Taking the Life Out of Titan

摘要

Is Saturn's big, haze-shrouded moon Titan dead or alive? Many planetary geologists say alive. Radar images from the Cassini spacecraft show what look like volcanoes thought to spew icy "lavas" and pump methane into Titan's atmosphere. But other Cassini data have led a group of planetary physicists to a different view. They report this week that Titan appears to be encased in a shell of rock-hard ice tens of kilometers thick-perhaps too rigid to allow ice magma to rise from the depths.