InterstellarFe60on 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 ^{60}Fe 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 ^{53}Mn, measured in the same samples, proves the supernova origin of the ^{60}Fe. From the ^{60}Fe concentrations found we deduce a reliable value for the local interstellar fluence in the range of 1×10^{8} at/cm^{2}. Thus, we obtain constraints on the recent and nearby supernova(e).

Activity measurement of Fe60 through the decay of Co60m and confirmation of its half-life

“…Similar signatures have been found in lunar samples [6] and in microfossil records [7]. These excesses would seem to indicate that the Solar System passed through the debris field of multiple supernova events in the last 10 million years, as discussed in [8].…”

RADIOACTIVE IRON RAIN: TRANSPORTING60Fe IN SUPERNOVA DUST TO THE OCEAN FLOOR

“…Fitoussi et al noted several reasons for the discrepancy, including variations in the background and differences in the uptake efficiencies between the Fe-Mn crust and sediment. An excess of Fe 60 has also been found in lunar regolith samples (Cook et al 2009;Fimiani et al 2012Fimiani et al , 2014Fimiani et al , 2016, but, due to the nature of the regolith, only the presence of a signal is detectable, not the precise arrival time or fluence (Feige et al 2013). Subsequently, results from Eltanin sediment samples from the southern Indian Ocean were reported in Feige (2014), confirming the Knie et al (2004) Fe-Mn crust detection in these sea sediment samples and leading to an estimated arrival fluence of  = Feigé -1.42 10 atoms cm 7 2 .…”

“…Figure 5 collected during the Apollo Moon landings. The measurements cover a range of depths, but an impactor will only penetrate to a depth on order with its diameter ( m m for our SN grains), so we compare only the fluences of the shallowest samples (this will allow for some minor gardening as noted by Fimiani et al 2016, and references therein). We calculated fluences as outlined in Section 3.2, adjusted for 10% cosmogenic (i.e., cosmic ray-produced) Fe 60 , and plotted the results against the expected Sco-Cen and Tuc-Hor relative fluences in Figure 5(c).…”

The Moon as a Recorder of NearbySupernovae

“…On the other hand, both the continual 'gardening' of the surface regolith by meteorite impacts, and possible meteoritic contamination itself, need to be allowed for. Cook et al (2009) and Fimiani et al (2012Fimiani et al ( , 2014Fimiani et al ( , 2016 were able to allow for both the latter effects and have successfully identified 60 Fe enhancements in a number of Apollo samples which are consistent with the accretion of SN ejecta ~2 Myr ago. Although the 60 Fe concentration reported for these lunar samples is about an order of magnitude less than would be expected from the 60 Fe fluence estimates of Fitoussi et al (2008) based on their interpretation of the terrestrial measurements, a number of plausible explanations for the discrepancy have been identified (Cook et al, 2009;Fry et al, 2015;Fimiani et al 2016).…”