Revisiting the cosmic-ray induced Venusian radiation dose in the context of habitability

TL;DR

This study uses advanced modeling to reassess Venusian radiation doses, revealing previous underestimations and suggesting that potential microbial life in the cloud layer would not be significantly harmed by solar events.

Contribution

First comprehensive modeling of altitude-dependent Venusian radiation dose using shape- and composition-specific phantoms, improving hazard estimates for potential cloud-based life.

Findings

Previous models underestimated radiation hazard by up to a factor of five.

Strong solar events would not have posed a significant threat to microorganisms in the habitable zone.

Different detector models influence the estimated radiation dose levels.

Abstract

The Atmospheric Radiation Interaction Simulator (AtRIS) was used to model the altitude-dependent Venusian absorbed dose and the Venusian dose equivalent. For the first time, we modeled the dose rates for different shape-, size-, and composition-mimicking detectors (phantoms): a CO$_2$-based phantom, a water-based microbial cell, and a phantom mimicking human tissue. Based on a new model approach, we give a reliable estimate of the altitude-dependent Venusian radiation dose in water-based microorganisms here for the first time. These microorganisms are representative of known terrestrial life. We also present a detailed analysis of the influence of the strongest ground-level enhancements measured at the Earth's surface, and of the impact of two historic extreme solar events on the Venusian radiation dose. Our study shows that because a phantom based on Venusian air was used, and because furthermore, the quality factors of different radiation types were not taken into account, previous model efforts have underestimated the radiation hazard for any putative Venusian cloud-based life by up to a factor of five. However, because we furthermore show that even the strongest events would not have had a hazardous effect on putative microorganisms within the potentially habitable zone (51 km - 62 km), these differences may play only a minor role.