The Planet Mars
Left: Gullies in the northern wall of an impact crater in Terra
Sirenum at 39.1°S, 166.1°W. The image is approximately 3 km
across. (Synthetic colour portion of Mars Orbiter Camera image
NASA/ Malin Space Science Systems).
It is widely believed that early climate of Mars, before about 3.5
billion years ago, would have
needed to be warmer in order to produce certain geological features
that appear to have been eroded by water,
networks and heavily degraded impact craters. But exactly how the
produced warmer conditions is still an open question.
A key area of research is looking at new geochemical, atmospheric and geological data from spacecraft to try to determine the evolutionary history of the geology and atmosphere of Mars [1,2]. This provides the context for the habitability of Mars.
For the last 3.5 billion years, it is likely that Mars has been cold and dry so that geologically recent outflow channels and gullies (above) were probably formed by fluid release mechanisms that have not depended upon a warm climate. The influence of wind in shaping the landscape of Mars during this time is another research interest.
 D.C. Catling, S. E. Wood, C. Leovy, D. R. Montgomery, H. Greenberg, C. R. Glein, J. M. Moore, Light-toned layered deposits in Juventae Chasma, Mars, Icarus, 181, 26-51, 2006.
 G. M. Marion, D. C. Catling , and J. S. Kargel, Modeling aqueous ferrous iron chemistry at low temperatures with application to Mars, Geochem. Cosmochem. Acta, 67, 4251-4266, 2003.