An ancient, watery Mars was not always an acid bath

[v_gowda]

This is an article from sci Am:<br /><br />In one of the less subtle episodes of the original Star Trek series, hippies hijack the Enterprise to get to a planet that looks like paradise but turns out to be a grim, acid-soaked purgatory. Over the past two years, a similar allegory has played itself out in Mars science. Drawn to Mars largely by signs of past Earth-like conditions, researchers have finally found definitive relics of gently lapping seas and balmier skies: in particular, deposits of sulfate salts. To form those sulfates, though, the ancient seas must have been acidic enough to burn off skin. <br /><br />But a different tale is told by another class of minerals, fully mapped only recently: clays. They suggest that even before the era of the sulfates, Mars was drenched in water safe enough to dunk a hand in. "The clays indicate alteration with a lot of water," says François Poulet of the University of Paris-South, a member of the discovery team. "The sulfate indicates a second step in the climate of Mars."<br />The Viking missions of the mid-1970s and subsequent ground-based telescopic observations saw hints of clay, but they were ambiguous, and mid-infrared spectrometers on NASA's orbiting Mars Global Surveyor and Mars Odyssey probes came up blank. The OMEGA spectrometer on the European Space Agency's Mars Express orbiter has gone where no spectrometer has gone before, covering near-infrared wavelengths and offering 10 times the resolution of earlier instruments. It first detected clays (technically called phyllosilicates) last year, but the data were spotty, and some scientists wondered whether the clays were merely superficial layers, the result of gradual weathering rather than thorough soaking. <br /><br />At a September meeting of the American Astronomical Society, Poulet described how clays now show up on numerous small and widely dispersed outcrops, as well as in crater debris and rock strata--evidence for a substantial deposit. The terrain appears to be

 

[JonClarke]

Nice article. I must confess I find the global acid model a bit to simplistic.<br /><br />One possibility is that the carbonates are all underground, formed by water-rock interaction in the subsurface. The surface acidity (which may not be everywhere anyway), is a surface phenomenon.<br /><br />Jon<br /> <div class="Discussion_UserSignature"> <p><em>Whether we become a multi-planet species with unlimited horizons, or are forever confined to Earth will be decided in the twenty-first century amid the vast plains, rugged canyons and lofty mountains of Mars</em>  Arthur Clarke</p> </div>

 

[bonzelite]

what is "novel chemistry?;" the article does not expound on this. <br /><br />so the premise of "water that burns skin off" must imply sulfuric acid? like on Venus?

 

[JonClarke]

The adundance of sulphate means that if you have acidity it will be sulphuric acid. Conversely, if chloride were dominant you could call it hydrochloric. There is a certain irony in that the chief developer of the surface acidity idea was called "Burns" <img src="/images/icons/smile.gif" />.<br /><br />I think the exotic chemistry comment was a CYA exercise based on the surprises from the Viking mission.<br /><br />But as I said, I do find the supposed ubiquitous acidity very glib. If there is one lesson we have learned from 40 years of mars exploration is that more Mars is both more complex and surprising than we expect.<br /><br />Jon <div class="Discussion_UserSignature"> <p><em>Whether we become a multi-planet species with unlimited horizons, or are forever confined to Earth will be decided in the twenty-first century amid the vast plains, rugged canyons and lofty mountains of Mars</em>  Arthur Clarke</p> </div>

 

[bonzelite]

indeed, mars is a tough nut to crack. it seems always just beyond grasp of any new data. as well, there must be so much data from the MERs that it may be 3 or 5 years before some of it is actually analyzed.

 

[paulanderson]

Yes, good article. I had blogged it already, and thought that I had posted it here somewhere also, but I looked again and guess I didn't, so glad somebody did! This is exactly why Mars Express' findings are important, as I've said before.<br /><br />Re the lack of carbonates though, as mentioned in the article, I keep hearing this, but what about the traces Spirit found at the beginning of the mission? That same MER update from early 2004 mentioned low-level global deposits also, so there <i>are</i> carbonates on Mars, although just traces found so far apparently (and in some of the Martian meteorites as well). I need to find the link again, but it's on the main MER web site, one of the press releases. Yet I still hear people say there are none at all, which is seemingly inaccurate. Do you have happen to have any other information on this, Jon? Thanks.<br />

 

[JonClarke]

Hi Paul<br /><br />As I understand it (from memory) there is a couple of 2% carbonate in the dust. Some of the Martian meteorites have a few percent carbonate alteration as well. But people were expecting a lot more from a planet with an apparent watery past. The expectation was that there would be thick beds of carbonates, like terrestrial limestones and dolomostones, and also extensive carbonate alteration of bedrock. These has not been seen. <br /><br />There are of course many explanations.<br /><br />1) The carbonates were never there because the water was too acid (possible on a local scale but I find it hard to imagine for the whole planet).<br /><br />2) Mars was never wet (which means we have to find alternate explanations for all the watery features, I find this too hard to imagine).<br /><br />3) The bulk of the carbonates are in fact underground, the surface chemical environment is not indiactive of the planet as a whole (this would be consistrent with the altered meteorites and the liklihood that most of the water-rock interaction has been underground).<br /><br />4) Mars has evolved different to earth - early terrestrial waters were rich in carbonate but low in sulphate. Maybe Mars was the opposite (mind you its worth noting that carbonates are rare on earth in rocks older than 2.5 Ga)<br /><br />Martian dust provides a reasonable bulk approximation of the composition of the surface. If carbonates make up 2% of the dust then they make up 2% of the surface. Whether this 2% is disseminated across the surface outcrops of Mars or whether locally there are small areas that approach terrestrial limestones in compostion (possibly obscured from prying satellites by weathered or dust covered surfaces) we don't know.<br /><br />Jon <div class="Discussion_UserSignature"> <p><em>Whether we become a multi-planet species with unlimited horizons, or are forever confined to Earth will be decided in the twenty-first century amid the vast plains, rugged canyons and lofty mountains of Mars</em>  Arthur Clarke</p> </div>