We had no idea what Pluto looked like until 2015 when the New Horizons spacecraft completed its flyby. It’s safe at this point to say that the former planet is a much more complex object than anyone dared expect. It has clouds, fields of nitrogen ice, and (surprisingly) a liquid water ocean. Scientists from the US and Japan think they’ve teased out the secrets of Pluto’s hidden water reservoir.
The idea of a liquid water ocean on Pluto came about in 2016 as scientists analyzed data gathered during the brief New Horizons flyby. Models of Sputnik Planitia, the left-hand lobe of Pluto’s “heart” suggested there was a liquid subsurface ocean driving the convection and remodeling of the surface. Pluto is, of course, frigid. The average surface temperature is a mere -380 degrees Fahrenheit (-229 degrees Celsius). That’s just 44 Kelvin from absolute zero.
So, how can there be liquid water all the way out there? Pluto doesn’t have volcanic activity, and it lacks a large companion whose gravity could cause tidal heating. According to the new analysis, the water ocean under pluto’s frosty crust could be insulated by pockets of gas like methane under the ice. These “clathrate hydrate” pockets of gas slow the transfer of heat from the planet’s interior via water. This hypothesis also pulls double duty as an explanation for the relative lack of methane in Pluto’s atmosphere.
The fascinating thing about this idea is that it could mean there’s a lot more liquid water in the solar system. Pluto is just one Kuiper Belt object, and the same process could be sustaining long-lived liquid oceans on other icy planetoids and moons in the solar system. That could mean many more planets and planet-like objects are potentially habitable.
Unfortunately, testing this hypothesis will prove challenging. New Horizons is long gone from Pluto — it only did a flyby because it was moving so fast. It’s on course to study more objects in the Kuiper Belt. To have any hope of nailing down the composition of Pluto, we need a probe that remains in orbit, or better yet a lander. No follow up missions to Pluto are in active development, but a 2017 NASA concept called for the development of a fusion drive, which is still far from reality. That should give you an idea how far off in the future we’re talking.