NASA's Curiosity rover has begun exploring a new region of Mars, one that could reveal more about when liquid water disappeared once and for all from the Red Planet's surface. Billions of years ago, Mars was much wetter and probably warmer than it is today. Curiosity is getting a new look into that more Earth-like past as it drives along and eventually crosses the Gediz Vallis channel, a winding, snake-like feature that—from space, at least—appears to have been carved by an ancient river.