Interstellar 60Fe on the Surface of the Moon

Abstract

A dying massive star ends in a supernova explosion ejecting a large fraction of its mass into the interstellar medium. If this happens nearby, part of the ejecta might end on Solar System bodies and, in fact, radioactive Fe60 has been detected on the Pacific ocean floor in about 2 Ma old layers. Here, we report on the detection of this isotope also in lunar samples, originating presumably from the same event. The concentration of the cosmic ray produced isotope Mn53, measured in the same samples, proves the supernova origin of the Fe60. From the Fe60 concentrations found we deduce a reliable value for the local interstellar fluence in the range of 1×10^8 at/cm2. Thus, we obtain constraints on the recent and nearby supernova(e).