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  • [♩INTRO]

  • It's been more than 20 years since astronomers discovered the first planet

  • orbiting a star beyond our own.

  • And today, there's a catalog of more than 3700 confirmed exoplanets,

  • along with thousands more unconfirmed candidates.

  • But now, we might have found the very first moon beyond our solar system,

  • or an exomoon.

  • Last week, Science Advances published the first quote-unquote

  • compelling evidenceof a huge,

  • Neptune-sized exomoon 8,000 light-years away.

  • In 2017, data from the Kepler Space Telescope seemed to contain hints that an

  • exomoon might be out there.

  • The data revealed that a body the size of a gas

  • giant was orbiting a larger body called Kepler-1625b.

  • Now, two astronomers from Columbia University have used the even-stronger

  • Hubble Space Telescope to further explore the system.

  • And from what they saw, it looks like that exomoon signature

  • isn't some error in the data.

  • In the new study, the team used the transit method to study 1625b.

  • In other words, they analyzed the light coming from its star and how it dims

  • as the planet passes between the star and us.

  • The weird thing was, about 3.5 hours after the planet's transit ended, there was

  • a smaller dip in brightness.

  • That suggests the planet has a moon trailing it.

  • To the disappointment of space nerds everywhere (including us) the team

  • ran out of observation time before the potential moon had finished its own transit.

  • So they don't have a full set of data to analyze.

  • The good news is, there is a little more data

  • that supports the planet having a natural satellite:

  • The planet's transit started over an hour earlier than was predicted.

  • That could happen if it had a moon tugging on it

  • and changing the system's center of gravity.

  • So far, all this evidence suggests this moon, if it exists,

  • is comparable in mass and size to Neptune.

  • By our standards, that's huge.

  • But since the planet is around the same size as Jupiter

  • and a few times more massive, it makes sense.

  • Then again, these properties aren't based on the strongest models,

  • so there's still some uncertainty.

  • It could be that our data is a bit off and that there isn't a moon at all.

  • Instead, there could be a second planet in the system that's responsible,

  • although there hasn't been any evidence of that so far.

  • It's also possible that 1625b could just have

  • a longer orbital period than we think.

  • Or it could be orbiting at such a distance or angle that it's not transiting every

  • time we look at it, which could be why our predictions were off this time.

  • Right now, the authors of this paper confess this first exomoon has to survive

  • years of scrutiny and follow-up before its existence can be confirmed.

  • But if it does end up being a moon beyond our solar system,

  • it will be a really important target to continue studying.

  • For example, since it's likely much, much larger than any moon in our system,

  • it opens the question of how planetary systems form and evolve.

  • And the moon's origins at the moment are a total mystery.

  • Like, was it captured, or did it form alongside its partner?

  • At this point, we can only guess.

  • In other moon news, a study published online this week in Nature Geoscience

  • predicts a decent chunk of Jupiter's moon Europa

  • might be covered in giant ice blades!

  • Officially, these blades are called penitentes.

  • They're formed when large chunks of frozen water heat up and sublimate,

  • turning directly from a solid into a gas.

  • On Earth, we see this happen in places like the top of the Andes Mountains.

  • But we've also seen evidence of these blades on Pluto.

  • For penitentes to form, the environment has to be super dry and cold,

  • the air has to be really still, and the sunlight has to hit the ice

  • at just the right angle and for long enough periods of time.

  • Then, the Sun's radiation causes heaps of water molecules to sublimate,

  • carving deep depressions into the surface and turning everything really spiky.

  • In other words, the penitentes don't grow up like stalagmites do

  • they're leftovers!

  • Eventually, penitentes smooth out or break apart,

  • either from geologic activity beneath the surface or space debris

  • smashing into them from above.

  • But the amount of time that takes can vary.

  • To learn more about Europa, astronomers wanted to determine the likelihood,

  • location, and size of penitentes.

  • So they created a model.

  • It took into account things like how Europa is tilted toward the Sun,

  • its range of temperatures, and the reflectivity of its surface.

  • They also needed to estimate how often space debris would crash into

  • Europa's surface, which would smooth out its features.

  • According to their model, water could sublimate faster than erosion could

  • smooth things out at latitudes below 23° or so.

  • That means, for a large band around Europa's equator,

  • we'd likely see a healthy population of penitentes.

  • The team also calculated that, over 50 million years

  • which is the average age of Europa's surface

  • the blades could get up to 15 meters tall.

  • That's three times taller than what we usually see on Earth.

  • Of course, all their stats are averages, and don't take into account local

  • geologic features, or exactly how impurities in the ice will play a role.

  • So there may be more to the story.

  • Unfortunately, our technology near Europa doesn't have the proper resolution

  • to find photographic evidence of this spiky surface.

  • But there is both ground-based radar and thermal data

  • from the 1990s Galileo probe that suggests penitentes could be there.

  • Studies like this are cool, but they're about more than just uncovering giant ice

  • spikes on a far-flung moon.

  • To scientists and engineers, this kind of information is really important

  • to know when planning a future lander mission to Europa.

  • The moon is one of a few that scientists are almost definitely sure has a liquid

  • water ocean beneath its surface.

  • And although there aren't any landers officially on the docket right now,

  • we'll need all the information we can get when we are ready to go.

  • Thanks for watching this episode of SciShow Space News!

  • And thanks especially to our Patrons on Patreon.

  • The things beyond our planet are beautiful and fascinating,

  • and we love getting to explore them with you.

  • [♩OUTRO]

[♩INTRO]

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初のエクソムーンを発見したかもしれない!| サイショウニュース (We May Have Found the First Exomoon! | SciShow News)

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    林宜悉 に公開 2021 年 01 月 14 日
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