An article about to be published in the journal “Geophysical Research Letters” boosts the theory of the existence of an underground ocean of liquid water on Pluto. An analysis of data collected by NASA’s New Horizons space probe during its July 14, 2015 flyby carried out by Noah Hammond, graduate student at Brown University, Providence, Rhode Island, USA, offers some clues to support this amazing possibility.

Evidence of the presence of underground oceans in the solar system are becoming increasingly common, particularly concerning Europa, one of the largest moons of Jupiter, and Enceladus, a moon of Saturn. In those cases the presence of giant planets provides the energy needed to heat the water with its gravitational effects that deform these moons. The idea that liquid water could be present in Pluto’s underground is much stranger and yet isn’t new.

In 2011, well before the New Horizons space probe reached Pluto, a research investigated this possibility, based on the hypothetical presence of a sufficient amount of radioactive materials. Their decay could at least in the past have generated enough energy to make water liquid underground. Recently, another research analyzed the possibility that Charon, the largest moon of Pluto, may have had an underground ocean in the past.

Noah Hammond tried to analyze the evidence of the presence of an underground ocean on Pluto in the past or even today. His study is based on a thermal evolution model updated with data collected by the New Horizons space probe. According to this model, if in the past there was liquid water underground that at some point froze, the whole planet would have shrunk.

The shrinking would be due to the fact that the ice present on Pluto isn’t like the normal one we know on Earth, which has a volume larger than liquid water. At the temperatures typical on the dwarf planet and at the pressures existing in its underground ice would have a more compact crystal structure with a lower volume.

One of the clues suggested by the 2011 research concerned the presence of faults with cracks in Pluto’s surface. Those tectonic elements were found and there are also very large ones. This suggests the possibility that there is an underground ocean that is slowly freezing and consequently the water is turning into normal ice, expanding.

As for Charon, the hypothesis that there’s an ocean of liquid water in Pluto’s subsurface is based on clues far from enough to set the issue one way or another. To be clear, there’s much more evidence of the presence of underground oceans on Europa and Enceladus. However, the fact that this is a hypothesis seriously considered in various research shows that in recent years we’re considering possibilities that a few decades ago seemed absurd.