Pluto may have liquid ocean under its icy crust, reveals NASA's New Horizons probe data

NASA’s New Horizons aircrafts has released a new analysis of data which suggests that Pluto may have a liquid ocean under its icy crust. Last year, New Horizons had unveiled that the dwarf planet might have or had one time a sub-surface liquid ocean. Scientists from Brown University in the US used a thermal evolution model for Pluto updated with data from New Horizons. They found that if Pluto’s ocean had frozen, it would have caused the entire planet to shrink.

Researchers however said that no signs of a global contraction were found on the surface of Pluto. On the contrary, New Horizons showed signs that Pluto has been expanding.

New Horizons beamed back pictures from its close encounter with the Kuiper Belt’s most famous denizen. It was then found that Pluto was much more than a simple snowball in space.

The exotic surface of Pluto is made of different types of ices – water, nitrogen and methane. There are hundreds of meters high mountains and a vast heart-shaped plain on Pluto.

It also has giant tectonic features - sinuous faults hundreds of kilometres long as deep as 4 kilometres. The tectonic features made scientists think 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,” said Noah Hammond, a graduate student in Brown University.

“A subsurface ocean that was slowly freezing over would cause this kind of expansion,” Hammond said. Scientists believe that there may have been enough heat-producing radioactive elements within Pluto’s rocky core. This could be a reason for the melting of the 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 an ocean that was frozen or in the process of freezing, extensional tectonics on the surface would result, and that is what New Horizons saw.

The thermal evolution model showed that because of the low temperatures and high pressure within Pluto, an ocean that had completely frozen over would quickly convert from the normal ice we all know to a different phase called ice II.

Ice II has a more compact crystalline structure than standard ice, so an ocean frozen to ice II would occupy a smaller volume and lead to a global contraction on Pluto, rather than an expansion.

“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,” she said.

The new model bolsters the case for an ocean environment in the furthest reaches of the solar system. The study was published in the journal Geophysical Research Letters. 

(With inputs from PTI)