Subsurface ocean on Pluto likely still exists
According to a new analysis led by a Brown University Ph.D. student, such an ocean likely still exists today.
The study, which used a thermal evolution model for Pluto updated with data from New Horizons, found that if Pluto's ocean had frozen into oblivion millions or billions of years ago, it would have caused the entire planet to shrink.
But there are no signs of a global contraction to be found on Pluto's surface. On the contrary, New Horizons showed signs that Pluto has been expanding.
"Thanks to the incredible data returned by New Horizons, we were able to observe tectonic features on Pluto's surface, update our thermal evolution model with new data and infer that Pluto most likely has a subsurface ocean today," said Noah Hammond, a graduate student in Brown's Department of Earth, Environmental and Planetary Sciences, and the study's lead author.
The research, which Hammond coauthored with advisors Amy Barr of the Planetary Science Institute in Arizona and Brown University geologist Marc Parmentier, is in press in Geophysical Research Letters.
The pictures New Horizons sent back from its close encounter with the Kuiper Belt's most famous denizen showed that Pluto was much more than a simple snowball in space.
It has an exotic surface made from different types of ices - water, nitrogen and methane. It has mountains hundreds of meters high and a vast heart-shaped plain. It also has giant tectonic features - sinuous faults hundreds of kilometers long as deep as 4 kilometers. It was those tectonic features that got scientists thinking that a subsurface ocean was a real possibility for Pluto.
"What New Horizons showed was that there are extensional tectonic features, which indicate that Pluto underwent a period of global expansion," Hammond said. "A subsurface ocean that was slowly freezing over would cause this kind of expansion."
Scientists think that there may have been enough heat-producing radioactive elements within Pluto's rocky core to melt part of the planet's ice shell.
Over time in the frigid Kuiper belt, that melted portion would eventually start to refreeze. Ice is less dense than water, so when it freezes, it expands. If Pluto had on ocean that was frozen or in the process of freezing, extensional tectonics on the surface would result, and that's what New Horizons saw.
There aren't many other ways on Pluto to get such features. One way might have been through a gravitational tug of war with its moon, Charon.
But the active gravitational dynamics between the two have long since wound down, and some of the tectonics look fairly fresh (on a geologic timescale). So, many scientists believe that an ocean is the strongest scenario. ■
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