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00:00From the drama of our planet's origins and the birth of our solar system comes
00:10one of the most startling revelations of modern science. The solar system we see
00:16today, quiet, stable, was once a battlefield.
00:23Newborn planets blasted through space, competing for stable, circularized orbits
00:31inside a grunge-style mosh pit of gas and dust. For those that find the right balance,
00:39the prize is survival. For the rest, world-shattering destruction. A new look at the
00:49chaos of creation, and a frightening possibility in our distant future.
00:56Mars.
01:12The Curiosity rover is searching for clues about the origins of the red planet.
01:21It confirms the presence of oxygen and nitrogen isotopes, hidden in the rocks and soil.
01:32We use isotopes to try to figure out the history of planets, partly because they are immune to
01:41many of the changes, the chemical changes that occur when you have things like collisions and so forth.
01:46isotopes, the relative abundances of these isotopes are like fingerprints.
01:53Curiosity confirms a unique mix of isotope fingerprints.
01:57The isotopes indicate that Mars formed elsewhere in the solar system and moved into our neighborhood.
02:04Our solar system is full of oddities pointing to an imperfect birth and a malformed evolution.
02:19All of our planets go around the sun in the same direction that the sun is spinning.
02:26This is the same direction that the clouds within our original nebula began to rotate.
02:33Six planets spin around their poles in the same direction.
02:39For them, the sun rises in the east and sets in the west.
02:47Yet two planets spin the opposite direction.
02:56For Venus and Uranus, the sun rises in the west and sets in the east.
03:06Uranus not only has a retrograde spin, it rolls on its side like a bowling ball.
03:13At Neptune, the icy moon Triton orbits backwards, opposite from the direction of Neptune's spin.
03:24Do these planets spin backwards because they were rocked by titanic collisions in the past?
03:32So we see evidence in the architecture of the solar system for not only collisions like Earth's moon
03:38and the fact that Venus is rotating in the wrong direction and Uranus is on its side.
03:43So for all these things are attributed to collisions.
03:45We also see in the asteroid belt and in the Kuiper belt, the outer asteroid belt if you like,
03:51we see that the orbits of these things look like they've been disturbed.
03:55Closer to home, our own Earth has an inexplicable 23 and a half degree tilt.
04:05Its spin axis is radically misaligned from its magnetic pole.
04:10And our moon is comparatively large for a planet our size.
04:16Now, a new theory may be able to explain many of these oddities.
04:27It is called the Grand Tack Hypothesis.
04:40From four and a half to five billion years ago, a gas giant planet arose inside a primordial disk of gas and dust.
04:53Jupiter didn't just form where it is, but formed and then moved inward towards the sun.
05:03As it spirals toward the sun, Jupiter herds asteroids and rubble.
05:09Jupiter's natural tendency is to drift in slowly through this debris field that it's traveling around.
05:30The inner solar system is also thick with gas and dust.
05:34The birth of our planetary system is well underway.
05:39Numerous worlds are born in this region, including the Earth.
05:45Primordial skies are ruled by chaos.
05:51Jupiter's approach destabilizes these planets.
05:57Their orbits decay into wildly swinging ellipses.
06:07Some are tossed out.
06:10Others fall into the sun.
06:14Their numbers are unknowable.
06:16These are ghost worlds from a bygone age.
06:20Jupiter just causes all heck to break out in the solar system.
06:27And all that debris in the outer solar system gets flung inward towards the inner solar system.
06:33And it was a busy time in the very early solar system.
06:37And things were colliding with each other all the time.
06:47And then, it stopped.
06:50Jupiter's invasion of the inner solar system is mysteriously halted.
07:02The planet makes a turn.
07:04Or, in sailors' parlance, a grand tack.
07:11Lurking behind Jupiter is a second gas giant.
07:15Saturn.
07:20So, as Jupiter was migrating inward, Saturn was following it and growing.
07:24And as Saturn was growing, it came to have a size that it had a gravitational impact on Jupiter,
07:31which became more important than the gravitational interaction between the gaseous disk and Jupiter.
07:41They reversed direction.
07:45And, in a sense, you can think of Saturn and Jupiter feeding off one another and moving back out.
07:52Gravity tugs each passing planet.
07:56This transfers orbital energy from one world to another.
08:01All you have to do is exert a very subtle, little, periodic force at the right time,
08:08and you can have amazing changes in the motion of the object you're pushing on.
