The pictures come from Nasa's Mars Global Surveyor (MGS) spacecraft, which is currently in orbit around the Red Planet.
The pictures reveal channels in the peaks of sand dunes within one of the planet's southern craters.
The pictures come from Nasa's Mars Global Surveyor (MGS) spacecraft, which is currently in orbit around the Red Planet.
Earlier this year, scientists at the US space agency and Malin Space Science Systems, who operate MGS, presented photographic evidence pointing towards the presence of recent, running water on Mars. "Recent" in this sense means within the last two million years.
The announcement, which ran counter to prevailing theories about the presence of water on the Red Planet, caused a sensation. The "discovery" gave fresh impetus to Nasa exploration plans that were under threat at the time because of the loss of two probes.
Hale crater
The Mars Global Surveyor made the observations on 10 November. The top of the picture shows peaks up to 630 metres (2,070 feet) above the crater floor.
Small gullies can be seen on the slopes of some of the largest peaks. Nasa scientists believe these channels may have been carved by running water.
The new pictures add to a growing body of evidence gleaned by the MGS which suggests that water could exist in a porous layer of rock buried just below the Martian surface.
If liquid water does still flow on Mars, and some experts remain sceptical, the planet's southern hemisphere would be a good place to look. More than 90% of the gullies are located there, in the cooler areas away from sunlight.
Martian autumn
Winter in the Martian southern hemisphere begins in mid-December. Over the next few months, Nasa scientists will examine closely new pictures of the planet in an attempt to bolster their evidence.
Liquid water is the key ingredient for supporting life. If the discovery were confirmed, it would have profound implications for the chance of finding existing, microbial extra-terrestrial life.
But some experts are cautious about the findings. It had been thought that water on Mars was in the form of ice below the surface and unlikely to run free on the surface.
Mars enthusiasts will be awaiting eagerly the opportunity, in the next few years, to place a lander on the surface of the planet in an attempt to resolve the question one way or the other.