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  • [ ♪ Intro ]

  • Last week, after a three-and-a-half-year road trip and a more than 6-month surveying project,

  • the Japanese spacecraft Hayabusa2 successfully shot an asteroid.

  • Yes, with a bullet.

  • But that wasn't to protect itself, or to save the Earth from Armageddon or anything.

  • It was to kick up a sample of the asteroid's surface in order to collect it and bring it back to earth.

  • It sounds like a straightforward way to learn what the rock is made of,

  • but when push came to shove things could have gone pretty poorly.

  • Hayabusa2 is a follow-up to humanity's first asteroid sample return mission, Hayabusa.

  • That spacecraft visited a stony asteroid called Itokawa in 2005,

  • and returned to Earth with a very small sample of dust in 2010.

  • For this mission, the target was Ryugu,

  • a primitive carbon-based asteroid with an orbit not too far from Earth's.

  • It has a different chemical composition than Itokawa,

  • and likely hasn't changed much since it formed at the beginning of the solar system.

  • So studying it and space potatoes like it can help us unlock our history.

  • Except, there's a lot we're still learning about these kinds of missions,

  • so Hayabusa2 didn't go exactly as planned.

  • For example, the sample collection was originally scheduled for last October,

  • but once we got to the asteroid, images revealed that its surface was way bumpier than anticipated.

  • So the team needed longer to find the best place to touch down.

  • And even when they figured that out, the touchdown itself wasn't all smooth sailing.

  • It actually happened around half an hour before mission control expected it to,

  • although the Japanese space agency didn't mention why.

  • That could have been a huge problem, especially since they instructed the spacecraft to approach

  • Ryugu faster than they had originally planned.

  • But the good news is, it didn't crash.

  • At 45 meters above the asteroid's surface, Hayabusa2 automatically paused its descent,

  • then reoriented itself for the remaining stage.

  • But that required moving one of its antennas and that it could no longer send readings to Earth.

  • Which meant that all we could do was sit and wait for a signal that the craft had started getting closer to Ryugu

  • to confirm that touchdown was happening.

  • The moving antenna was always part of the plan, but that didn't make it any less nerve-wracking.

  • Still, it all worked out!

  • After getting Hayabusa2 back in the right position for communications,

  • mission control could confirm that the command to fire its bullet had been completed.

  • We won't know exactly how big of a sample it collected until the spacecraft comes home,

  • but there's a good chance we got something.

  • Hayabusa2 is scheduled to leave Ryugu late this year,

  • but not before collecting at least one more sample.

  • This one will be from below the surface,

  • which will require the craft to make a small crater using explosives.

  • If all goes well, these samples will return to Earth in 2020 and will provide data for decades.

  • And this isn't the only sample return mission humanity is working on, either.

  • NASA's OSIRIS-REx mission will sample the asteroid Bennu in mid-2020.

  • And although it's still in development, NASA's CAESAR mission could arrive at a comet in 2029,

  • if the space agency decides to move forward with it.

  • So it's safe to say space potato sampling will likely be a little more common in the future.

  • And speaking of space potatoeshow do like that transition?

  • In 2013, astronomers accidentally discovered Neptune's 14th moon hiding in pictures that

  • the Hubble Space Telescope took last decade.

  • But since the moon is so far away and hard to study,

  • the first scientific analysis of it was only published last week in the journal Nature.

  • And that finally allowed the International Astronomical Union to give this thing a proper name.

  • Hello, Hippocamp!

  • It sounds pretty goofy, but the name comes from a half-horse, half-fish creature from Greek mythology.

  • And all of Neptune's small moons get named after mythological water creatures,

  • or figures associated with Neptune or Poseidon.

  • At only 34 kilometers across, Hippocamp is by far Neptune's smallest moon.

  • It's also super close to the next moon over, called Proteus.

  • It's less than 12,000 kilometers away, which actually raises some questions.

  • See, Hippocamp is also about a thousand times less massive than Proteus.

  • So according to the general rules of orbits and gravity,

  • Proteus should have either thrown Hippocamp out of Neptune's system, or merged with it.

  • Unless, that is, Hippocamp is a literal chip off the old potato.

  • Astronomers hypothesize that this moon may have formed several billion years ago,

  • when something like a comet struck Proteus and broke off a piece of it.

  • Or maybe the collision threw out a bunch of smaller pieces in the same general area,

  • and they collected back into a tiny new moon.

  • Either way, there are a couple pieces of evidence to support this collision idea.

  • For one, models suggest that Proteus has been slowly migrating away from Neptune over time,

  • and billions of years ago, it would have been roughly where Hippocamp is now.

  • Also, we've detected a huge impact crater on Proteus,

  • which is more than large enough to have come from a collision that would have made Hippocamp.

  • As always, scientists will need to keep investigating to say anything for sure.

  • But one thing is obvious: Hippocamp backs up our previous idea that the Neptunian system is chaotic.

  • It might look all peaceful from a distance, but the area around Neptune is kind of like

  • a giant orbiting traffic jam.

  • For example, we know that the planet captured its largest moon, Triton,

  • after making its first generation of satellites.

  • So when Triton rolled in, it disrupted everybody's orbit and caused all kinds of collisions.

  • We also know that activity from comets has obliterated a bunch of moons.

  • In fact, the team studying Hippocamp estimates that it has been broken apart and reformed

  • nine different times over the past 4 billion years.

  • So this new study helps reinforce what we've already suspected.

  • And as a bonus, the team studying Hippocamp

  • was able to release new data on the other six, small moons inside of Triton's orbit.

  • That included data on Naiad, Neptune's innermost moon,

  • which hasn't been seen since Voyager 2's flyby in 1989.

  • So in addition to sayinghito Hippocamp, these scientists are helping us better understand

  • the evolution of our outermost planetary system.

  • Between this group and the Hayabusa2 team,

  • it seems like everybody is learning about the solar system's evolution these days

  • and we're pretty excited about it.

  • Thanks for watching this episode of SciShow Space News!

  • Since we haven't sent a spacecraft to Neptune in about thirty years,

  • there's a lot we're still trying to understand about the planet.

  • And while the Hubble Space Telescope can clearly do a lot, it can't do everything.

  • If you'd like to learn what mysteries we could solve with a Neptune orbiter,

  • you can watch our video all about it.

  • [ ♪ Outro ]

[ ♪ Intro ]

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我們剛剛拍攝了一顆小行星......為了科學!| 宇宙新聞 (We Just Shot an Asteroid... for Science! | Space News)

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    林宜悉 發佈於 2021 年 01 月 14 日
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