On the Possibility of a Persistent Mars Greenhouse, or, Mars and Venus Find Something in Common.

The objective of this paper is to examine the degree of similarity of the persistent CO2 greenhouse found on Venus to that of ancient Mars. The discovery of Jarosite, a mineral formed in the presence of strong sulfuric acid, evokes conditions more associated with Venus, where strong oxidizing conditions and strong sulfuric and hydrochloric acids are observed in its clouds. It is observed that large areas of Mars are both aqueously altered and highly oxidized and that carbonates are not found in any quantity, and that this reflected also in Mars meteorites. This suggests that conditions may have been present on Mars that allowed a stable and persistent greenhouse by the production of a significant oxygen component in the atmosphere with attendant strong mineral acids. Soil compositions of both Venus and Mars established by the Venera and Viking probes both show strong enhancement of both sulfur and chlorine over earth soils, and like Mars, Venus is believed to have supported a paleo-ocean. Two problems confront models of conventional carbon dioxide greenhouses on Mars, one is the long term chemical stability of such an atmosphere against the formation of carbonates, and second is the short term thermodynamic instabilities of a dense carbon dioxide atmosphere to condensation in the presence of insolation, impacts, volcanic eruptions and other cooling events. Venus apparently solved the problem of carbonate formation by having an oxidizing and acid rich atmosphere. An oxygen component, either biogenic or created by photo-disassociation of water, could have created acidic and highly oxidized conditions on Mars that provided chemical stability to a greenhouse by preventing formation of carbonates. Also, the presence of a Northern Paleo-ocean on Mars would have created thermal and gas pressure buffering of the climatic system to stabilize it against minor thermodynamic perturbations. Therefore, Venus demonstrates a persistent greenhouse could have existed on Mars that was both oxygenically and hydrologically stabilized. The persistent greenhouse on mars could have been terminated by a large atmospheric cooling event in the Early Amazonian that froze over the paleo-ocean stabilizing the greenhouse. © 2007 American Institute of Physics [ABSTRACT FROM AUTHOR]