Is Mars still wet?

A few weeks following a fascinating report of thick deposits of water ice detected in small, permanently shaded craters on the moon, a potentially much bigger story about liquid water on Mars has begun to trickle out of the news agencies.

Evidence of active gullies on Mars? (source: HiRISE/NASA Ames)
Evidence of water still flowing on Mars? (source: HiRISE/NASA Ames)

The latest news follows a paper published in Geophysical Research Letters, in which a group of planetologists led by Dennis Reiss present images of small gully-like features on the Russell crater dune field. Over a period of two years the researchers observed the lengthening by some tens of metres of one particular gully channel, and argue that the change is best explained by a transient melting of small amounts of water ice that triggers brief flows of sand and liquid water slurry.

While the data presented by Reiss and his colleagues are interesting enough and sufficiently well presented to make it into a peer-reviewed journal in letter form, it isn’t the first time that scientists have speculated about liquid water still flowing on the planet, if only for brief periods.

The report is intriguing, but the problem is the lack of evidence for geological activity on Mars that could drive the hot springs or similar necessary to inject liquid water onto the surface of a frigid and largely airless world. There are plausible alternative hypotheses which could explain small features that resemble active water channels. “Inverted relief”, for example, in which once below-ground structures end up on the surface following erosion.

It will be interesting to see how this story plays out. For now, however, I think we should avoid reading too much into it and getting overexcited about the possibility of a still watery Mars.

Further reading: Reiss et al., “Evidence for present day gully activity on the Russell crater dune field, Mars”, Geophys. Res. Lett. 37, L06203 (2010)