Assessment of the probability of microbial contamination for sample return from Martian moons I: Departure of microbes from Martian surface

TL;DR

This study assesses the likelihood of microbial contamination from Mars ejecta reaching Martian moons, considering impact survival, atmospheric deceleration, and microbial density estimates, to inform planetary protection protocols.

Contribution

First comprehensive analysis combining impact physics, atmospheric entry dynamics, and microbial density estimation for Martian ejecta potentially contaminating moons.

Findings

Ejecta smaller than 0.03 m rarely reach Phobos due to deceleration and heating.

Microbial survival during impact is significantly affected by impact conditions.

Baseline microbial density in ejecta has been estimated for future contamination risk assessment.

Abstract

Potential microbial contamination of Martian moons, Phobos and Deimos, which can be brought about by transportation of Mars ejecta produced by meteoroid impacts on the Martian surface, has been comprehensively assessed in a statistical approach, based on the most probable history of recent major gigantic meteoroid collisions on the Martian surface. This article is the first part of our study to assess potential microbial density in Mars ejecta departing from the Martian atmosphere, as a source of the second part where statistical analysis of microbial contamination probability is conducted. Potential microbial density on the Martian surface as the source of microorganisms was estimated by analogy to the terrestrial areas having the similar arid and cold environments, from which a probabilistic function was deduced as the asymptotic limit. Microbial survival rate during hypervelocity meteoroid collisions was estimated by numerical analysis of impact phenomena with and without taking internal friction and plastic deformation of the colliding meteoroid and the target ground into consideration. Trajectory calculations of departing ejecta through the Martian atmosphere were conducted with taking account of aerodynamic deceleration and heating by the aid of computational fluid dynamic analysis. It is found that Mars ejecta smaller than 0.03 m in diameter hardly reach the Phobos orbit due to aerodynamic deceleration, or mostly sterilized due to significant aerodynamic heating even though they can reach the Phobos orbit and beyond. Finally, the baseline dataset of microbial density in Mars ejecta departing for Martian moons has been presented for the second part of our study.