Ancient Mars may have been sufficiently warmed by greenhouse gases in its atmosphere to permit liquid water to flow on its surface, according to a study published online in Nature Geoscience. The existence of valley networks preserved on ancient terrains -- seemingly carved about 4 billion years ago by flowing water -- has been difficult to reconcile with a dim young Sun that would have rendered Mars too cold for liquid water to exist.
Jim Kasting and colleagues used a climate model to demonstrate that an atmosphere containing more than 5% of the greenhouse gas molecular hydrogen, in addition to water vapour and carbon dioxide, could have raised the surface temperature of early Mars above water’s freezing point. Climate models had previously shown that the greenhouse effect from carbon dioxide and water vapour alone would have been insufficient to warm the planet.
The researchers suggest that high concentrations of atmospheric molecular hydrogen could have been supplied by vigorous volcanic outgassing.