Justin Cowart is a Ph.D. candidate studying Martian geology and remote sensing techniques at Stony Brook University in New York. Justin's research interests lie in exploring the Martian rock record, particularly rocks formed at times when no rocks of similar age on Earth have survived. Justin has had a lifelong interest in exploring space, and he has satisfied that curiosity by looking at the images returned by space missions. He got his start in remote sensing by reprocessing archival data to find aesthetically-pleasing images that escaped public release at the time of the mission. He can be found on Twitter as @jccwrt, and on Flickr.
Heavy frost deposits coat the ground in and around the 139-kilometer diameter (86-mile diameter) Hooke crater in this Mars Express image. The frost serves as a reminder that Mars still possesses water that moves dynamically between the atmosphere and the surface, mostly in the form of ice and vapor. At present, Mars has thick water-ice polar caps and icy clouds. In many locations, temperatures get low enough overnight for the relative humidity to reach 100 percent, and frost forms on the ground as water vapor condenses. As water has moved around with Mars’ shifting climate over its long history, there may have been many periods of wetting and drying all over the planet.