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

Abstract

Several searches have found evidence of Fe 60 deposition, presumably from a near-Earth supernova (SN), with concentrations that vary in different locations on Earth. This paper examines various influences on the path of interstellar dust carrying Fe 60 from an SN through the heliosphere, with the aim of estimating the final global distribution on the ocean floor. We study the influences of magnetic fields, angle of arrival, wind, and ocean cycling of SN material on the concentrations at different locations. We find that the passage of SN material through the mesosphere/lower thermosphere has the greatest influence on the final global distribution, with ocean cycling causing lesser alteration as the SN material sinks to the ocean floor. SN distance estimates in previous works that assumed a uniform distribution are a good approximation. Including the effects on surface distributions, we estimate a distance of -+ 46 610 pc for an -SN progenitor. This is consistent with an SN occurring within the Tuc-Hor stellar group ∼2.8 Myr ago, with SN material arriving on Earth ∼2.2 Myr ago. We note that the SN dust retains directional information to within 1• through its arrival in the inner solar system, so that SN debris deposition on inert bodies such as the Moon will be anisotropic, and thus could in principle be used to infer directional information. In particular, we predict that existing lunar samples should show measurable Fe 60 differences.

Numerical studies on the link between radioisotopic signatures on Earth and the formation of the Local Bubble

“…For the remaining steps we took the fall-out on Earth to be isotropic, which was demonstrated by Fry et al (2016) …”

Terrestrial effects of moderately nearby supernovae

“…Recent interest is based on new isotopic evidence, a very broad field (pioneered by Fields and collaborators) which cannot be covered here. For a more complete and timely discussion of possible isotopic evidence, see Fry et al (2016); see also Ludwig et al 2016. At the present time there exists strong evidence for at least two events: late Miocene (7-8 Ma) and most significantly near the Pliocene-Pleistocene boundary (~2.5 Ma; Melott 2016).…”

“…One is being blasted by (potentially radioactive) dust. This is likely to be a hazard only in the case of the infrequent very close events, but is the basis for recent detections at low levels which have confirmed one set of events (Ellis et al 1996;Fry et al 2016).…”

Muon Radiation Dose and Marine Megafaunal Extinction at the end-Pliocene Supernova

“…The work here is a follow-on to a recent fairly comprehensive study [16] modeling the best available information on the event indicated by recent data [1][2][3][4][5][6][7][8][9][10]. We will summarize the assumptions, methods, and results here, but the reader is referred to the original publication [16] for detailed information.…”

“…There is now considerable confirmatory evidence from multiple sources for a supernova (SN) or series thereof over the last ~8 My [1][2][3][4][5][6][7][8][9][10]. The strongest signal is of an event about 2.5 Ma, which coincides within the uncertainties to the Pliocene-Pleistocene boundary at which there was elevated extinction (hereafter PP), qualifying as a mass extinction by at least one set of criteria [11].…”