Terrestrial Effects of Nearby Supernovae: Updated Modeling

TL;DR

This study reevaluates the impact of nearby supernovae on Earth by incorporating early-time suppression of cosmic rays, leading to revised estimates of atmospheric and biospheric effects, and suggests the lethal distance is closer than previously thought.

Contribution

The paper introduces an updated model of cosmic ray transport from supernovae, including early-time suppression, which refines estimates of their atmospheric and biological impacts.

Findings

Lower atmospheric ionization and ozone depletion at 100 pc compared to previous models.

Sea-level muon radiation doses are significantly smaller, especially at 50 pc.

The lethal supernova distance is revised to approximately 20 pc, closer than the traditionally assumed 8-10 pc.

Abstract

We have reevaluated recent studies of the effects on Earth by cosmic rays (CRs) from nearby supernovae (SNe) at 100 and 50 pc, in the diffusive transport CR case, here including an early-time suppression at lower CR energies neglected in the previous works. Inclusion of this suppression leads to lower overall CR fluxes at early times, lower atmospheric ionization, smaller resulting ozone depletion, and lower sea-level muon radiation doses. Differences in the atmospheric impacts are most pronounced for the 100 pc case with less significant differences in the 50 pc case. We find a greater discrepancy in the modeled sea-level muon radiation dose, with significantly smaller dose values in the 50 pc case; our results indicate it is unlikely that muon radiation is a significant threat to the biosphere for SNe beyond 20 pc, for the diffusive transport case. We have also performed new modeling of the effects of SN CRs at 20 and 10 pc. Overall, our results indicate that, considering only the effects of CRs, the "lethal" SN distance should be closer to 20 pc rather than the typically quoted 8-10 pc. Recent work on extended SN X-ray emission indicates significant effects out to 50 pc and therefore the case is now strong for increasing the standard SN lethal distance to at least 20 pc. This has implications for studies of the history of life on Earth as well as considerations of habitability in the Galaxy.