Giant Mars crater hints at steamy past

Modern Mars may be a frozen wasteland, but it has a hot and steamy past. NASA's Opportunity rover has started examining its most significant target yet, Mars's giant Endeavour crater. The initial results suggest the structure was once exposed to hot water.

Opportunity drove for three years before reaching the 22-kilometre-wide crater. Its rim exposes rocks from the earliest epoch of Martian history, when liquid water was abundant.