Water flowed on the surface of Mars as recently as 200,000 years ago, new research suggests.
A young crater in the planet's southern hemisphere contains well-preserved gullies and sediment deposits thought to have been formed by water.
Scientists studying the crater estimated it to be no more than about 200,000 years old, so the water features must have appeared since then.
The crater formed long after the most recent proposed ice age on Mars, which ended some 400,000 years ago.
Lead scientist Dr Andreas Johnsson, from the University of Gothenburg in Sweden, said: "Gullies are common on Mars but the ones which have been studied previously are older, and the sediments where they have formed are associated with the most recent ice age.
"Our study crater on Mars is far too young to have been influenced by the conditions that were prevalent then.
"This suggests that the meltwater-related processes that formed these deposits have been exceptionally effective also in more recent times."
Features characteristic of debris flows on Earth caused by material being carried and then deposited by fast-moving water were seen in the crater.
The Martian landforms were compared with known debris flows on the Norwegian Svalbard islands in the Arctic Ocean.
"Our fieldwork on Svalbard confirmed our interpretation of the Martian deposits," said Dr Johnsson, whose findings appear in the scientific journal ICARUS.
"What surprised us was that the crater in which these debris flows have formed is so young."
The study crater is situated in the mid-latitudes of the Martian southern hemisphere and superimposed on the "rampart ejecta" of a nearby larger crater.
Rampart ejecta, which display flower-like features, are believed to be the result of a meteor impact on wet or icy ground.
The scientists first thought the recent water flow features had come from preserved ice within the rampart ejecta.
However, structures such as faults or fractures that could have acted as conduits for the meltwater were missing.
"It is more likely that the water has come from melting snow packs, when the conditions were favourable for snow formation," said Dr Johnsson.
"This is possible since the orbital axis of Mars was more tilted in the past than it is today."