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  • Pluto might once have seemed like the last place in the solar system to look for liquid

  • water,

  • given that its balmiest days peak around negative two hundred twenty-five degrees Celsius.

  • But ever since the New Horizons probe flew by it in two thousand fifteen,

  • scientists have been studying what they think is Pluto's underground ocean.

  • Seriously!

  • They think Pluto has an ocean!

  • This hypothesis is based on various surface features New Horizons observed four years

  • ago

  • but even as the evidence piled up, it still wasn't obvious how Pluto had hung on to

  • this liquid water for so long.

  • Now, though, researchers think they might have figured it out.

  • On Monday, in a paper published in Nature Geoscience,

  • they announced that a layer of gas locked in ice could be protecting Pluto's underground

  • water.

  • If they're right, this could help us understand how a liquid ocean exists inside the dwarf

  • planet

  • and how other icy bodies might be holding onto hidden oceans of their own.

  • After the New Horizons flyby, scientists started to find a bunch of signs that Pluto might

  • have an underground ocean

  • including how they saw light reflect off its surface.

  • Strangely, the light appeared to be bouncing off crystals of ice.

  • That was weird, because ice can only hold its pretty, snowflake-like structure down

  • to a certain temperature.

  • When it gets really cold, ice molecules get all amorphous.

  • Not only that, but radiation from space also destroys those crystals.

  • So, scientists had lots of reasons not to expect crystal ice on the surface of Pluto.

  • But there it was.

  • Eventually, they figured out that the crystals were likely coming from underground water

  • that was erupting to the surface.

  • That might seem far-fetched, but later evidence from other surface features backed up the

  • idea that Pluto's ocean was still liquid.

  • For instance, if it had frozen, Pluto's surface would have buckled in recognizable

  • ways.

  • But there was no trace of that in the images.

  • Using data from the New Horizons flyby, scientists ultimately hypothesized that Pluto's hidden

  • ocean lay under a shell of ice that varied in thickness.

  • But they couldn't figure out how a shell like this could exist at the same temperature

  • that would keep the ocean from freezing.

  • They modeled lots of different scenariosmaybe the ocean was insulated by a thick surface

  • layer,

  • or maybe it was full of molecules like ammonia that act like antifreeze.

  • There were lots of possibilities, but nothing quite added up and matched the actual features

  • they saw.

  • But now, in this new paper, a team of scientists has landed on a hypothesis that seems like

  • it might work.

  • They suspect that a layer of gas molecules trapped in water ice is acting as insulation

  • between the ocean and the outer shell.

  • A material like this, called a gas hydrate, forms when water molecules act like a cage

  • that captures gas molecules.

  • This can happen when liquid water begins to freeze under high pressures and other special

  • conditions.

  • If the water has a high concentration of dissolved gas, it can freeze into a gas hydrate instead

  • of normal ice.

  • At the border between Pluto's ocean and its heavy shell of ice, scientists think this

  • just may have happened.

  • They tested this hypothesis by modeling two different versions of Pluto over time.

  • One version had this gas hydrate layer, and it kept its ocean and uneven ice shell as

  • the dwarf planet evolved.

  • The other version had no gas hydrate layer, and the ocean froze over in just a few million

  • years.

  • That's because gas hydrates conduct much less heat than regular ice.

  • Models suggest that it would only take a thin layer of trapped gas

  • just several kilometers or soto preserve temperatures on either side that could explain

  • both the liquid ocean and the uneven shape of the icy shell.

  • If this is the case, it might explain how objects way out in the Kuiper Belt could support

  • oceans, even though they're billions of kilometers from the Sun.

  • Even though scientists will be analyzing data from Pluto for a long time, New Horizons has

  • moved on to new adventures!

  • Most notably, on the first day of two thousand nineteen, it whizzed past the icy body MU

  • sixty-nine.

  • It's the most distant world a spacecraft has ever visited, and last week,

  • NASA published the first results from this flyby in the journal Science.

  • Now, this isn't the first time the New Horizons team has shared information about MU sixty-nine:

  • In January, the icy rock made headlines for looking like a couple of weird hamburgers.

  • But this is the first peer-reviewed paper with the scientists' analyses.

  • In their study, researchers tried to get to the bottom of how this oddly-shaped body formed,

  • by analyzing its shape and geological features.

  • They think the two lobes formed separately and fell into orbit around each other.

  • Then, eventually, it seems those two rocks came together and gently ran into each other.

  • This little fender-bender created the stuck-together hamburger situation, which scientists call

  • a contact binary.

  • But it's not just its shape that makes MU sixty-nine intriguing.

  • For one, it has a bunch of small pits across its surface.

  • Some of the larger ones probably came from impacts, but there are also some chains of

  • smaller, similarly sized holes that scientists think formed differently.

  • They might have formed when frozen solids turned to gas, or when material collapsed

  • into spaces under the surface.

  • At this point, it's still a bit of a mystery, but it's one teams will keep looking into.

  • MU sixty-nine is also, in the words of NASA, “ultra-red.”

  • It's not quite as red as Mars, but the entire surface has a red hue.

  • That's not totally bizarre, because observations suggest that a lot of Kuiper Belt objects

  • are reddish, but we don't know exactly why.

  • Researchers think the color could come from molecules that break down from light and radiation

  • and then combine into heavier molecules that are reddish in color.

  • There are still a lot of open questions and hypotheses to test, but fortunately, there's

  • still more information to come,

  • since New Horizons will keep sending back data on MU sixty-nine until late summer twenty

  • twenty.

  • In the meantime, the spacecraft will also keep zooming through the Kuiper Belt, studying

  • other objects from a distance.

  • It may even get assigned another target.

  • Regardless, scientists expect that the more they learn about MU sixty-nine and Pluto,

  • the more they'll understand about how our solar system formed.

  • Because, in the end, studying weird rocks in space is never just about those rocks.

  • By exploring these frigid bodies billions of kilometers away, we can learn about things

  • like how our planets were born, or where the solar system can support water

  • lessons from the edge of the solar system that hit very close to home.

  • Thanks for watching this episode of SciShow Space News, which is produced by Complexly.

  • We produce over a dozen shows, including PBS's Origin of Everything.

  • Join Dr. Danielle Bainbridge as she explores under-told histories and cultural dialogues.

  • From the history of the laugh track to the history of racial passing, no concept is too

  • small or too complex for Danielle to tackle.

  • Check out the Season 2 playlist in the description below!

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冥王星に液体の水の海があるかも!?| 冥王星には液体の水の海があるかも? (Pluto Might Have a Liquid Water Ocean?! | SciShow News)

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    林宜悉 に公開 2021 年 01 月 14 日
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