'WATER-BASED LAVA' ON PLUTO'S MOON?

 Pluto's moon Charon is so large that some astronomers have called Pluto and Charon a "double-planet." Could Charon be just as interesting as Pluto? Images just received from NASA's New Horizons spacecraft suggest that it is. When New Horizons hurtled past the Pluto-Charon system last July, it saw a canyon system stretching more than 1,000 miles across Charon's icy face. Four times as long as the Grand Canyon, and twice as deep in places, these faults and canyons indicate a titanic geological upheaval in Charon's past:

"It looks like the entire crust of Charon has been split open," says John Spencer, a member of the New Horizons Science Team from the Southwest Research Institute. "With respect to its size relative to Charon, this feature is much like the vast Valles Marineris canyon system on Mars."

The pictures also show plains south of the Charon's canyon with fewer large craters than regions to the north. This means the southern plains are younger. The smoothness of the plains, as well as their grooves and faint ridges, are clear signs of wide-scale resurfacing:

One possibility for the smooth surface is a kind of cold volcanic activity, called cryovolcanism. "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," says Paul Schenk, a New Horizons team member from the Lunar and Planetary Institute in Houston.

More images and data are in the offing as New Horizons continues to transmit data, stored on its digital recorders, over the next year. As that happens, "I predict Charon's story will become even more amazing!" says mission Project Scientist Hal Weaver, of the Johns Hopkins University Applied Physics Laboratory. Stay tuned.