[X] My Assistant

[dvandorn]

As I recall, the ambiguous results of the Viking landers' life detection experiments were explained at the time by postulating that the surface soils are highly enriched with extremely oxidized clays (I seem to recall descriptions of clays enriched with peroxides).

Nearly identical results were seen at both V1 and V2 sites, so, assuming that the results are explained by what was called "exotic soil chemistry," this chemistry would have to be widespread on Mars.

We now have some very good elemental analyses of the Martian soils, both from orbit and ground-truth from the MER rovers. In these analyses, clays seem not at all widespread, only appearing in very, very old outcrops that were presumably laid down during a very short geological timeframe during which non-acidic water was common on the Martian surface.

Soils in the Viking landing sites would appear, from the more advanced sensors we've flown since Viking, to be basaltic with admixtures of ferrous sulphates. Not exactly the exotic chemistry required to explain the Viking results.

So, the million-dollar question seems to be: if the Viking experiments can only be explained by *either* biotic processes that do not involve what we always considered the pre-requisite organic molecules, *or* by ubiquitous exotic chemistry in the soils that we're simply not seeing with more advanced instruments, which theory are we forced to accept as fact?

If neither, then what theory *does* account for the Viking results?

-the other Doug

[Guest_BruceMoomaw_*]

David Des Marais' discussion in the Jan. 2005 "Geochemical News" that I mentioned on another thread ( http://gs.wustl.edu/archives/gn/gn122.pdf, pg. 9-16) contains quite a detailed discussion of the instruments which he regards as crucial to a remote analysis of Martian material by a rover. One is a good detector and analyzer of trace organics -- specifically, a GCMS -- and the other is a "definitive mineralogy analyzer", for which he regards an X-ray diffractometer as being best. MSL '09 will carry both -- but both require a quite sophisticated system for ingesting, grinding up and distributing hard samples like rocks, which the MERs were simply too small to carry. (The proposed follow-up "Viking 3", interestingly, probably would have carried all of these; but even if it was mobile, its range would have been far more limited than that of MSL, or for that matter of the MERs.)

And neither of these instruments would do a good job of analyzing Martian oxidants, which are very unstable and will require specially designed analysis techniques to nail them down precisely. Wet chemistry tests -- of the sort that Phoenix will do -- will probably be best for that purpose; I don't know how good MSL will be at analyzing them, although its GCMS may provide some data. In fact, oxidants probably cannot even be returned successfully in Mars sample-return missions -- they're too unstable and would break down en route, without constant reapplication of the Martian environmental processes that created them in the first place. Thus they will likely require in-situ analysis.

About a decade ago, NASA published a very authoritative guide to the sorts of analyses that different instruments on planetary landers can do -- if I can track the damn thing down. At the moment I can't find it on Google, but I know I have a copy of it somewhere.