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Pluto has left astronomers perplexed since the world was first discovered in 1930. And its mysteries grew only as a result of NASA's New Horizons spacecraft, which crossed the dwarf planet in 2015. A point of confusion is Sputnik's Planitia , part of the familiar heart-shaped region of the northern hemisphere of Pluto.
New Horizons instruments have suggested that there may be an underground ocean in the area. Otherwise, the tiny, far-off world would be so cold that it would have completely froze. However, Pluto's crust in the same region is finer in some areas than in others, and that makes sense only if it is frozen and hard, the melted snow would warm more evenly. Astronomers have been trying to explain these apparent contradictions since.
But now, a group of researchers think they have an answer. Scientists say that a thin layer of insulation – gases such as methane trapped in a layer of ice – could be the key to keeping Pluto both very cold and not quite frozen. The Japanese research team led by Shunichi Kamata released his findings Monday at Nature Geoscience.
A delicate balance
Scientists suspect that this insulating layer is made of a material called clathrate hydrate, which is a gas trapped in a solid layer like ice. On Earth, we think that frozen oceans produce more or less normal water ice. But on Pluto, oceans can contain large amounts of dissolved gases and other substances. If the oceans produce a frozen upper layer, this includes gases trapped in ice – and this substance will not act in the same way as normal ice.
Instead, this layer would have unique properties that fit into the strange puzzle of Pluto's oceanic and glacial layers. The layer is a good insulator – it does not exchange a lot of heat with the materials around it. And it's viscous, which promotes the slow movement of ice that leads to the strange thickness differences observed by scientists at Sputnik Planitia.
There are a few options for determining what type of gas might be hidden inside this insulating layer. But methane is one of the most likely suspects, because Pluto and many organizations like this have a lot of them.
Kamata and his colleagues came to their conclusions using detailed modeling and matching what their computer simulations predicted to what New Horizons has already revealed about Pluto. And Pluto is not the only cold world suspected of having underground oceans. Thus, while New Horizons has long since passed Pluto, scientists could still look for opportunities to observe this insulating layer in more detail.
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