NASA scientists think they've developed a strong case that liquid water created the strange gullies discovered on Mars a few years ago. These gullies might indicate underground sites of water, and could be a good place to search for life. Although Mars' environment is too cold, dry and low pressure to support liquid water, it could last a little while as it escaped from an underground reservoir. The lack of debris fields at the ends of these gullies suggests the water froze or evaporated before it reached the bottom.