The Double Planet

Next week the New Horizons spacecraft falls through (or “flies by”) the Pluto-Charon binary system. This week New Horizons photos reveal dramatic differences between Pluto and Charon, despite their presumed common origin in an interplanetary collision. (By the way, some astronomers — and apparently the New Horizons science team — pronounce “Charon” more like “Charlene”, the name of the wife of Charon’s discoverer, and less like “Karen”).

So close, yet so different: gray Charon (left) and beige Pluto (right) orbit the common center of mass between them forming a double planet. To fully appreciate the image, click on it for a larger version.

So close, yet so different: beige Pluto (left) and gray Charon (right) orbit the common center of mass between them forming a double planet. UPDATED 2015 July 17; click image for a larger version.

We already know spectroscopically that water H2O, methane CH4, nitrogen N2, and carbon monoxide CO ices cover Pluto’s surface (and form its tenuous and dynamic atmosphere). Ultraviolet or UV radiation probably converts nitrogen and methane into reddish, organic tholins CxHyNz. But what causes the patterns of bright ices and dark orangish tholins? By contrast, Charon’s darker surface appears to contain water crystals and ammonia hydrates (NH3)2H2O. Like Triton, the largest moon of Neptune, both Pluto and Charon may have active geysers, which may contribute to the distribution of their surface materials. Stay tuned!

About John F. Lindner

John F. Lindner was born in Sleepy Hollow New York and educated at the University of Vermont and Caltech. He is a professor of physics and astronomy at The College of Wooster. He has enjoyed multiple yearlong sabbaticals at Georgia Tech, University of Portland, and University of Hawai'i. His research interests include nonlinear dynamics, celestial mechanics, and variable stars.
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