Move over Pluto, it's time for Charon to step into the limelight.
In new high-resolution observations to be transmitted to Earth from NASA's New Horizons mission, it's Pluto's largest moon, not the famous dwarf planet, that is getting all the attention. In the stunning imagery is never-before seen detail in the moon's landscape, including a huge valley that zigzags across Charon's face, testament to a savagely violent history.
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Charon is around half the diameter of Pluto, making it the largest moon relative to the world it is orbiting in the solar system. In fact, their orbital dance is so extreme that as Charon orbits, it causes Pluto to wobble wildly. Like a hammer thrower spinning on the spot, the center of the system's gravity is located above Pluto's surface, prompting calls to classify Pluto and Charon a "binary planet" - the largest example of its kind in the solar system (there are also several asteroids that are binaries).
But planetary classifications to one side, this new view of Charon shows a fascinating world in its own right, complete with stunning craters, interesting geological features and a dramatically cracked crust that has surprised New Horizons scientists.
"It looks like the entire crust of Charon has been split open," said John Spencer, deputy lead for GGI at the Southwest Research Institute in Boulder, Colo. "With respect to its size relative to Charon, this feature is much like the vast Valles Marineris canyon system on Mars."
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Before the New Horizons encounter with the Pluto system on July 14, planetary scientists assumed that Charon's surface would be fairly straight forward; a rocky object pockmarked with craters. While there certainly are craters, there are huge surface variations. Of particular note is the apparent age disparity between the younger plains south of Charon's valley and the more ancient craters of the north.
At first glance, it could be that some process, such as cryovolcansim, is actively resurfacing the southern plains, making the landscape appear younger. "The team is discussing the possibility that an internal water ocean could have frozen long ago, and the resulting volume change could have led to Charon cracking open, allowing water-based lavas to reach the surface at that time," said Paul Schenk, New Horizons team member from the Lunar and Planetary Institute in Houston, Texas.
"We thought the probability of seeing such interesting features on this satellite of a world at the far edge of our solar system was low," added Ross Beyer, an affiliate of the New Horizons Geology, Geophysics and Imaging (GGI) team from the SETI Institute and NASA Ames Research Center in Mountain View, Calif., "but I couldn't be more delighted with what we see."
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Like Pluto's surprisingly complex and dynamic surface, it seems that even Charon, although smaller, has a story to tell. It will likely be some time before we fully understand its nature, particularly the story behind that fascinating 1,000 mile-long (possibly longer) chasm, but one thing is immediately clear: both Pluto and Charon have completely surpassed everyone's expectations. They truly represent a different class of world that evolved in the frozen hinterland of the solar system and the science that New Horizons is beaming back is revealing just how alien this region truly is.