08:13Once enough energy has been transferred, the planets synchronize their orbits.
08:19They are said to be in a resonance.
08:22For planets, resonances are achieved and maintained through the mutual push and pull of gravity,
08:28through the fabric of space.
08:30They're a key factor in the continuing evolution of our solar system.
08:35This effect can be duplicated in the lab.
08:40We have ten metronomes here, set up on a swinging platform.
08:46They have little weights on pendulums here, but they've all been set at the same frequency.
08:52And I'm going to try to start them as best I can, completely out of phase, randomly.
08:59So their oscillation is going to transfer energy by the swinging of this plastic sheet
09:06to the other metronomes that are out of phase to get into phase with the majority.
09:12It's inevitable that there is going to be some majority group which starts out swinging more or less together,
09:21and they are eventually going to win out.
09:24I'm just doing this as randomly as I can.
09:37Aha!
09:38Maybe in this corner I see four that are pretty closely synced.
09:43Yes, now it's more like five.
09:48Six.
09:49Now you have one that's almost completely out of phase.
09:54Every time the majority hits a beat, it's going to give a little impulse, a little push to the platform,
10:02and that push is transferred to the metronome that's not in sync.
10:11Because the platform, you can actually see this platform vibrating back and forth in sync with the majority of these metronomes.
10:18Working on this one.
10:24So we're pretty close to resonance right now.
10:27As the metronomes achieve resonance, it's important to notice how the platform shakes.
10:36Now, it doesn't have to just be the force that's being transmitted by the plastic platform.
10:42It could be a force at a great distance, for example, the force of gravity.
10:46Just these small, little, seemingly insignificant pushes building up over multiple cycles can have dramatic energy transfer.
10:56That is how planets do it.
10:59Like the metronomes, the two gas giants form a resonance.
11:05We don't know exactly how long that took.
11:08But we have some fiducial marks for timing in the solar system formation.
11:12And that means that the grand attack had to have occurred relatively quickly.
11:15Talking hundreds of thousands of years, perhaps, to a million years.
11:20The two planets retreat until they reach their current positions.
11:26The sequence of planets as we find them today is based on Jupiter and Saturn's orbits.
11:33The planets eventually achieve a sequencing that many students learn through a mnemonic, such as,
11:39of course.
11:40My very educated mother just served us nine pizzas.
11:46Was there a time when the mnemonic was scrambled?
11:50Seems very likely the answer is yes.
11:52Not to mention a lot of additional letters were probably in there as well.
11:56Jupiter's menace of the inner solar system is finally over.
12:03If Saturn had not formed at the right time in the sufficient size,
12:09Jupiter would have continued migrating in, throwing out objects, unfortunate objects in the inner solar system,
12:15and ending up very close to the sun where it would stay.
12:19Yes, the Earth would be gone.
12:22Or the Earth would have had a terrifying encounter with Jupiter
12:27and would have had its orbit change dramatically to gosh knows what.
12:33There is mounting evidence that Earth had a terrifying visitor.
12:38Not Jupiter, but another world.
12:42Theia.
12:45Theia was essentially another proto-Earth where there were a number of these objects flying around.
12:51And Theia took time to grow just like the Earth did.
12:53They probably had rather similar histories.
12:56And for one reason or another, the orbit of Theia was perturbed such that it collided with the Earth.
13:02Theia was this planetary body that was roughly the size of Mars.
13:09And through this collision, a lot of particles were ejected, probably completely destroyed.
13:16We don't really know how much of Theia was preserved.
13:21Earth is rocked off its axis, its surface liquefied.
13:34Chunks of Earth's mantle are shoved into space.
13:41As a planetary body, Theia ceases to exist.
13:46Its remains are absorbed by the Earth and intermingled with the debris field.
13:53A new planetary body is formed.
13:56The moon.
13:58Further evidence is found in rock samples from the Apollo moon landings.
14:11This is a sample from the moon, if you can see it.
14:25This was collected by the Apollo 15 mission.
14:28Moon rocks contain isotopes identical to those found on Earth.
14:34When the moon arose, it is first covered with a magma ocean.
14:44People imagine the lunar magma ocean to be like this magmatic chamber I am describing,
14:50but at the surface and covering a whole planet.
14:56I see it as this ocean, like the Pacific, but this has to be like completely magmatic,
15:03orange and like probably like fluxing around and probably moving.
