Physics
Scientific paper
Dec 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002agufm.p51b0351l&link_type=abstract
American Geophysical Union, Fall Meeting 2002, abstract #P51B-0351
Physics
5407 Atmospheres: Evolution, 5415 Erosion And Weathering, 6225 Mars
Scientific paper
The uniformitarian case is made for Mars. Processes active in the current epoch include impacts, volcanism, wind, ice condensation/sublimation, and probable localized liquid water flow in gully forming events. The amount of carbon dioxide available at the surface at the end of heavy bombardment was likely to have amounted to only 50-100 hPa. Because water ice would have been partly protected from impact erosion, as much as several hundred meters of equivalent ocean may have been present, but impacts coupled with atmospheric transport would have moved almost all ice to polar and sub-polar deposits well before the end of heavy bombardment. Most of the carbon dioxide would have been frozen into polar deposits although orbital parameter variations would have caused occasional release and periods of relatively high atmospheric pressure. Surface pressure would never have been high enough to sustain a warm wet climate, but because wind stress is very sensitive to pressure, aeolian surface modification in the Noachian and early Hesperian would often have been far more effective than today. Reservoirs of C, O, and H would subsequently have declined to their present levels as a result of atmospheric escape. During and after heavy bombardment, volcanism, ice deposition, and redistribution of dust by wind and impacts would have produced widespread and deep layering that has been continuously subject to erosion by impacts, sublimation, and wind action. Lava, possibly locally associated with juvenile water and lahars, could have formed large outflow channels in equatorial regions. These would have initially resembled volcanic outflow channels on Venus, but would have been subsequently modified and streamlined by atmospheric deposition and deflation. The origin of valley network features is varied and generally obscure, but volcanic processes, debris flows, and subsequent modification by atmospheric deposition and deflation could account for many of them. As discussed by Segura et al. (2002, this session), brief liquid water flows due to very large early impacts could also have produced some valley network features. This hypothesis is consistent with the low abundances of heavy noble gases, apparent absence of carbonates, paucity of aqueous minerals, immense post-Noachian low latitude outflow channel features, evidence for widespread sedimentation and erosion, and theoretical problems with models calling for an early warm climate. It is argued that it deserves consideration along with hypotheses that entail massive liquid water flows or warm climates in the past.
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