Giant Mars crater hints at steamy past

摘要

Modern Mars may be a frozen wasteland, but it has a hot and steamy past. A Mars rover's first stab at analysing a giant crater suggests the structure was once exposed to hot water. In August, NASA's rover Opportunity reached its most significant target yet, the 22-kilometre-wide Endeavour crater. Its rim exposes rocks from the earliest epoch of Martian history, when liquid water was abundant. Opportunity started by investigating a rock about 1 metre across, named Tisdale 2, and found large quantities of zinc, more than in any other rock examined by Opportunity or its now defunct sister rover, Spirit.