Biology
Scientific paper
Dec 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010agufm.p44b..03s&link_type=abstract
American Geophysical Union, Fall Meeting 2010, abstract #P44B-03
Biology
[3610] Mineralogy And Petrology / Geochemical Modeling, [5220] Planetary Sciences: Astrobiology / Hydrothermal Systems And Weathering On Other Planets, [5420] Planetary Sciences: Solid Surface Planets / Impact Phenomena, Cratering
Scientific paper
During the Noachian, Mars - like the other terrestrial planets - was affected by the inner solar system cataclysm resulting in a heavily cratered surface [Kring & Cohen, 2002, JGR 107]. Therefore, impact cratering is an important, if not the dominating geologic process of that era. While the Martian surface during the Noachian is thought to have been a warm and wet place, this has likely changed towards the end of the Noachian. Many of the craters formed during the inner solar system cataclysm, and especially towards its end, therefore may have hit a cold surface hosting a cryosphere of up to 6 km thickness. But craters as small as 12 km in diameter could have penetrated this cryosphere, giving surface access to liquid water and providing warm water environments [Schwenzer et al., in preparation]. In general, impact crater formation in water (or ice) bearing Martian crust triggered long-lasting hydrothermal systems in an aureole under the entire crater diameter [Abramov & Kring, 2005, JGR 110]. This water flow caused mineral reactions, which can be investigated by thermochemical modeling. Taking Martian meteorite chemistry as a proxy, clay minerals such as chlorite and nontronite result from hydrothermal alteration of Martian lherzolithic composition [Schwenzer & Kring, 2009, Geology]. Both, chlorite and nontronite, have been detected in modification zones and central peaks of Martian craters [Ehlmann et al., 2009, JGR 114] providing Martian ground truth for the model observations. Taking the entirety of known Martian rock chemistry, the range spans from dunitic to basaltic. Investigations of soil and surface rocks by rovers on Mars [Gellert et al., 2006, JGR 111] found higher S-content than has been found in the meteorites. With this variety of rock compositions as potential host rocks for hydrothermal activity, the range of alteration silicates includes serpentine, amphibole and a variety of clay minerals and zeolites. The non-silicate alteration products include sulphides, sulphates and various hydroxides and oxides. Interestingly, the most reducing conditions produce gas, mainly methane and H2, during serpentine formation. This process is well known from terrestrial (e.g., mid ocean ridge) environments [e.g., Oze & Sharma, 2005, GRL 32]. If CO2 was present, it could lead to carbonate formation, producing Fe-Mg carbonates under most thermochemical conditions. This in turn, links to the observation of carbonate in the Isidis region of Mars [Ehlmann et al., 2008, Science 322]. The most recent finding of carbonate on Mars by the rover Spirit in Gusev crater, however, is thermochemically linked to the same neutral to alkaline water activity [Morris et al., 2010, Science 329] that is produced by impact-generated hydrothermal systems. Although the link to Gusev crater impact processes has not been established yet, the thermochemical conditions required for carbonate formation were likely present under the crater, in the central uplift and the inner crater rim for more than 300,000 years after Gusev crater formation. Martian craters in their entirety may give insights into the early evolution of planetary crust and potentially habitable niches therein.
Abramov Oleg
Schwenzer Susanne P.
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