When a NASA spacecraft arrives at the distant dwarf planet Pluto in 2015, scientists will aim its cameras at the planet's icy moon Charon, looking for evidence it may once had had a liquid ocean under its surface.
Orbiting the sun 29 times further than the Earth is from the sun, Pluto -- and its several moons -- are believed to be as cold as 380 degrees F below zero.
Despite that frigid character, it's not outside the bounds of possibility Charon once possessed a hidden ocean of liquid water, scientists say.
Several moons in the solar system, such as Saturn's Enceladus and Jupiter's Europa, are believed to have oceans beneath their frozen surfaces, kept liquid by tidal flexing as the moons orbit the giant planets.
Pluto and its moon Charon have become tidally locked, so even if the moon did once possess a liquid ocean it would be completely frozen now.
However, scientists say, if Charon was subjected to large tidal forces in its past -- which would stress the surface and flex the interior, creating heat that might have made a liquid ocean possible -- the evidence may still exist as a characteristic network of cracks on its surface ice, NASA researchers say.
"Our model predicts different fracture patterns on the surface of Charon depending on the thickness of its surface ice, the structure of the moon's interior and how easily it deforms, and how its orbit evolved," said Alyssa Rhoden of NASA's Goddard Space Flight Center.
That model will be compared to what NASA's New Horizons spacecraft sees when it reaches Pluto in July of next year.
"By comparing the actual New Horizons observations of Charon to the various predictions, we can see what fits best and discover if Charon could have had a subsurface ocean in its past, driven by high [orbital] eccentricity," said Rhoden, author of the paper describing the research published in the journal Icarus.
Europa and Enceladus both display the characteristic pattern of cracks considered evidence of oceans under their surfaces.
With liquid water considered a necessary requirement for all known life forms, those moons of Jupiter and Saturn have figured in the search for extraterrestrial life.
Any signs of an ocean once existing on Charon would add evidence to such possibilities on the solar system's various moons, the researchers said.
"We're going to Pluto and Pluto is fascinating, but Charon is also going to be fascinating," said Rhoden.
