Assessing the survivability of biomarkers within terrestrial material impacting the lunar surface

1Samuel H.Halim,1Ian A.Crawford,2Gareth S.Collins,3Katherine H.Joy,2Thomas M.Davison
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2020.114026]
1Department of Earth and Planetary Sciences, Birkbeck, University of London, Malet St., London WC1E 7HX, UK
2Department of Earth Science & Engineering, Imperial College London, Kensington, London SW7 2AZ, UK
3Department of Earth and Environmental Sciences, University of Manchester, Oxford Rd., Manchester M13 9PL, UK
Copyright Elsevier

The history of organic and biological markers (biomarkers) on the Earth is effectively non-existent in the geological record >3.8 Ga ago. Here, we investigate the potential for terrestrial material (i.e., terrestrial meteorites) to be transferred to the Moon by a large impact on Earth and subsequently survive impact with the lunar surface, using the iSALE shock physics code. Three-dimensional impact simulations show that a typical basin-forming impact on Earth can eject solid fragments equivalent to ~10−3 of an impactor mass at speeds sufficient to transfer from Earth to the Moon. Previous modelling of meteorite survivability has relied heavily upon the assumption that peak-shock pressures can be used as a proxy for gauging survival of projectiles and their possible biomarker constituents. Here, we show the importance of considering both pressure and temperature within the projectile, and the inclusion of both shock and shear heating, in assessing biomarker survival. Assuming that they survive launch from Earth, we show that some biomarker molecules within terrestrial meteorites are likely to survive impact with the Moon, especially at the lower end of the range of typical impact velocities for terrestrial meteorites (2.5 km s−1). The survival of larger biomarkers (e.g., microfossils) is also assessed, and we find limited, but significant, survival for low impact velocity and high target porosity scenarios. Thermal degradation of biomarkers shortly after impact depends heavily upon where the projectile material lands, whether it is buried or remains on the surface, and the related cooling timescales. Comparing sandstone and limestone projectiles shows similar temperature and pressure profiles for the same impact velocities, with limestone providing slightly more favourable conditions for biomarker survival.

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