Martian water may flow on sunny summer slopes
5 August 2011 Last updated at 01:39 BST
Striking new images from the mountains of Mars may be the best evidence yet of flowing, liquid water, an essential ingredient for life.
The findings, reported on Thursday in the journal Science, come from a joint US-Swiss study.
A striking sequence of images from the Mars Reconnaissance Orbiter show many long, dark "tendrils" a few metres wide emerging between rocky outcrops and flowing hundreds of metres down steep slopes towards the plains below.
They appear on hillsides warmed by the summer sun, flow around obstacles and sometimes split or merge, but when winter returns, the tendrils fade away. The BBC's Daniel Griffiths reports.