15 March 2008
Salt and vinegar potato chips.
Ok, not really: there are no potatoes on Mars. On the other hand, there is mounting evidence that Mars is and was a salty and acidic place. The salts are not generally table salt, and the acid was likely sulfuric rather than acetic, but you get the idea.
There were several talks today about experimenting with brines (salty solutions) to see if they could explain some of the observations of Mars. Jeff Moore described some ongoing experiments with salty solutions generated by mixing water with Mars soil simulants. He allowed the brines to evaporate under an atmosphere similar to the current Mars atmosphere (thing CO2) and also under an acidic SO2-based atmosphere that may better represent early Mars. By looking carefully at the sorts of crystals that formed, he showed that the brine that evaporated under an acidic, sulfur-rich atmosphere had more magnesium-sulfates, and matched more closely with the minerals seen by the Opportunity rover at Meridiani.
A second talk about salty solutions, given by Vincent Chevrier, studied how brines can act as antifreeze and permit liquid water on Mars. Currently the temperature and atmospheric pressure on Mars are too low, and water will either freeze or evaporate rapidly. However, anyone who lives in a wintry climate knows that salt can keep water liquid to temperatures well below zero. Chevrier showed that water mixed with sulfate salts can remain liquid down to temperatures of -72 degrees Celsius (-98 degrees Fahrenheit). He also showed that very salty solutions can reduce the rate of evaporation by up to 50 times. Chevrier suggested that this may mean that gullies on Mars are indeed formed by liquid water.
Carl Allen asked an excellent question following Chevrier’s presentation: If gullies are formed by these sulfate brines, shouldn’t we see sulfate signatures in the spectra? Chevrier said yes, but had not looked for the signature yet. He also suggested that the lack of a signature would not necessarily mean that brines were not involved because there are several plausible ways that the salty water could seep away, leaving the gully signature-free.
All of these serious laboratory studies are well and good, but really, the important thing here is that we have discovered a new Mars analog, and it’s available at your local supermarket!