15:09Conditions in the lunar magma are as hellish as we can imagine.
15:15But a microscopic treasure forms in the magma.
15:19Crystal zircons.
15:22These are the same gemstones used in jewelry.
15:25But the zircons in the Apollo moon rocks yield a different treasure.
15:30So those zircons are very important because we know they crystallize in this lunar magma ocean.
15:36We know roughly when they crystallize in the lunar magma ocean.
15:39So they are one of these old pieces of the moon that we are looking for,
15:43one of these old pieces that we can use to date the origin of the moon.
15:49Zircons not only give the age of the moon, they set a specific date for the collision.
15:55The age of the moon is 4.51 billion years old.
16:024.51 billion years ago, Theia becomes part of Earth and forms the moon.
16:10But the story is not over.
16:13Space probes measure the moon slipping 3.8 centimeters further away each year.
16:20One day, the moon will break free.
16:25When that day comes, there will be no more tides.
16:30No more romantic moonlit nights.
16:33Could planetary orbits be inherently unstable?
16:39Could the chaos of planetary migration return?
16:44Haute-Provence Observatory, France.
16:54It's here that a discovery from a far away star gives one of the biggest revelations about our own solar system.
17:03The story begins when Swiss astronomers Didier Coelho and Michel Mayor notice something unusual about a star 50 light-years away in the constellation of Pegasus.
17:16Everything about this star is ordinary.
17:19A main-sequence mid-life yellow dwarf, just like our sun.
17:24But with one strange difference.
17:27The star at Pegasus 51 is rocking back and forth.
17:32It's a weird anomaly astronomers have never seen before.
17:37They check their instruments.
17:40Everything is working, including their new spectrograph, a device that splits the starlight from Pegasus into rainbow colors.
17:49Hidden inside the colors are patterns of lines.
17:53By tracking the day-to-day movement of these lines, astronomers make a startling discovery.
18:02Pegasus 51 has a planet.
18:06But no one has ever seen a world like this.
18:10It's half the mass of Jupiter.
18:13Yet it's extremely close to its star.
18:17Nine times closer than Mercury is to the sun.
18:22The planet at 51 Pegasus must be inside the corona, broiling in temperatures over a million degrees Fahrenheit.
18:31Soon, another planet is found around another star.
18:36And then another.
18:38And another.
18:41Astronomers have now confirmed over 3,700 exoplanets beyond our solar system.
18:48Nearly all of them are Jupiter-class planets grazing their host star.
18:54They're a new, previously unknown type called Hot Jupiters.
18:59They're so numerous, Hot Jupiters challenge theories about the origins of planetary systems.
19:05It's very difficult to make a planet close to the star because there isn't enough mass to build a giant planet very close to the star.
19:13And there's gravitational frustrations for trying to build a planet very close to the star.
19:18Astronomy is shaken with a new revelation.
19:22Planets do not stay put where they're born.
19:26When they're big enough, they migrate.
19:29It's a process called planetary migration.
19:34And yet, our own solar system has no hot Jupiter.
19:44Astronomers realize that Jupiter in our solar system was once on the move as well.
19:51But its migration was halted by a resonance with Saturn.
19:58Pegasus 51 shows where a planet lands when its migration is not blocked.
20:04The strongest evidence for the grand tack hypothesis comes not from our solar system,
20:10but from exo-worlds charted around other stars.
20:14Planetary migration is a universal concept.
20:18We see evidence of it out there in extrasolar planets, other solar systems.
20:24There's no reason why planet migration shouldn't have operated in our own solar system.
20:38The New Horizons probe finds evidence for roving planets within our solar system.
20:43While charting ancient craters on Pluto and on the surfaces of its moons,
20:50the science team discovered many craters are the same age.
20:55This suggests that they were formed by a single event.
20:59Even way out here, tiny Pluto was smashed by a wandering planet.
21:05The Pluto catastrophe may be related to other planetary migrations in the outer solar system.
21:12It was noticed that the exact orbits of the giant planets, particularly the outer giant planets,
21:22the icy planets, Uranus and Neptune, can be explained by their migration outward.
21:28There's a point in time, about 3.8 billion years ago, where Uranus and Neptune trade.
21:34And it's because of some of these mean motion resonance interactions that we were talking about earlier.
