The valleys, channels and deltas viewed from orbit have long been thought to be the work of water erosion, but it is Nasa's latest rover, Curiosity, that has provided the "ground truth".
Researchers report its observations of rounded pebbles on the floor of the Red Planet's 150km-wide Gale Crater.
Their smooth appearance is identical to gravels found in rivers on Earth.
Rock fragments that bounce along the bottom of a stream of water will have their edges knocked off, and when these pebbles finally come to rest they will often align in a characteristic overlapping fashion.
Curiosity has pictured these features in a number of rock outcrops at the base of Gale Crater.
It is confirmation that water has played its part in sculpting not only this huge equatorial bowl but by implication many of the other landforms seen on the planet.
Using its Chemcam remote-sensing laser, the rover was able to detect feldspar in the lighter toned clasts.Feldspar is a common mineral on Earth that weathers quickly in the presence of water.
This suggests past conditions were not overly wet and that the pebbles were carried only a relatively short distance - probably no more than 10-15km. This fits with satellite observations of what appears to be a nearby network of old rivers or streams spreading away from the mouth of a channel that cuts through the northern rim of Gale Crater.
Via Dr. Stefan Gruenwald