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  • [dramatic music]

  • [explosions]

  • NARRATOR: Our solar system has weathered

  • over 4 billion years of planet-altering catastrophes.

  • In some cases, the effects are obvious,

  • like the craters of the late heavy bombardment

  • that still litter the moon.

  • In others, the evidence has long since disappeared.

  • NASA has recently compared images of Jupiter

  • from the Cassini and New Horizons missions

  • and made a stunning discovery.

  • Like Saturn, Jupiter also has rings, though much fainter.

  • But something has disrupted them.

  • If you look at the rings of Jupiter,

  • they actually have little corrugations,

  • little ripples in them.

  • And those ripples are formed when a portion of the ring

  • is tilted.

  • And then as it continues to spin and evolve over time,

  • those ripples wander out, propagate

  • out through the ring system.

  • If you unwind that system and work back out the ripples,

  • you can find out the point in time

  • when that ring plane had gotten tilted over.

  • That point when that ring got tilted

  • was right around July of 1994.

  • NARRATOR: July 1994 marks the date of the Shoemaker-Levy 9

  • impact event.

  • The scientific sleuths had made a key discovery.

  • As the cometary fragments struck Jupiter itself,

  • much smaller debris passed through its rings,

  • tilting and twisting them into the ripples

  • that we still see today.

  • In the case of a disrupted comet like Shoemaker-Levy 9,

  • you've got an entire pall of dust,

  • a large mass of material distributed

  • across the disk of the rings raining through that system.

  • And so rather than displacing only one or two ring particles,

  • you can do the entire cloud at once, tipping it on the side.

  • NARRATOR: Shoemaker-Levy 9 wasn't

  • the only comet to leave its calling card mark

  • on Jupiter in recent times.

  • In July 2009, another asteroid smashed into the gas giant

  • near its south pole.

  • [explosion]

  • But when it impacted Jupiter, it brought up a lot of material

  • from deep within the atmosphere and created a huge scar

  • on the surface of the planet that

  • was visible for many weeks.

  • The size of this black ash cloud was

  • perhaps the size of the Pacific Ocean on the Earth.

  • It was quite large.

  • NARRATOR: It's now estimated that an asteroid or comet hits

  • Jupiter every 10 to 15 years, which

  • is 5,000 times higher than the rate of impacts on Earth.

  • And the fact that we've seen several of these

  • suggests that it's happening all the time because there

  • are all the ones we don't see.

  • So there's a lot more impact activity on the outer gas

  • giants than we ever thought.

  • If Jupiter was not in our solar system,

  • the Earth would be essentially a sitting duck

  • for all the debris, the comets and the asteroids

  • that were falling in towards the sun,

  • creating vastly larger numbers of catastrophes

  • on Earth than we've experienced through our history.

  • [roaring]

  • NARRATOR: But as our solar system ages,

  • new threats will likely arise, and Earth itself

  • will face a cosmic day of reckoning that nothing,

  • not even Jupiter, can prevent.

  • In several billion years, many scientists

  • believe Jupiter, the largest planet,

  • and Mercury, the smallest, will face off in an orbital duel.

  • And an innocent bystander, Earth, just might find

  • itself in the line of fire.

  • MICHAEL MISCHNA: Right now, our solar system

  • is kind of a paradigm of clockwork regularity.

  • But it turns out that the planets do affect

  • each other gravitationally.

  • The planetary orbits are, over very long periods of time,

  • vibrating in and out and turning.

  • Jupiter and Mercury will begin to turn

  • their orbits at the same rate.

  • And if that happens, Mercury's orbit becomes

  • progressively more eccentric.

  • It becomes progressively more elongated until the point

  • where, at its far point from the sun,

  • it's actually crossing Venus's orbit.

  • If Mercury's orbit ever gets to the situation

  • where it's crossing Venus's orbit, then basically,

  • all hell can break loose.

  • NARRATOR: Scientists have calculated one of four

  • disastrous consequences.

  • Mercury might collide with the sun,

  • might be ejected from the solar system, might smash into Venus,

  • or, in a worst case scenario, Mercury might collide

  • with the Earth, blasting away our mantle and atmosphere

  • and sterilizing our planet.

  • [explosion]

  • Mercury is hardly the only threat we face

  • from within the solar system.

  • According to some scenarios, Mars also

  • faces orbital chaos in the future,

  • and it too may slam into Earth, repeating the disaster

  • that gave rise to the moon.

  • And it's not just planets.

  • Nearby stars periodically disrupt comets

  • in the Oort cloud, which could send them on a kamikaze mission

  • through the solar system and set off

  • a new late heavy bombardment.

  • And if, as most expect, the Andromeda Galaxy ultimately

  • collides with the Milky Way, the galactic pileup

  • could shatter our solar system's deceptive calm.

  • The ultimate planetary catastrophe, I think,

  • is still in our future.

[dramatic music]

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超級行星災難 (The Universe) (第六季) - 歷史 (ULTIMATE PLANETARY CATASTROPHE | The Universe (Season 6) | History)

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    林宜悉 發佈於 2021 年 01 月 14 日
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