Another neglected story from last week: there was a big news splash about two articles that appeared in Nature about Mars Exploration Rover Opportunity's landing site. The articles suggest two theories for the formation of the layered sulfur-rich deposits at Meridiani Planum that do not involve standing liquid water. One paper, "Impact origin of sediments at the Opportunity landing site on Mars," proposes that the sediments could actually be "a ground-hugging turbulent flow of rock fragments, salts, sulphides, brines and ice produced by meteorite impact." The other paper, "A volcanic environment for bedrock diagenesis at Meridiani Planum on Mars," says that the sediments' origin "involves deposition of volcanic ash followed by reaction with condensed sulphur dioxide- and water-bearing vapours emitted from fumaroles."
These papers are answers to an excellent question that anyone who has been following Opportunity should be asking. That question is, "is there anything else besides liquid water that could explain the features that Opportunity has been observing?" By suggesting two alternative theories, these teams of scientists are providing sets of predictions for what else Opportunity should have observed that differ from what Steve Squyres and his team are predicting. I expect Squyres et al will go back in to their data and look for ways to falsify these papers.
Unfortunately, the publication of these papers was heralded by a lot of media hoopla that basically said "those rover guys are wrong, and they've been wrong for almost two years." While it is certainly possible (in fact likely) that portions at least of the rover teams' theories and interpretations of their data will turn out to be wrong, these two papers by themselves don't prove it. Instead, they just suggest alternative lines of investigation. I hope to see constructive debate on this topic at future science meetings, in which many researchers outline the predictions that arise from the three different theories (liquid water origin, impact origin, volcanic origin) and then see how well the observations match up with the predictions. What I hope not to see is a lot of accusations in the media saying "the other guys are wrong." That's just not very constructive. For his part, Squyres recommended in his most recent Mission Update that the curious check out the papers that the team published recently in Earth and Planetary Science Letters. This is a scientific journal so most of the articles are not available for free (unless you go down to your local university's science library). However, there is a single interesting-sounding article available for free: "An Astrobiological Perspective on Meridiani Planum" (PDF format, 200k) by Andrew Knoll et al.
In the same update, Squyres made the following comments about the status of the problem with Opportunity's arm:
Over at Meridiani, we have now gotten pretty good at operating our balky arm without problems. And we've been at Olympia long enough now that it's probably now the best-imaged place on the entire planet. With all that imaging we've identified several other nearby targets that we'd really like to take a look at. Unfortunately, though, it's still going to be a little while before we can get moving again. While we know how to work the arm, we're still figuring out the best way to stow it. We no longer want to stow it under the front of the vehicle, since a complete motor failure there would incapacitate the arm permanently. Instead, we're looking at "stowing" it somewhere out in front of the vehicle. That sounds easy, but it's something really new... we've never tried driving with the arm deployed, on either planet, so we've got to be very careful. Being very careful means we have to do a lot of calculations and tests on Earth before we're ready to try it on Mars. So it'll still be a little while before we're ready to drive anywhere.