According to Scientists from Brown University, Pluto may have a liquid ocean under its icy crust.
The scientists used a thermal evolution model for Pluto updated with data from New Horizons and found that if its ocean had frozen, it would have caused the entire planet to shrink.
However, the massive mountains and deep faults on the dwarf planet’s surface suggest that Pluto has been expanding, a fact consistent with an unfrozen subsurface ocean.
“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.
How could the water remain liquid if Pluto is so cold due to it’s distance from the sun? The slow natural decay of radioactive elements in Pluto’s core may have been sufficient to keep the water unfrozen beneath the icy surface.
The idea of a liquid water ocean on Pluto isn’t new. We now know that Pluto’s surface consists of nitrogen, methane, and CO2. It’s also widely accepted that these exotic ices are merely a dusting atop a much thicker, water-based mantle that extends all the way to a rocky core. Most of that mantle is probably frozen—but it’s possible that a layer hugging close to the hot core is still liquid.
“The formation of ice II would cause Pluto to experience volume contraction and compressional tectonic features to form on the surface,” Hammond explained. “Since the tectonic features on Pluto’s surface are all extensional and there is no obvious compressional features, it suggests that ice II has not formed and that therefore, Pluto’s subsurface ocean has likely survived to present day.”
This research has implications for the search for new planets. If a liquid ocean can exist so far from the Sun, watery planets could exist elsewhere in the universe, despite considerable distance from their stars.
“That’s amazing to me,” Hammond said. “The possibility that you could have vast liquid water ocean habitats so far from the sun on Pluto – and that the same could also be possible on other Kuiper belt objects as well – is absolutely incredible.”