Twin Mars craters suggest subsurface water in planet's past

A European spacecraft captured an image of "twin" craters on Mars showing evidence of dramatic underground events possibly involving ice, scientists say. The image taken by the European Space Agency's Mars Express orbiter shows two craters side by side in the Thaumasia Planum region, a large plateau immediately to the south of Valles Marineris, the largest canyon in the Solar System. Both craters are about 30 miles wide and both display an intriguing interior feature of a central pit, a release from ESA's Paris headquarters reported Wednesday. Ideas vary on how such pits may have been formed, scientists say. One idea is that rock or ice melted during the impact drains away through fractures beneath the crater, leaving a central a pit. Another theory is that subsurface ice is rapidly heated during the impact of an asteroid, vaporizing in an explosion that creates a pit surrounded by rocky debris. The twin craters provide evidence the Thaumasia Planum region may have once contained plentiful subsurface water or ice that was liberated during impact events both small and large, scientists said.