Scientists have found what they believe may be evidence of flowing water on Mars.
NASA researchers say images taken by the Mars Reconnaissance Orbiter show clusters of dark lines on some slopes on the planet.
The "tendrils", a few metres wide, emerge between rocky outcrops and flow hundreds of metres down steep slopes towards the plains below, the BBC reports.
They appear on hillsides warmed by the summer sun, flow around obstacles and sometimes split or merge, but fade away when winter returns.
The researchers say this suggests that they are made of thawing mud.
The scientists believe that if there is liquid water on Mars, it would be highly salty and lie beneath the surface.
That would explain why it would not freeze in surface temperatures, which can fall to -128 degrees Celsius.
NASA first found signs of water on Mars more than a decade ago, but earlier indications were that any existing water would be frozen and concentrated at the poles.