sculpted by gravity.
18:27When you've got a planet and a moon orbiting around each other
18:31and spinning on their axes,
18:33very complex gravitational forces come into play.
18:36They're called tidal forces.
18:38And they act to deform the moon
18:42and also actually slightly deform the planet.
18:45And they also act to change the orbits.
18:48And in the case of Mars and Phobos,
18:55what's changing is that Phobos is descending towards Mars in its orbit.
19:02And it's only about 6,000 kilometres above the surface now.
19:07But ultimately, over time, Phobos gets closer to Mars
19:11and that means the tidal forces get stronger and stronger.
19:18The grooves on the surface are stretch marks and fractures.
19:30Mars's gravity is tearing Phobos apart.
19:38Eventually, Phobos will drift so close
19:41that Mars's gravity will destroy it.
19:48But from this destruction, something beautiful will emerge.
20:07As Phobos begins to break apart,
20:09most of the debris will fall to the surface of Mars.
20:15But the rest will remain in close orbit,
20:20spreading out to encircle the entire planet,
20:26leaving Mars with a spectacular set of rings.
20:33So what is Phobos?
20:47The truth is, and I think this is wonderful,
20:50we still don't know the full story of the origin of Phobos.
20:54But what we can say is that this little moon is a wonderful place.
21:03Because in the future, it's going to turn the red planet into a ringed world.
21:10Leaving the asteroid belt behind, we travel out, further into the darkness.
21:29Beyond Jupiter, the gaps between the planets get ever wider.
21:36And the temperature plummets.
21:37Beyond Jupiter, the gaps between the planets get ever wider.
21:51We push on through millions of kilometres of empty space.
22:10Until we reach the furthest planet from the Sun.
22:23Neptune is wrapped in a dense blue blanket.
22:40Clouds of methane and ammonia thousands of kilometres thick,
22:46beneath which there is no detectable surface.
22:50But there are worlds out here that you could stand on.
22:57Neptune has at least 16 moons.
23:00And one of them is very unusual.
23:15Triton's surface is coated with pale nitrogen ice.
23:19But unlike the other moons, which are frozen to the core,
23:24Triton is an active world.
23:31Geyser-like plumes of gas and dust eight kilometres high
23:35stretch into Triton's upper atmosphere,
23:38which flattens them abruptly at 90 degrees.
23:42Creating a vista so strange.
23:45It's hard to believe it's real.
23:49How did a moon four and a half billion kilometres from the Sun become so active?
24:04In the 10th century, monks built a chapel on this hillside.
24:16It's an astonishing achievement.
24:17They carried all the stones up by hand.
24:21And when they'd finished, a solitary monk, a hermit, lived here contemplating the great mysteries of existence.
24:29And every morning, he would have seen the sun rise in the east.
24:32But now we know the reason for that.
24:34It's because the Earth's spinning on its axis.
24:38And in fact, everything spins in the solar system, and almost everything spins in the same direction.
24:51Now, it's a fundamental property of nature, that once things are spinning, they continue to spin, and continue to spin in the same direction, unless something happens.
25:14Triton doesn't spin in the same direction as almost everything else.
25:24It goes in the opposite direction in its orbit around Neptune.
25:28So there must be a reason for that.
25:44Triton's unusual orbit, which takes it around Neptune in the opposite direction to the inner moons, suggests that Triton didn't form alongside Neptune.
26:01It came from somewhere else.
26:04It's not true.
26:13Sometimes in science, things are quite simple.
26:16There are sort of rules of thumb that apply and are useful, and one of them, in the solar system, is that planets and moons that form in the same region around the sun, at the same distance from the star, are made of the same stuff.
26:32So, for example, here's Neptune, which is mainly made of hydrogen, helium, a bit of methane.
26:39And there is Uranus, which is made of hydrogen, helium and a bit of methane,
26:43because they formed in the same icy region far from the sun.
26:48Here's Mars, formed much closer in, and it's silicates and iron oxides, aluminium, magnesium, things like that.
26:56And there's the Earth, roughly the same place, same stuff again.
