Pluto's Moon Charon May Have Had Underground Ocean

Posted on June 14, 2014

Pluto and Charon artists concept

Pluto's large moon Charon may have once been home to a subterranean ocean. NASA's New Horizons spacecraft will visit Pluto and Charon in July 2015 and could provide data that enables astronomers to determine if there was once an underground ocean on the moon. Cracks on the icy surface of the moon could indicate that its surface was once warm enough to sustain a liquid underground ocean. Astronomers say any underground ocean would likely be frozen today on the frigid moon.

The artists concept above shows Pluto and some of its moons as viewed from the surface of one the moons. Pluto is the center object in the image and Charon is located to its right.

Alyssa Rhoden of NASA's Goddard Space Flight Center and lead author of a research paper published in Icarus, says in a statement, "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. 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 eccentricity."

Jupiter's moon Europa and Saturn's moon Enceladus have cracked surfaces with evidence for underground oceans. These moons have slightly oval-shaped orbits that flex the interior and stress the surface. The astronomers say a past high eccentric orbit with Charon could have generated large tides, causing friction and surface fractures.

Charon has one-eighth the mass of Pluto and is believed to have formed after a giant impact ejected material off Pluto's surface. Astronomers say that initially there would have been strong tides on both Pluto and Charon that caused their surface to bulge toward each other.

Rhoden says, "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. Using plausible interior structure models that include an ocean, we found it wouldn't have taken much eccentricity (less than 0.01) to generate surface fractures like we are seeing on Europa."

NASA's New Horizons site says the spacecraft's closest approach to Pluto will be at 7:49:59 a.m. EDT (11:49:59 UTC) on July 14, 2015.

NASA, ESA and G. Bacon (STScI)