Assessing the survivability of biomarkers within terrestrial material impacting the lunar surface
Abstract
Organic material and biological markers (biomarkers) are effectively non-existent in the geological record of the Earth before ~3.8 billion years ago. This paper investigates the potential for ejected terrestrial material (i.e., terrestrial meteorites) to survive impact with the lunar surface, modelled using the iSALE hydrocode. Previous modelling 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. However, this paper shows the critical importance of considering both pressure and temperature within the projectile, and the inclusion of both shock and shear heating during simulations. Shear heating provides an additional, underappreciated source of heat within the projectile material at the impact velocities considered for terrestrial meteorites impacting the Moon (i.e., between 2.5 and 5 km/s). Nevertheless, in spite of the higher temperatures, this work shows that biomarkers within terrestrial meteorites are likely to survive after impact with the Moon, especially at the lower end of the range of impact velocities considered. Higher projectile porosity is shown to be detrimental to the survival of biomarkers, whereas a higher target porosity increases the chances of projectile biomarker survival. 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. Cooling timescales are investigated, with radiatively cooling projectile fragments providing the best, long-term conditions for biomarker survival. Subsequent burial would preserve and protect surviving biomarkers from further degradation due to fluctuating surface temperatures and cosmic radiation. Surviving terrestrial material on the Moon has the potential to provide important astrobiological information on a period of Earth's early geological and biological evolution that is no longer retained on Earth itself.
- Publication:
-
43rd COSPAR Scientific Assembly. Held 28 January - 4 February
- Pub Date:
- January 2021
- Bibcode:
- 2021cosp...43E.355H