# Ionizing radiation resilience: how metabolically active lichens endure exposure to the simulated Mars atmosphere

## TL;DR

This study shows that some lichens can survive simulated Mars conditions, including X-ray exposure, due to their active metabolism and protective features.

## Contribution

The first demonstration of active metabolism in lichens under simulated Mars conditions with X-ray exposure.

## Key findings

- Diploschistes muscorum showed active metabolism and effective defense mechanisms under Mars-like conditions.
- C. aculeata experienced unbalanced oxidative stress, suggesting no radioprotective role of melanin in this species.
- The heavy crystalline deposit on D. muscorum may enhance resistance to extreme conditions like those on Mars.

## Abstract

To deepen our understanding of lichen adaptation and their potential to colonize extraterrestrial environments, we aimed to identify physiological/biochemical responses of selected lichen species in a metabolically active state to simulated Mars-like conditions in the dark including exposure to X-rays. Our study is the first to demonstrate that the metabolism of the fungal partner in lichen symbiosis was active while being in a Mars-like environment. Diploschistesmuscorum was able to activate defense mechanisms effectively. In contrast, increased oxidative stress and associated damage were not effectively balanced in C.aculeata, which does not support the melanin’s radioprotective function in this species. The heavy crystalline deposit on D.muscorum thallus might offer protection enhancing lichen resistance to extreme conditions. We concluded that metabolically active D.muscorum can withstand the X-ray dose expected on the Mars surface over one year of strong solar activity. Consequently, X-rays associated with solar flares and SEPs reaching Mars should not affect the potential habitability of lichens on this planet.