A supernova at 50 pc: Effects on the Earth's atmosphere and biota

TL;DR

This study models the atmospheric and biological impacts of a supernova occurring at 50 parsecs from Earth, highlighting increased cosmic rays, ionization, and radiation, with effects varying based on magnetic field orientation.

Contribution

It provides detailed modeling of supernova effects at 50 pc, updating previous estimates and exploring magnetic field influence on cosmic ray flux and terrestrial impact.

Findings

Cosmic ray flux increases by a factor of a few hundred in a disordered magnetic field.

Muon radiation on organisms increases by a factor of 150, returning to normal within 10,000 years.

Magnetic field orientation significantly affects cosmic ray flux and potential terrestrial effects.

Abstract

Recent 60Fe results have suggested that the estimated distances of supernovae in the last few million years should be reduced from 100 pc to 50 pc. Two events or series of events are suggested, one about 2.7 million years to 1.7 million years ago, and another may at 6.5 to 8.7 million years ago. We ask what effects such supernovae are expected to have on the terrestrial atmosphere and biota. Assuming that the Local Bubble was formed before the event being considered, and that the supernova and the Earth were both inside a weak, disordered magnetic field at that time, TeV-PeV cosmic rays at Earth will increase by a factor of a few hundred. Tropospheric ionization will increase proportionately, and the overall muon radiation load on terrestrial organisms will increase by a factor of 150. All return to pre-burst levels within 10kyr. In the case of an ordered magnetic field, effects depend strongly on the field orientation. The upper bound in this case is with a largely coherent field aligned along the line of sight to the supernova, in which case TeV-PeV cosmic ray flux increases are 10^4; in the case of a transverse field they are below current levels. We suggest a substantial increase in the extended effects of supernovae on Earth and in the lethal distance estimate; more work is needed.This paper is an explicit followup to Thomas et al. (2016). We also here provide more detail on the computational procedures used in both works.