On Google Earth Hacks, an overlay of a just-discovered mega crater under the ice of Wilkes Land, Antarctica. It’s 500 kilometers wide — larger than the current record-holder, the 300-km wide Vredefort crater in South Africa — and it is the new front-runner for the cause of the Permian-Triassic extinction 250 million years ago. Scientists also suspect it may have begun the breakup of Gondwana land. Read more in this Science Daily article from June 1, 2006. (On site confirmation is still pending, however. Some people get all the fun:-)
How do you find a crater under kilometers of ice? You use gravity sensing satellites, like NASA’s two GRACE satellites, which are so sensitive they can measure the gravitational effect of heavy rainfall.