New map reveals geology and history of Pluto’s moon Charon

Albedo-based map of Charon’s encounter hemisphere Albedo is a measure of the amount of light reflecting off a surface.
Credit: Robbins, et al., 2019

What a difference a planetary flyby makes. Pluto’s moon Charon—once no more than a fuzzy blob of pixels beside a larger blob—now has its first geological map, published in AGU’s Journal of Geophysical ResearchPlanets.

The new map was made with data and images collected by the 2015 flyby of the New Horizons spacecraft, which managed to gather enough data to map about a third of Charon’s surface.

In that area, the scientists have identified 16 different kinds of geological units, or areas with similar landscapes, along with 10-kilometer-tall cliffs; more than a thousand grooves and other long, linear features; and a patchwork of light and dark ground.

To get the elevations of the cliffs, troughs, craters and other features, the team used multiple images of Charon taken as the spacecraft flew past to create stereo 3-D images. These images are taken from different positions, so they can be processed using the same principle that our own brain uses to take images from two eyes and give us depth perception.

The new map shows possible evidence of a world that may have once split open like a chapped lip, or a rising cake, then released icy materials from its interior to flood over large areas – what are called cryoflows. In fact, the researchers have found that Charon has perhaps one of the most convincing examples of large cryoflows found in the solar system so far.

Crater Enigma

The new map has revealed many puzzling features of Charon, including its craters.

“Surprisingly we see very, very few degraded craters,” said Stuart Robbins of the Southwest Research Institute and lead author of the new paper. “On Mars we see old (degraded) and new craters. On Charon pretty much every  we see looks like it was created recently.” Either that or the craters they see have been around a long time without anything changing them, he added.

One explanation for the lack of aged-looking craters might be that some process erased the older craters. That process might be ancient icy flows – cryoflows – that welled up through cracks in the surface of Charon and buried the older craters.

If so, then perhaps sometime in Charon’s past its interior warmed up and underwent a chemical or physical change that caused it to expand slightly. That expansion cracked the surface – analogous to how the surface of a cake cracks as the cake rises while baking, Robbins explained. Then warmer materials from below oozed out over Charon’s surface. That material would have hidden a lot of Charon’s original surface, along with craters that were on that . This would also explain features that look like broken blocks of the moon’s crust caught and surrounded by a flood of fresher material.

Oz, Vulcan and Spock

To organize Charon’s features based on the cryoflows, the authors of the map described and named three major epochs in the history of Charon: Ozian, Vulcanian and Spockian.

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