Weird and Active Pluto and Charon

The New Horizons spacecraft successfully completed its flyby of Pluto on Tuesday and collected all the scientific data it was planned to without a hitch. On Wednesday, we got our first pick at what these new data revealed.

Methane Ice

False-color image showing the chemicals on Pluto's surface. Credit: NASA.

False-color image showing the chemicals on Pluto’s surface. Credit: NASA.

This is an earlier false-color photo from before the flyby showing where the methane is. The “heart”, now Tombaugh Regio, is on the left, just rotating into view. This chemical signature shows that the yellowish region at the north pole and the bright patch of Tombaugh Regio are both covered in methane ice, while the mid-tones are not. The dark patches south of the equator are also methane, but from their dark color, they are clearly not the same. The mission scientists haven’t explained this yet, but I suspect these are regions where methane ice has been turned into a tar-like substance called tholins by exposure to ultraviolet light from the Sun. This would indicate a much older surface.

Charon’s Young Surface

Pluto's largest moon, Charon. Credit: NASA.

Pluto’s largest moon, Charon. Credit: NASA.

Pluto’s largest moon, Charon, is also full of surprises. My money is on tholins again for the dark spot at the north pole and it appears to be a thin layer, since there are bright white crates blasted into it. But the rest of the surface is surprisingly bright and is probably made of water ice. This isn’t too unexpected. We assume that Charon formed in a giant impact like our own moon, then molecules like nitrogen, methane, and carbon monoxide that would form an atmosphere and other types of ice and frost would have been blasted away into space. The surprise is how few impact craters there are. That suggests that the surface of the moon is very young. The most likely reason for that is if the moon has cryovolcanoes that churn up new layers of ice to the surface, but Charon is small and has no tidal heating like the moons of the gas giants, so it was not expected to have volcanoes. The volcanoes would have to be powered by radioactive decay of natural uranium and thorium in Charon’s core. Charon also has canyons several times deeper than the Grand Canyon.

Pluto’s Rugged Terrain

Closeup of the equatorial regions of Pluto. Credit: NASA.

Closeup of the equatorial regions of Pluto. Credit: NASA.

This is a close-up photo of the part of Pluto near the bottom of the picture, southwest of Tombaugh Regio. The big surprise here is that Pluto looks nothing like Neptune’s moon, Triton, which was thought to be very similar to it. Triton is weird-looking, but it’s flat. But this mountain range on Pluto is 11,000 feet high. On Earth, they would rival the Rockies or the Alps. Being that high, they have to be made of water ice. There also are no identifiable craters in this picture. That means the surface is only about 100 million years old, which is a big deal. That’s as young as most of Earth’s surface. If ice volcanoes are the cause, as we suspect, that means Pluto is as volcanically active as Earth!

We’ll have more pictures on Friday, and I’m definitely looking forward to them.

About Alex R. Howe

I'm a full-time astrophysicist and a part-time science fiction writer.
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