Cracks in Pluto's moon Charon indicate it had an underground ocean

This is a mosaic of images showing cracks in Saturn's moon Enceladus taken by the Cassini spacecraft during its close flyby on March 9 and July 14, 2005. 

Credit: NASA/JPL/Space Science Institute

If the icy surface of Pluto's giant moon Charon is cracked, analysis of the fractures could reveal if its interior was warm, perhaps warm enough to have maintained a subterranean ocean of liquid water, according to a new NASA-funded study.

Pluto is an extremely distant world, orbiting the sun more than 29 times farther than Earth.

With a surface temperature estimated to be about 380 degrees below zero Fahrenheit (around minus 229 degrees Celsius), the environment at Pluto is far too cold to allow liquid water on its surface. Pluto's moons are in the same frigid environment.

Pluto's remoteness and small size make it difficult to observe, but in July of 2015, NASA's New Horizons spacecraft will be the first to visit Pluto and Charon, and will provide the most detailed observations to date.

"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 in Greenbelt, Maryland.

"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."

is lead author of a paper on this research now available online in the journal Icarus.

This artist concept shows Pluto and some of its moons, as viewed from the surface of one of the moons. 

Pluto is the large disk at center. 

Charon is the smaller disk to the right. 

Credit: NASA, ESA and G. Bacon (STScI)

Some moons around the gas giant planets in the outer solar system have cracked surfaces with evidence for ocean interiors – Jupiter's moon Europa and Saturn's moon Enceladus are two examples.

As Europa and Enceladus move in their orbits, a gravitational tug-of-war between their respective parent planets and neighboring moons keeps their orbits from becoming circular.

Instead, these moons have eccentric (slightly oval-shaped) orbits, which raise daily tides that flex the interior and stress the surface.

It is thought that tidal heating has extended the lifetimes of subsurface oceans on Europa and Enceladus by keeping their interiors warm.

In Charon's case, this study finds that a past high eccentricity could have generated large tides, causing friction and surface fractures.

The moon is unusually massive compared to its planet, about one-eighth of Pluto's mass, a solar system record.

It is thought to have formed much closer to Pluto, after a giant impact ejected material off the planet's surface.

The material went into orbit around Pluto and coalesced under its own gravity to form Charon and several smaller moons.