Possible transfer of lunar matter to Earth due to a nearby supernova

Abstract

Theories of supernova explosion (SNEs)^1–3 as well as correlation of NO⁻₃ in Antarctic ice cores with the dates of historical supernovae⁴, suggest that many Type I SNE may yield an intense 10⁵⁰ erg emission of γ rays. Such a SNE may be expected to occur within a few tens of light years of our Solar System once every hundred million years or so^5,6. A short γ-ray pulse of this magnitude would not only directly affect the terrestrial atmosphere in ways that can be important for surface life⁵, but also be absorbed by the lunar surface. Depending on the γ-ray energies involved, the upper centimetre of lunar surface soil can be evaporated by heating or ejected by the emergence at the surface of a rising pressure pulse. Such expelled lunar soil, moving at speeds near the 2 × 10⁵ cm s⁻¹ lunar escape velocity, could be captured by the Earth's gravitational field and gradually settle through the atmosphere to the Earth's surface. Geological strata for that epoch might then be expected to show an overabundance of iridium (but probably less than that found by Alvarez et al.⁷ in 65-Myr-old sedimentary layers at Gubbio). This would occur since the expelled lunar surface soil should be characterised by an Ir abundance greatly enriched, relative to terrestrial of lunar rocks, by micrometeorite bombardment.