Carbon dioxide and Martian channels

Despite the evidence from the neutron detector on Mars Odyssey for the possible existence of subsurface water on Mars (Water on Mars, August 2002 Earth Pages News) not everyone accepts that minor rills and channels on its surface are due to periodic melting of buried water ice (Water on Mars, July 2000Earth Pages News).  Two small pieces in New Scientist contest that view.  In a letter, Wytse Sikkema of Shell likens them to features carved by turbidity flows (suspensions of solid particles in a fluid, such as avalanches, ash flows and submarine turbidity currents) which they resemble more than stream channels (Sikkema, W. 2003.  Rivers of Dust.  New Scientist, 18 January 2003, p. 24).  Sikkema suggests that the supposed ocean-like basins on the Red Planet are filled with dusts carried by such flows.  Support for such a mechanism emerges from observations of gullying in progress during Mars’ late spring near the poles, when temperatures were too low for liquid water to exist.  Nick Hoffman of the University of Melbourne, suggests that the active gullying that he observed  on successive Mars Global Surveyor images involves rapid vaporisation of CO2 snow and ice to lubricate dust avalanches (Nowack, R. 2003.  Ravines hint at gas avalanches on Mars.  New Scientist, 18 January 2003, p. 14-15).  Hoffman also considers that massive release of gas by boiling of buried CO2 liquid could have carved the much larger valley systems on Mars by massive flows of dust-gas mixtures.  If he is correct, there is no reason to consider Mars either as a haven for early life or one for intrepid astronauts.  Britain’s Beagle 2 probe and two unnamed NASA Mars rovers, due for launch this year, should resolve the issue, but if water is not confirmed, there will be huge disappointment for both teams involved with those missions.

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