27:02Here is Pluto, made of water ice, nitrogen ices, methane ices, carbon monoxide.
27:10And here is Triton, same.
27:15So, we have a hypothesis, which is a guess, I suppose, that we could test.
27:22The hypothesis is that maybe Triton and Pluto formed in the same place.
27:32To understand Triton, we have to look deeper into the darkness.
27:40Neptune might be the furthest planet from the sun, but it's not the edge of the solar system, not even close.
27:51over a billion kilometres further out lies Pluto.
27:57And it's not alone.
28:00There are hundreds of thousands of other worlds out here.
28:04This is the Kuiper Belt, a vast frozen realm billions of kilometers wide.
28:21It's home to an exotic collection of icy worlds, including some 200 dwarf planets.
28:32Some have rings and moons, others are bizarre and misshapen, but they all share one thing
28:43in common.
28:45They're made of similar material to Triton.
28:49It seems then that the Kuiper Belt is where Triton belongs.
28:56So how did it end up in orbit around Neptune?
29:08The answer might lie in this strange geography of the Kuiper Belt itself.
29:13In one region, everything orbits the Sun, pretty much circular orbits like almost everybody
29:19else in the solar system.
29:21But there's another region where things orbit in ellipses.
29:25It's almost as if something flourished really the Kuiper Belt and disturbed it.
29:36There is one prime suspect.
29:41Neptune.
29:43It's thought Neptune formed much closer to the Sun, then slowly drifted out.
29:55Its gravity disrupted the Kuiper Belt and scattered the icy worlds.
30:03But Triton was unable to escape.
30:09To this day, Triton is trapped in a backwards orbit around Neptune.
30:16And being this close to a giant has consequences.
30:25Just as our Moon raises tides on the Earth, Neptune raises tides on Triton, stretching and
30:33squashing it, heating up its rock and ice.
30:43It's thought that this is what melts its frozen interior and powers the spectacular plumes.
31:02So here is the wonderful hypothesis of what might have happened to explain what we see on Triton.
31:17So as Neptune plowed through the Kuiper Belt in the ensuing gravitational chaos, Triton got
31:23captured into its preferred orbit.
31:25And even to this day, that orbit is ejecting energy into the Moon, where the tide is raised
31:32upon it by Neptune's gravity.
31:34And that's driving the geology.
31:36And I mean, isn't that a wonderful example of how you build a hypothesis in science?
31:41You put together the clues.
31:43So we have the composition of Triton, the same as Pluto.
31:47We have the strange geography of the Kuiper Belt, and we know that gas giants can change
31:53their orbit.
31:54Put those together, and we have a hypothesis of why Triton is the strange magical twilight
32:02world that we see today.
32:16Leaving Triton behind, we travel into the Kuiper Belt.
32:23We know very little about the worlds out here.
32:29They're so far away, we can't make them out in much detail.
32:36But we have sent one spacecraft to explore this region.
32:50It took over nine years for the New Horizons to get here and hone in on its primary target.
32:57The spacecraft captured the first close-up images of a Kuiper Belt world ever seen.
33:17It's such a spectacularly sunny güzel schön.
33:23We talk about 30 minutes before.
33:40Another world, hanging uncomfortably close in the sky.
33:57Charon doesn't rise or set,
34:00and it's only visible from one side of Pluto.
34:10Understanding why these two are so close together
34:16reveals something unique about this dark and distant realm.
34:26When Charon was first discovered in 1978,
34:29we just assumed it was a moon, Pluto's moon.
34:33But the more we've learned about Charon,
34:35and crucially, the more we've learned about the Pluto-Charon system,
34:39the more we've come to realise that there's more to it.
34:45All large moons in the solar system, including our own,
34:49have something in common.
34:52They only show one face to their parent planet.
34:58And the fact that all moons do this is not a coincidence.
35:02It's to do with the complexity of orbits.
35:06So let's say this is the Earth and I'm the moon,
35:08and we tend to think of the moon just orbiting around the Earth
35:11and the Earth sitting still.
35:12That's not what happens.
