I share Emily’s slight disquiet over the spin applied to the latest (and possibly last) results from Mars Global Surveyer. This is not to say that pictures like this (source) don’t get me very excited:
However, let’s be clear on what we can say for sure. The deposit which appears in the later photo on the top right, and is magnified in the bottom right image, has features very suggestive of fluid-like flow: it appears to be diverted around elevated topography, and fans out at the end. And we strongly suspect that any water on Mars will have very high concentrations of mineral salts, meaning that the lighter colour of the new feature might plausibly be explained by these salts being left behind on the surface when flowing water sublimes away in Mars’s puny atmosphere. However, in the absence of spectrometry to analyse the composition, there are still alternatives to water, such as
liquid carbon dioxide, or dust flows.
In the midst of all this excitement I wondered whether there was any more data coming in from MARSIS, the radar instrument on Mars Express. It’s been more than a year since I blogged about preliminary indications of subsurface water ice beneath Chryse Planitia (at mid-latitudes, like the crater gulleys being scrutinised by NASA). Very little seems to have been released since; the only reference I found was a throwaway remark in this nice summary article:
"MARSIS has shown that many of the upper layers of Mars contain water ice," says Jeffrey Plaut of the Jet Propulsion Laboratory, Pasadena, who is the co-Principal Investigator on the MARSIS experiment.
Interestingly, most of the article is discussing spectrometry results which show how early standing water on Mars seems to have been fairly quickly locked away in clay minerals, sulphates, and red ferric oxides. But pure water may still be around, in the form of subsurface permafrost which in some places may be quite close to the surface. The Global Surveyor pictures hint that this arrangement may not be completely stable. And dynamic processes, even on a small scale, are exciting; change leads to disturbances from equilibrium, and interesting chemistry, which are the sorts of things that life thrives on.
Either way, results like this show exactly how the decision to send a succession of probes to Mars to place it under close, continuous observation is paying real scientific dividends.