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  • [♪ Intro ]

  • Remember ʻOumuamua?

  • It was the interstellar asteroid astronomers spotted last fall, and it got everyone all

  • psyched because it's an interstellar asteroid.

  • It came from outside our solar system!

  • If we want to study a different part of the galaxy we can't do that because we can't

  • get there but sometimes there comes here!

  • But, that object was just passing through, though, so scientists didn't have a ton

  • of time to study it.

  • But this week, according to a paper published Monday in MNRAS: Letters, there's some good

  • news: We seem to have found another interstellar asteroid.

  • Except, instead of just visiting our solar system, this one permanently moved in.

  • The object is named 2015 BZ509, orBee-Zedfor short, and it orbits the Sun in a pretty

  • wonky orbit.

  • For one, it moves backwards, or retrograde.

  • It circles the Sun clockwise, instead of the counter-clockwise motion we see in all of

  • the rest of the solar system.

  • Its orbit is also pretty elliptical, and it's inclined 163° below the ecliptic, which means

  • it's at a really strange tilt.

  • Astronomers first spotted this asteroid in 2015 -- like the name suggests -- but they

  • originally thought it was just part of a class of objects called Centaurs.

  • These are objects, both asteroids and other icy bodies, that hang out between Jupiter and Neptune.

  • For the most part, scientists believe these objeccts originally came from the Kuiper Belt

  • or the Oort Cloud -- two regions past Neptune -- but got pushed in among the planets by

  • gravitational encounters with other objects.

  • Because of all that, their orbits are pretty chaotic!

  • Like, that's actually the technical term: They are in chaotic orbits, with all kinds

  • of tilts, shapes, and directions.

  • Still, Bee-Zed was always especially weird among the Centaurs.

  • And this new paper has a hypothesis about why: It's not from around these parts.

  • The team ran statistical simulations on lots of objects like this asteroid, tracking their

  • possible orbits over the entire life of the solar system.

  • And they found that Bee-Zed specifically has an unusual, but really stable orbit.

  • In fact, it appears that it didn't get nudged toward the Sun like other Centaurs: It's

  • been hanging around there since the time when the planets formed around 4.5 billion years ago.

  • But if it's been around for that long, its orbit should be a lot more normal.

  • It should've formed from the same spinning disk of matter as everything else.

  • And that would mean it would have a similar orbit to everything else.

  • The researchers suggest that Bee-Zed could only have such a strange path if it came from

  • outside the solar system, and was later captured by the Sun's gravity.

  • Basically, billions of years ago, it immigrated to our neighborhood.

  • Based on those simulations, it probably wasn't the only one, either.

  • There may be a bunch of other extrasolar asteroids orbiting on even weirder paths.

  • The simulations showed lots of potential objects congregating on an orbit perpendicular to

  • the solar system, which the researchers dubbed the polar corridor.

  • If it's realin more than just the mathit would start a long way away from the Sun.

  • So if these other objects exist, they'd be orbiting really far out there, even into

  • the Oort cloud around 150 million kilometers away.

  • And that would help explain why we haven't detected them yet: They'd be really hard to see!

  • Now, even though this paper made a good case, there's still a chance that Bee-Zed came

  • from somewhere closer to home.

  • There's still a lot we don't know about the regions beyond Neptune, and this simulation

  • also didn't show the asteroid being directly captured by the Sun or anything.

  • So it's still not a closed case.

  • But it is a good start and hopefully we'll figure out that it definitely is and then

  • we'll go visit it and it will be like visiting another part of the galaxy without having

  • to have, like, lightspeed drives.

  • Meanwhile, in this week's more local news, scientists may have figured out why Saturn

  • has such weirdly shaped moons.

  • The planet has at least 62 of them, and lots of the smaller, inner ones have just some

  • wild shapes.

  • Like, there's Pan, which is shaped kinda like a little empanada, and Atlas, which looks

  • like a ravioli.

  • And then there's Prometheus, which looks vaguely like a burrito.

  • I haven't had lunch yet.

  • We've wondered for a while why these tiny moons are shaped the ways they are, and thanks

  • to a paper published Monday in Nature Astronomy, we think we know!

  • Based on a combination of modeling processes, the authors suggest those moons got their

  • shapes from specific kinds of impacts between smaller objects called moonlets.

  • To get their results, they simulated a bunch of these moonlets using a mix of N-body simulations

  • and smooth particle hydrodynamic, or SPH, modeling.

  • N-body simulations describe the gravitational interactions of massive objects hanging out

  • together, and SPH modeling is great for impacts.

  • According to these processes, a few things could happen when the moonlets crashed into each other.

  • Depending on the angle they collided, they could either merge, stick together for a bit

  • and then separate, or glance off each other in, like, “hit-and-runs”.

  • In those cases, they didn't merge, and they also probably didn't exchange insurance information.

  • Most of Saturn's inner moons seem to have formed when the moonlets stuck together.

  • And their weird shapes were specifically determined by the angle at which they collided.

  • In the simulation, oblique collision angles gave more oblong, burrito-like shapes, creating

  • moons like Prometheus.

  • And more direct collision angles made an equatorial ridge, like on Pan and Atlas.

  • These models also apply to at least one of Saturn's larger, more distant moons, too:

  • Iapetus, which also has an equatorial ridge.

  • Of course, we'd figured for a while that collisions were involved somewhere in these

  • funny shapes, but that's also kind of just the astronomer's fall-back.

  • Weird shape?

  • Probably something ran into it.

  • Weird orbit?

  • Probably something ran into it.

  • Covered in lava?

  • Something ran into it.

  • You get the idea.

  • Now, we at least have some serious math to back up that hypothesis!

  • Well, at least for these moons, not for all the other weird stuff in space.

  • That will hopefully come later.

  • Thanks for watching this episode of SciShow Space News!

  • If you'd like to keep up to date with the latest news from the solar system and beyond,

  • please go to youtube.com/scishowspace to subscribe.

  • Please.

  • [♪ Outro ]

[♪ Intro ]

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木星の近くに星間小惑星が隠れている (There's an Interstellar Asteroid Hiding Near Jupiter)

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    林宜悉 に公開 2021 年 01 月 14 日
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