21:40So this mean motion resonance involving Jupiter and Saturn and so forth just causes all heck to break out in the solar system.
21:47Uranus and Neptune, all of a sudden, in 3.8 billion years later, they literally swap places.
21:51And all that debris in the outer solar system gets flung inward towards the inner solar system.
22:00The disruption in the outer solar system causes a new wave of violence.
22:05Astronomers call this epic the late heavy bombardment.
22:10Much of the cratering we see on our Moon today is from this period.
22:26It may be possible that swapping orbits with Uranus is how Neptune got its Moon.
22:32Astronomers call this epic the late heavy bombardment.
22:42Today, the epic of planetary migration appears to be over.
22:47The solar system seems stable, but what does the future hold?
22:53Computer simulations reveal what may be the greatest threat to the solar system in over 4 billion years.
23:01It comes from a very special relationship between Jupiter and Mercury.
23:06Mercury's orbit is slowly perturbed, thanks to a subtle but constant gravitational nudge from Jupiter.
23:15A new resonance, like the one between Saturn and Jupiter, that saved the inner solar system,
23:21is forming between Jupiter and Mercury.
23:26In 2001, computer models for the solar system were run 2,500 times.
23:35They plug in the positions and the orbits of all the planets in the solar system in a computer,
23:40and they just let it run through time, through millions of years, hundreds of millions of years, billions of years,
23:47to find out whether or not these orbits are stable.
23:53Change the location of one planet, say Mercury, by one millimeter,
24:00and you find that that change will give completely different predictions
24:06about where everything is going to be millions of years in the future.
24:13To see how quickly and easily things can change, we have only to go back to our metronomes.
24:19All I have to do is stop this platform from moving so that it cannot swing freely.
24:25Now there's no way for the metronomes to influence each other.
24:32They're good metronomes, but they're not perfect.
24:35They can't be going at exactly the same frequency in the same phase,
24:39and they're just going to fall apart because they have no way of forcing the others to go to resonance.
24:46The same applies to planets.
24:49Any small change can disrupt their harmony or restore it.
24:54Now that the platform is free to swing again, it can, again, transfer energy
24:59and sync them up just like we saw the first time.
25:06Scientists want to understand the consequences of a destabilized planet Mercury.
25:12In one case, Mercury leaves the solar system.
25:18The loss of its gravitational pull disrupts the balance of both Venus and the Earth.
25:24Earth and Venus swap orbits.
25:30The superheated atmosphere of Venus cools.
25:35Massive rains pour onto the face of the desert planet.
25:41Oceans arise.
25:44The land cools.
25:46And the air thins.
25:47Even the remains of an ancient visitor begin to cool off.
25:57Venus becomes like Earth.
26:01But the reverse happens to the Earth.
26:05As Earth settles into Venus's orbit, temperatures rise.
26:10The air becomes unbreathable.
26:13Glaciers melt.
26:16Oceans boil.
26:18The sun looms larger in the sky, only to be obscured by a thickening cloud cover.
26:26Suffering will be great, but brief.
26:31The entire four-billion-year pageant of life is cooked in a matter of days.
26:40Complete and utter destruction and elimination of all life on Earth.
26:44I'm not just talking about higher life.
26:46I'm not just talking about civilization.
26:48But everything, a sterilization of the planet, is something that I would want to think about
26:55a bit.
26:57There is another possibility.
27:09Equally dark and apocalyptic.
27:14A runaway Mercury is deflected by the gravity of Venus.
27:19And barrels toward the Earth.
27:23It may be a frightening encore to the opening act of our solar system.
27:29The equilibrium of the ages is over.
27:37If this scenario is correct, Mercury crashes into the Earth.
27:42Just as Theia did four billion years ago.
27:49The question is, could it happen today?
27:56Or is it a fate far away in the future?
28:02At a time when mankind itself is but a distant memory?
28:08The problem is that even with a perfect computer that understands all of the laws of motion perfectly,
28:20not just gravity but all the other subtle forces that go into it,
28:24you cannot give it accurate enough initial information about the locations, the masses, the sizes,
28:31the speeds of all of the objects in the solar system.
28:35Odds are, we may never see such a calamity.
28:40And yet, among the billions of stars in our galaxy,
28:44how many worlds are on the move?
28:47How many will share this fate?
28:50Is it this fate?
28:51We will not share this fate.
29:14Transcription by CastingWords