35:14Actually, both moon and Earth orbit around what's called
35:18the common centre of mass of the Earth-Moon system.
35:21It's just that because the Earth is way more massive than the moon,
35:24the centre of mass is actually inside the Earth.
35:27So the Earth is kind of doing that.
35:34Let me show you what I mean.
35:36So here's the Earth spinning on its axis once every 24 hours.
35:45That's one day.
35:46And there is the moon orbiting around the Earth
35:49once every 27 and a bit days.
35:54The gravitational interactions between Earth and moon
35:58cause their orbits to synchronise.
36:00The moon rotates on its axis exactly once
36:12for each lap it makes around the Earth.
36:16With the result that the same face of the moon
36:20always points to the Earth.
36:25But in the case of Pluto and Charon,
36:27the centre of mass of the system is outside of both bodies.
36:32And so they both orbit around the centre of mass,
36:35which is somewhere in space.
36:36That's where I'm standing.
36:38Now Pluto orbits once every six and a half Earth days or so
36:43and spins on its axis once every six and a half days or so.
36:48And Charon also orbits once every six and a half days or so
36:52and spins on its axis once every six and a half days or so.
36:56And the result of all that is that Charon always presents
37:01the same face to Pluto.
37:05And Pluto always presents the same face to Charon.
37:14Both worlds face each other in a synchronous dance.
37:18Now this might seem really strange and unusual.
37:24It isn't.
37:25It's a consequence of all those forces acting.
37:28This is what would happen to our Earth and moon given enough time.
37:31But enough time would be many times the current age of the universe.
37:35The difference here is that this is not a moon orbiting around a planet.
37:41It really should be thought of as two objects of similar mass orbiting around each other.
37:56Pluto and Charon are a double planetary system.
37:59Also known as a binary pair.
38:04Just 20,000 kilometres apart, they gaze at each other without ever turning away.
38:12This is the first double planetary system we've observed.
38:16But we think there could be many more.
38:22New Horizons is still out there today.
38:25Searching for more Kuiper Belt worlds.
38:30So far, it's encountered just one.
38:33Arrokoth is formed from another pair.
38:41Now so close, they're touching.
38:49So why do the worlds out here in the Kuiper Belt form these rare partnerships?
38:54The further from the Sun planets are, the slower they move.
39:05And way out here, they move very slowly indeed.
39:11But occasionally, collisions do occur.
39:18It's thought that in the past, Pluto and Charon crossed paths.
39:22But their glacial movement meant that this was less of an impact and more of an embrace.
39:36Instead of destruction, the pair became partners for life.
39:41Now we've only actually visited three worlds in the Kuiper Belt.
39:55Pluto, Charon and Arrokoth.
39:57But we have seen more using the Hubble Space Telescope.
40:01And what's interesting is that when we zoom in on those, what look like single pixels of light,
40:05many of them aren't single pixels.
40:08They're binaries, just like Pluto and Charon.
40:11So this is a pair of worlds called Typhon and Echidna.
40:14And it's a binary.
40:16And this is another pair of worlds, Banth and Orcas.
40:21And again, you can see them orbiting around each other, orbiting around their common centre of mass.
40:26And this complex gravitational dance, far from the Sun, means that the Kuiper Belt has a very complex structure that we don't really understand.
40:37So the Kuiper Belt does, in a very real sense, represent the frontier of our knowledge about the solar system.
40:45Almost.
40:46Past the Kuiper Belt, we enter a realm of true darkness.
40:55All we see are the bright stars of the Milky Way.
41:00Even our most powerful telescopes struggle to see anything in the solar system out here.
41:06But every now and then, things do show up in the darkness.
41:26In 2018, a faint point of light was detected.
41:29Ten billion kilometres beyond the Kuiper Belt.
41:43It's a dwarf planet.
41:48Nicknamed Far, Far Out.
41:52But we think there's more out there.
41:54A lot more.
41:57There's another realm of our solar system, far beyond the reaches of any spacecraft or telescope we've ever built.
42:11So vast.
42:13So strange.
42:15And so deep into the darkness.
42:16It's almost impossible to imagine.
