By Ron Cowen
A newfound reservoir of dry ice on Mars suggests that the planet’s surface has been wetter in the relatively recent past, though not necessarily warmer than it is today.
The new study adds to evidence that Mars once had a carbon dioxide atmosphere thick enough to keep liquid water on the surface from evaporating. It’s unclear whether the planet would have been hospitable for life, however, because temperatures on Mars may actually have been slightly colder during times when the atmosphere had a greater amount of carbon dioxide.
Roger Phillips of the Southwest Research Institute in Boulder, Colo., and his colleagues base their findings on radar studies by the Mars Reconnaissance Orbiter of the layered deposits at Mars’ south polar cap. Earlier studies had indicated that a veneer of frozen carbon dioxide sits atop part of the cap with a thin layer of water ice beneath it. But a detailed analysis of radar reflected from different layers of the cap reveals that beneath the frozen water lies a volume of carbon dioxide ice 30 times greater than previously estimated, the team reports online April 21 in Science.