In 2015, the dwarf planet, Pluto, received its first visitor from Earth. NASA’s New Horizons probe sent back spectacular images that showed, among other things, the “heart” of Pluto – a region named Tombaugh Regio consisting of, among other things, the unusually light-colored Sputnik Planitia. This is a plain that is up to one to nine kilometers deep, covers approximately the surface area of Texas, and is coated with nitrogen ice.
From its existence, researchers could already assume a few things – among other things, there is probably a liquid ocean under Pluto’s surface, like the kind that also exists on the moons Enceladus and Europa. However, for Pluto, which orbits far into the outer reaches of the Solar System, it is hard to imagine that this ocean didn’t freeze solid a long time ago. For the oceans on moons, for example, it is assumed that the gravity of the giant planets that they are orbiting produces enough heat to keep them in a liquid state. Pluto doesn’t have a heating mechanism like that.