42:30Imagine that pinnacle is the Sun.
42:33And I'm standing somewhere around the orbit of Neptune.
42:36And let's head out to the Kuiper Belt.
42:39Now, Neptune is about 30 metres away from the Sun.
42:42So on our scale, that means that the Earth would be one metre away.
42:47One metre.
42:49That's called one astronomical unit.
42:51The distance of the Earth from the Sun.
42:53It's about 150 million kilometres.
42:56So now I'm inside the Kuiper Belt.
42:59Traversing through that realm of icy worlds.
43:02And I reach Pluto.
43:04The furthest extent of its orbit, at the edge of the Kuiper Belt.
43:0750 astronomical units.
43:09So 50 metres away.
43:10And then, to the most distant object we can see.
43:14Well, we have to get a move on.
43:18Because it's a long way away.
43:20It is, of course, far, far out.
43:24That is the most distant object we have ever seen.
43:29And it is, well, 130 astronomical units away.
43:35130 metres.
43:36But remarkably, we strongly believe that there's another region, another realm to the solar system.
43:47But to go to the edge of that, we have to go far, far, far away.
43:52A wave.
43:53A wave.
43:54A wave.
43:55A wave.
43:56A wave.
43:57A wave.
43:58B
44:19Oh, my God.
44:49Oh, my God.
45:19Oh, my God.
45:49Two kilometres away from the sun, that's 2,000 astronomical units, and this is where
45:56we think another realm begins.
45:59And astonishingly to me, we think it extends 100 kilometres further.
46:06100,000 astronomical units, that's over a light year.
46:10Just imagine how many strange worlds that contains.
46:16This distant realm is known as the Oort Cloud, a mighty kingdom, at least a trillion strong.
46:30Hidden in the dark.
46:37Most are thought to be icy objects, the size of mountains.
46:41But it's likely some are made of rock.
46:47And if we were able to go there and visit them, we'd discover that they are pristine.
46:52Barely changed since the dawn of the solar system.
47:00Stretching out into interstellar space, and held in place by the sun's gravity,
47:13the Oort Cloud is our solar system's largest and most mysterious realm.
47:19But here's the thing, no telescope has ever seen anything in the Oort Cloud.
47:28And the most distant spacecraft from Earth, Voyager 1, is all the way back there.
47:33It's just beyond, far, far out.
47:36It's travelling at around a million miles a day.
47:40And it will take 300 years to get here.
47:44And 30,000 years to cross the Oort Cloud.
47:49But science doesn't deal in fairy stories.
47:52It's not as if somebody just said, well, that would be a good idea, let's invent it.
47:56So why are we so sure that it's there?
48:03For as long as we've been looking into the night sky,
48:09there have been signs that the Oort Cloud is real.
48:16And this is one of them.
48:25It's existed for billions of years.
48:27And for most of that time, it's been locked in a deep, frozen slumber.
48:40But now, it stirs.
48:47As it nears the sun, warm rays bathe its surface.
48:57And it begins to thaw.
49:27So much material is torn from the surface.
49:33It stretches out to form a tail.
49:4020 million kilometres long.
49:45It's a comet.
49:52Comet Nishimura was visible from Earth for just a few weeks.
49:55And it's by no means the first of its kind.
50:05Hale-bop.
50:10And Neowise lit up our skies for weeks on end.
50:14And when we followed their trajectories back,
50:24we discovered that they all came from the same place.
50:30300 billion kilometres from the sun.
50:33Countless comets throughout recent history
50:41have orbits that started in the Oort Cloud.
50:46And that's doubly surprising
50:47because comets have a very short lifetime.
50:51Many of them only last a few orbits around the sun.
50:54So that implies that there must be a vast reservoir of comets out here.
51:01And that is a central piece of evidence for the existence of the Oort Cloud.
51:06What does the Oort Cloud look like?
51:13Well, here's a fascinating thing.
51:15The comets all come from different directions.
51:18From over there and over there and down and across.
51:21From everywhere.
51:23Now, if the Oort Cloud was flat, like the Kuiper delts,
51:27we'd expect them to come from similar directions.
