Berlin, September 25 : Scientists have presented evidence that lake deposits once formed inside impact craters on Mars, which may have been fed by short-lived rivers that were, in turn, fed by precipitation, suggesting that it used to rain on the Red Planet.
These are the findings of an international team of researchers led by Ernst Hauber of the German Aerospace Center, who analyzed the latest image data of the Martian surface.
They discovered delta deposits in these images, relatively unaffected by erosion, inside the craters.
The scientists explored the Xanthe Terra area located near the equator in the Martian highlands.
"For years, scientists have been suspecting that the current appearance of the landscape has, in part, been shaped by rivers that cut into the surface," explained Hauber.
"We can see layered sediments where these valleys open into impact craters. The shape of certain sediments is typical for deltas formed in standing water," he added.
The Xanthe Terra highlands in the equatorial region of Mars are traversed by deeply incised valleys. Scientists have suspected for a long time that these were formed by water erosion.
A particularly beautiful delta can be found here in a small crater with a diameter of only five kilometres.
The Nanedi river opens into the crater from the south, where the sedimentary material is distributed over a fan-shaped area. The crater is almost completely filled with sediments.
Topographic data derived from the stereo images recorded by the HRSC camera show that the layer of material is at least 50 metres thick and the deposits cover an area of about 23 square kilometres.
Very thin layers can be seen along the edge of the deposits. Such thin layers are also typical for deltas on Earth.
A particularly interesting discovery is the small valley that leaves the crater towards the east, which provides evidence that water must have indeed been "standing" in the crater.
"If the water flowed into the crater and back out again, it must have filled it up as well," said Hauber. "In this and in a few other cases, we are fairly certain that there were lakes on Mars," he added.
The researchers can also narrow down the period when the craters were filled with lakes. In order to do so, they analyse the statistical distribution of impact craters of different sizes.
The crater counts revealed that water was flowing through the valleys between about 4 and 3.8 billion years ago. The valleys themselves could have formed relatively fast.
According to the research, it would not have taken more than a few hundred thousand years for the deltas to reach their current dimensions. Compared to other geological timescales, especially in planetary geology, this is a very short period of time.
Thus, there must have been precipitation on early Mars.