[meteorite-list] Pluto's 'Hulk-like' Moon Charon: A Possible Ancient Ocean?

[Ron Baalke]

http://pluto.jhuapl.edu/News-Center/News-Article.php?page=20160218

Pluto's 'Hulk-like' Moon Charon: A Possible Ancient Ocean?
February 18, 2016

Pluto's largest moon may have gotten too big for its own skin.

Images from NASA's New Horizons mission suggest that Charon once had a 
subsurface ocean that has long since frozen and expanded, pushing out 
on the moon's surface and causing it to stretch and fracture on a massive 
scale.

The side of Charon viewed by the passing New Horizons spacecraft in July 
2015 is characterized by a system of "pull apart" tectonic faults, which 
are expressed as ridges, scarps and valleys - the latter sometimes reaching 
more than 4 miles (6.5 kilometers) deep. Charon's tectonic landscape shows 
that, somehow, the moon expanded in its past, and "like Bruce Banner tearing 
his shirt as he becomes the Incredible Hulk" - Charon's surface fractured 
as it stretched. 

Charon's outer layer is primarily water ice. When the moon was young this 
layer was warmed by the decay of radioactive elements, as well as Charon's 
own internal heat of formation. Scientists say Charon could have been 
warm enough to cause the water ice to melt deep down, creating a subsurface 
ocean. But as Charon cooled over time, this ocean would have frozen and 
expanded (as happens when water freezes), pushing the surface outward 
and producing the massive chasms we see today.  

This image focuses on a section of the feature informally named Serenity 
Chasma, part of a vast equatorial belt of chasms on Charon. In fact, this 
system of chasms is one of the longest seen anywhere in the solar system, 
running at least 1,100 miles (about 1,800 kilometers) long and reaching 
4.5 miles (7.5 kilometers) deep. By comparison, the Grand Canyon is 277 
miles (446 kilometers) long and just over a mile (1.6 kilometers) deep.

The lower portion of the image shows color-coded topography of the same 
scene. Measurements of the shape of this feature tell scientists that 
Charon’s water-ice layer may have been at least partially liquid in its 
early history, and has since refrozen.

This image was obtained by the Long-Range Reconnaissance Imager (LORRI) 
on New Horizons. North is up; illumination is from the top-left of the 
image. The image resolution is about 1,290 feet (394 meters) per pixel. 
The image measures 240 miles (386 kilometers) long and 110 miles (175 
kilometers) wide. It was obtained at a range of approximately 48,900 miles 
(78,700 kilometers) from Charon, about an hour and 40 minutes before New 
Horizons' closest approach to Charon on July 14, 2015.