51:30Which implies that the Oort Cloud is not a flat disk,
51:37but some kind of giant sphere surrounding the sun.
51:45Now, just imagine the scale of the Oort Cloud.
51:49A giant sphere enveloping the entire solar system,
51:54stretching more than a light year every direction.
52:00We tend to think of the solar system as the sun,
52:09and all the planets and moons.
52:20But as technology's improved, we've discovered more.
52:26And more.
52:30Our exploration of the solar system has only just begun.
52:35We know that we've only explored the tip of the iceberg,
52:44the fraction of what's out there.
52:46Most of the solar system lies, at least for now, way beyond our reach.
52:51But by just making some observations of a few comets and asteroids,
52:57and even captured moons that have ventured inwards from the outer solar system,
53:00and by doing science, we've been able to build a picture
53:05and tell a story of our solar system.
53:09And we've discovered that it isn't just a few planets orbiting close to a lonely star.
53:15It is a vast structure that stretches outwards,
53:20maybe halfway to the nearest star.
53:23There's a real mystery surrounding Phobos,
53:51which is we don't really know what it is.
53:53It looks exactly like an asteroid,
53:56but it orbits Mars in a very circular orbit around its equator,
54:02which is not what you would expect.
54:05Phobos looks like an asteroid,
54:07but it behaves like a moon.
54:09So which one is it?
54:10We may soon have an answer.
54:16The Japanese Space Agency is planning an audacious mission to Phobos in 2026.
54:23The MMX mission, the Martian moons exploration mission,
54:29aims at going to Mars moon and bringing some samples of Phobos back to the Earth.
54:35I'm really confident that as soon as we have a sample of it on Earth,
54:41we'll know almost straight away what Phobos is.
54:45But landing on Mars' tiny moon with its low gravity,
54:50drilling into its surface and getting the samples all the way back to Earth
54:55in a single round trip is no mean feat.
54:59People have wanted to explore the Martian moons for a long time,
55:07have tried to send missions there,
55:08but they've failed for a number of reasons.
55:17Unfortunately, Phobos 1 didn't work on its way to the Mars system.
55:22And then Phobos 2 got there and sent back a little bit of data
55:28and then was lost contact with.
55:31In 2011, the Russian space agency Roscosmos made a third attempt.
55:43Phobos 2's probe blasted off from Baikonur Cosmodrome,
55:47but the Russian spacecraft failed to fire its own engines
55:51to set it on its path to Mars.
55:54When a mission fails, it's devastating.
55:57It's disappointing.
56:00But we've got to learn from mistakes.
56:02We need those failures to help us develop our instrument,
56:07to develop our mission in order to make it a success.
56:10If all goes to plan,
56:14the Japanese mission will transform
56:16our understanding of what Phobos is,
56:20giving new insights into how the moons and planets
56:23of our solar system formed.
56:26The MMX spacecraft is amazingly capable.
56:30It's got cameras and spectrometers
56:32and a rover and two sampling mechanisms.
56:35But it's also doing something that's never been done before,
56:39which makes it hard.
56:40And so to be ready for that,
56:44you have to put things through a whole array of tests.
56:47They'll vibrate everything the way it will when it launches.
56:51They'll put it through hot and cold temperatures
56:53like you'll experience from direct sun
56:55or from being in the cold of space.
57:00If the mission succeeds,
57:02the returned spacecraft is due home
57:04with its samples in 2031.
57:07When the sample gets back to Earth,
57:12we'll analyze it in our laboratories
57:13to find out what it's made of
57:15and therefore what Phobos is.
57:18Understanding the origin of Mars-Moon Phobos
57:22will help us to take a step forward
57:26to understand the evolution and the formation of our solar system.
57:31Next time,
57:40our solar system's most violent worlds.
57:44Where we encounter 20-kilometer-tall whirlwinds.
57:49Lightning 10 times more powerful than that on our planet.
57:52And slow-motion rainstorms
57:56on a distant moon.
57:59These are the storm worlds.
58:02We'll see you next time.
58:03We'll see you next time.
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