Pluto’s largest moon is Charon and, from the looks of a photo sent back by the New Horizons spacecraft, it’s getting even larger. The picture shows what appear to be stretch marks indicating that Charon might be eating too many meteors and bursting at the seams. Or was it once pregnant and gave birth to a big baby moon? What do scientists think?

The marks appear in an image taken by the Long-Range Reconnaissance Imager (LORRI) on July 14, 2015, when New Horizon was about 48,900 miles (78,700 km) from Charon. The ridges and valleys in the photo look like what one would expect to see if a planet or moon suddenly expanded and contracted. The largest of these marks is a chasm measuring over 1,100 miles (1,800 km) long and 4.5 miles (7.5 km) deep. This chasm, almost four times the length and depth of Earth’s Grand Canyon, is one of the largest on any body in the solar system.

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Close-up views of Charon's stretch marks

A chasm that big deserves a name and this one has been christened Serenity Chasma by NASA scientists who think they have an explanation for it. While we know that Charon is now covered with water ice, the cracks indicate that it may have once been warm enough that the ice was liquid water, most likely beneath the surface in large oceanic pools where heat was generated from radioactive decay or some other internal heat sources.

Ice works the same way everywhere in the solar system, so when the underground ocean froze, it expanded upwards, forming the pregnant bulge on the surface that created cracks, canyons, lines and other planetary stretch marks.

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The "other" Charon

While “stretch marks” seems (or should we say ‘seams’) like the best way to describe Charon’s condition, scientists up on their Greek mythology know that Charon is the ferryman of Hades who carries souls across the rivers Styx and Acheron and described the marks in more macho terms as:

… like Bruce Banner tearing his shirt as he becomes the Incredible Hulk - Charon’s surface fractured as it stretched.

Whatever the marks look like, they’re a mystery no more.

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Are you saying I'm mooning you?

Paul Seaburn
Paul Seaburn is the editor at Mysterious Universe and its most prolific writer. He’s written for TV shows such as "The Tonight Show", "Politically Incorrect" and an award-winning children’s program. He's been published in “The New York Times" and "Huffington Post” and has co-authored numerous collections of trivia, puzzles and humor. His “What in the World!” podcast is a fun look at the latest weird and paranormal news, strange sports stories and odd trivia. Paul likes to add a bit of humor to each MU post he crafts. After all, the mysterious doesn't always have to be serious.

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