An Investigation into Seeding the Solar System Via Terrestrial Meteorites

Abstract

An investigation into whether terrestrial meteorites could seed the solar system is the main purpose of this thesis. An estimate for the minimum amount of terrestrial material that finds its way into interplanetary space over the past 550 million years is made. From the characteristics of known terrestrial impact craters, it is found that at least 1013 kg of material, potentially containing microorganisms, has been ejected from the Earth’s surface into the inner solar system. This estimate is derived upon a reverseengineering approach which links the observed crater diameter to impactor size and then through a set of analytic equations to obtain an estimate of the mass fraction of material ejected, with a speed greater than the Earth’s escape velocity, during the crater-forming process. It is found that some, 67% of the ejected material, is attributed to the formation of the Chicxulub, the largest known crater produced within the Phanerozoic eon. The conditions under which terrestrial, impact-derived ejecta can be launched into cis-lunar and Martian space is also determined. A numerical code was developed in order to follow the ablation and deceleration conditions that the ejected material undergoes as it is ejected from Earth’s surface and travels outwards through the atmosphere. The deceleration caused from Earth’s atmosphere results in a filtering effect with multi-meter sized fragments, some 5 to 20 meters across, being favored in escaping from the planet. Smaller fragments tend to be rapidly decelerated more than larger ones and are re-accreted by the Earth. The larger fragments being in favor of escaping assists in terrestrial meteorites seeding the solar system, as they can shield potential microbes within them from the extreme temperatures, desiccation, and UV radiation found in space. It was determined that a typical asteroid / short-period comet encounter speed of 25 to 28 km/s could produce a terrestrial crater capable of producing ejecta that could, in principle, find its way into orbits that intercept the Moon as well as those of the planets from Mercury out to Jupiter. The conditions under which Earth-ejected material might impact upon the Moon and Mars is also considered. It was found that for encounter speeds smaller than 9 km/s terrestrial meteorites could potentially survive impact, that is they did not undergo shock melting, with the lunar surface. For a Martian impact encounter speeds smaller than 6 km/s would allow for terrestrial meteorites to possibly survive. It is argued that terrestrial meteorites may well survive, with identifiable features such as fusion crust and mineralogy, for long periods of time within the lunar regolith and Martian surface to hopefully be discovered in the future. For the lunar case, a result recently vindicated it through the discovery of terrestrial material, launched during the late heavy bombardment, that was contained within a lunar impact breccia #14321 collected during the Apollo 14 Moon landing mission.