These mounds in the Acidalia Planitia region of Mars figure among the proposed future Mars landing sites. The mounds are believed to be "mud" volcanoes formed when gas, liquid and well, mud got forced to the surface. For scientists, these sediments are particularly intriguing as they might contain organic materials pointing to the history - or continuation - of microbial life on Mars.
The bright material in this image is likely water frost. Temperatures at this latitude probably do not get cold enough for carbon dioxide to condense. The crater in this image is located in Terra Sirenum in the Southern hemisphere of Mars.
The Holden Crater on Mars may once have been a lake. Scientists report that the crater contains "some of the best-exposed lake deposits and ancient megabreccia known on Mars," according to Alfred McEwen of the UA's Lunar and Planetary Laboratory. "Both contain minerals that formed in the presence of water and mark potentially habitable environments. This would be an excellent place to send a rover or sample-return mission to make major advances in understanding if Mars supported life."
Another area of interest that one day may be visited by the Mars rover - the rocky mesas of Nilosyrtis Mensae. The region is rocky and any visit would have to start in a flatter adjacent area. Even then, scientists say an acceptable landing site might be too far away from the mesas to reach the area. But it's worth a shot as the area is of keen interest. Spectrometer readings from the Mars Express and MRO spacecraft have detected clay minerals which may contain clues about the possibility of life on ancient Mars.
This impact basin, called the Columbus Crater, has seen a lot of change during its days. Scientists believe the crater is quite old and thus has suffered from erosion that subsequently deposited materials on the crater floor. How the sediments filled the basin, however, remains unknown. In the accompanying image, you can make out the sedimentary deposits by their bright stripes in the picture.
The partially defrosted Richardson Crater Dunes reveals large patches of carbon dioxide frost. You can also see channels formed by the erosion of carbon dioxide gas,
The Santa Maria crater is going to get a visit from the Mars Rover sometime soon. Spectrum readings suggest what might be a water-bearing sulfate mineral in the areas. Although the "Opportunity" rover has detected such minerals on the surface during its nearly seven years on Mars, none have been detected from orbit at a place visited so far by the Opportunity.
Caves on Mars - any spelunkers in the audience?
NASA's Mars Exploration Rover Opportunity has a view of the Santa Maria crater from the western edge of this crater, and this view is eastward across the crater.
East Rim of the Endeavour Crater in Opportunity's view. The rover is headed for a portion of the crater's western rim, which is not visible in this image.