A thin layer of ice-trapped gas molecules at the base of Pluto’s ice shell may insulate the ocean beneath, suggests an article in Nature Geoscience. This layer could explain why Pluto’s subsurface ocean has not yet frozen, and why similar oceans persist on other icy planetary bodies.

Observations of Pluto by NASA’s New Horizons spacecraft in 2015 suggested the presence of an ocean beneath an ice shell of varying thickness. However, the temperature required to prevent the ocean from freezing is thought to be too high to maintain the variable thickness of the shell.

Shunichi Kamata and colleagues propose that a layer of gas hydrates - molecules of gas in a lattice of water ice molecules - at the base of the ice shell may insulate the ocean and shell from one another. The researchers calculated how Pluto’s temperature and ice shell thickness would have changed through time with this layer. They find that a thin layer of gas hydrates is sufficient to maintain both a subsurface ocean and thickness variations in the ice. They suggest that the gas in the hydrates is most likely methane, rather than nitrogen molecules that escape to supply Pluto’s atmosphere. This methane may be derived from the comet-like material that formed Pluto, chemical reactions in Pluto’s rocky core, or a combination of both.