The Production of Terrestrial Meteorites - Moon Accretion and Lithopanspermia

摘要

The conditions under which terrestrial, impact-derived ejecta can be launched into cis-lunar space is studied. A numerical code is developed in order to follow the ablation and deceleration conditions of material ejected from the Earth's surface and outwards through the atmosphere. The deceleration filtering-effect imposed by Earth's atmosphere results in multi-meter-sized, 5 to 20 meters across, fragments escaping into cis-lunar space being favored. Smaller fragments tend to be more rapidly decelerated than larger ones and are re-accreted by the Earth. The conditions under which Earth-ejected material might impact upon the Moon is additionally considered. It is found that for encounter speeds smaller than some 7 km/s, terrestrial meteorites might be expected to survive upon impact (that is they will not undergo shock melting) when encountering the Moon's regolith. It is argued that terrestrial meteorites may well survive, with identifiable features (fusion crust and mineralogy), for long periods of time within the lunar regolith (a result recently vindicated through the discovery of terrestrial material - launched during the late heavy bombardment - contained within a lunar impact breccia #14321, collected during the Apollo 14 Moon landing mission). Further to this, the important role that terrestrial meteorites must have played in transporting microbial life to other potentially habitable locations within the solar system is discussed.