Curiosity Rover Collects First Martian Bedrock Sample

Ancient indigenous organic molecules could be also destroyed or transformed by the ionizing radiation in the shallow subsurface of Mars. Due to a thin martian atmosphere and lack of magnetic field, the surface of Mars has been bombarded continuously by the energetic particles of the galactic and solar cosmic rays (GCRs and SCRs) for much of its history. Unlike UV radiation which is absorbed in the first mm of soil (Mancinelli and Klovstad 2000; Cockell et al. 2005), GCRs can penetrate down to 1 meter below the surface (Dartnell et al. 2007). Over the long period of exposure, cosmic rays particles have the capacity to transform complex organic compounds into macromolecules having different, more refractory chemistry and/or into smaller molecules broken from a parent molecule. The latter case may occur either by direct impacts or by secondary reaction with oxidative radicals produced by radiation in the immediate vicinity of the organic molecules (Dartnell et al. 2008). It is not clear how such long-term degradation would affect SAM?s measurements of organic compounds at the ancient geologic outcrops because the rates of erosion are highly variable on Mars (Golombek et al. 2006). Erosion of the ancient rock would naturally expose ?fresh? (less irradiated) material to the surface with potentially ?unbroken? organic molecules. Furthermore, SCRs, which are less energetic than GCRs, cannot penetrate and destroy organic matter deeper than 2 cm below the surface (Pavlov 2011). Therefore, MSL?s drilling and sampling of outcrops from 5 cm below the surface will exclude the effects of degradation of organic matter by solar cosmic rays. Finally, using the radiolysis constants of amino acids Kminek and Bada (2006) and Pavlov (2011) demonstrated that simple organic compounds with masses below 100 amu, should have a good chance to survive long-term exposure to GCRs in the shallow subsurface even extremely low surface erosion rates. Results from Curiosity?s Radiation Assessment Detector (RAD) will provide modern radiation characteristics that will help improve long-term modeling of the surface radiation on Mars and possibly constrain its affects on near surface organic chemistry.

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