by Bethany Augliere Wednesday, October 19, 2016
Last year, images from NASA’s New Horizons flyby of Pluto revealed geologic activity that suggested a liquid ocean may have once lurked beneath the dwarf planet’s icy crust. But whether it still exists in that state, or had frozen, remained a question. According to a new study published in Geophysical Research Letters, it may still be partially liquid.
Pluto orbits in a region of space called the Kuiper Belt, a swarm of icy bodies beyond Neptune. Originally, scientists believed that the dwarf planet would be similar to our own moon: inactive and covered in craters. Instead, deep winding surface fractures that stretch hundreds of kilometers cover Pluto’s surface, likely due to tectonic activity.
That tectonic activity is the result of global expansion, which is caused by a slowly freezing subsurface ocean, said Noah Hammond, the lead author and a graduate student from Brown University, in a statement.
But to determine if the ocean had already frozen, Hammond and his co-authors, including Edgar (Marc) Parmentier of Brown and Amy Barr Mlinar of the Planetary Science Institute based in Tucson, Ariz., developed an updated model incorporating key data — such as Pluto’s density and size — collected from the New Horizons probe. Based on the high pressure and low temperature conditions of the planet’s interior, the model suggested that a frozen ocean would convert the ice shell from regular ice to ice II, which is more compact. If that were the case, Pluto would have contracted rather than expanded.
“We don’t see the things on the surface we’d expect if there had been a global contraction,” Hammond said. “So we conclude that ice II has not formed, and therefore that the ocean hasn’t completely frozen.”
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