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We may have found another interstellar asteroid and scientists have some new ideas about how Saturn's moons got their weird shapes.

Host: Hank Green

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Sources:
https://www.nasa.gov/feature/goddard/2018/new-study-shows-what-interstellar-visitor-oumuamua-can-teach-us
http://www.astro.uwo.ca/~wiegert/2015BZ509/
Carroll, Bradley W., and Dale A. Ostlie. “Minor Bodies of the Solar System” In An Introduction to Modern Astrophysics, 2nd ed. San Francisco: Pearson Addison-Wesley, 2007.
https://doi.org/10.1038/s41550-018-0471-7
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Images:
https://en.wikipedia.org/wiki/Centaur_(minor_planet)#/media/File:Kuiper_belt_plot_objects_of_outer_solar_system.png
http://www.spacetelescope.org/images/opo1447a/
https://www.nasa.gov/multimedia/imagegallery/image_feature_2065.html
https://www.nasa.gov/image-feature/jpl/pia21436/pan-revealed
https://www.nasa.gov/image-feature/jpl/pia17207/prometheus-up-close
https://www.nasa.gov/jpl/cassini/pia18324/ring-slicer
https://www.nasa.gov/image-feature/jpl/pia20499/where-the-small-moon-rules
https://apod.nasa.gov/apod/ap050201.html
[♪ 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, or “Bee-Zed” for 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 real — in more than just the math — it 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 ].