Beloved dwarf planet Pluto, while not quite large enough to warrant a planetary title, is still catching the eye of scientists. Its largest moon, Charon, may have once harbored oceans of water under its surface.
Once significant for being the former planet's only moon, Charon lost that title when four other moons, albeit smaller, were discovered orbiting Pluto. Then Pluto lost its planethood and Charon lost its fame-for a time.
Now scientists predict the moon may have fractures, which NASA says could be evidence of ancient oceans once flowing under its cold surface, putting Charon back in the speculative spotlight. In 2015 NASA's New Horizons spacecraft will visit the Charon as the first spacecraft ever to do so, and detailed images and observations will tell us whether or not the moon is really cracked.
Europa and Enceladus, moons of Jupiter and Saturn, respectively, contain cracked fractures. Both moons have evidence of interior layers of water, which scientists want to explore further for evidence of life. Europa and Enceladus have eccentric (non-circular) orbits caused by the gravitational tugs between Jupiter and Saturn and their other moons. This eccentricity causes high daily tides that create friction in the moons' interiors, releasing heat and keeping the insides of the moons warm enough to sustain subsurface bodies of water. The high eccentricity is also the likely cause of the fractures, as the surface of each moon is placed under a lot of stress while its insides broil.
"Depending on exactly how Charon's orbit evolved, particularly if it went through a high-eccentricity phase, there may have been enough heat from tidal deformation to maintain liquid water beneath the surface of Charon for some time," says Alyssa Rhoden from the Goddard Space Flight Center, the lead author of the study published in Icarus. "...we found it wouldn't have taken much eccentricity (less than 0.01) to generate surface fractures like we are seeing on Europa."
If Charon does contain fractures, they were most likely formed early in the solar system's history. The moon itself was formed from a high-impact collision on Pluto that sent off bits of the dwarf planet into orbit as moons. The distance between Pluto and Charon would have, at first, been quite small, allowing the gravitational pull between the two bodies to cause high eccentricity. This would have led to friction under Charon's surface, high tides and an interior environment warm enough to sustain a subsurface ocean.
Now at a temperature of -380° Fahrenheit, any water Charon once may have harbored will be frozen. A circular orbit is now in place so Charon is not under the gravitational pressure to which it was once accustomed.
Still, this study gives New Horizons an outlined plan of what to look for when it makes its journey to Pluto and Charon, roughly 29 times farther from the sun than Earth. In a fly-by it will be able to answer the question of whether or not the moon has fractures. If it does, there is strong evidence for water that once existed under the surface, and possibly, life.
