Evaluating the Habitability of Martian Surface and Subsurface Brines Using Terrestrial Polyextremophiles as Biological Analogs

Present-day Mars presents a hostile environment for life due to extreme cold, low atmospheric pressure, scarce oxygen, intense ultraviolet (UV) radiation, and toxic perchlorate salts. To evaluate the boundaries of Martian habitability, this comparative literature review examines measured Martian environmental conditions alongside the survival limits of three terrestrial polyextremophiles: Planococcus halocryophilus, Deinococcus radiodurans, and Halobacterium salinarum. Data synthesized from peer-reviewed studies (2017–2024) show that while P. halocryophilus grows at -15°C and tolerates up to 12 wt% \(NaClO_{4}\), D. radiodurans survives 140 kGy of ionizing radiation when desiccated and frozen, and H. salinarum thrives in saturated brines using light-driven anaerobic metabolism. However, the lack of biologically accessible liquid water—driven by hyper-concentrated eutectic perchlorate brines (~52.6 wt%) and UVC-activated perchlorate photochemistry—severely restricts active growth on the exposed surface. While deep subsurface aquifers offer the greatest long-term protection, the engineering difficulty of deep drilling means near-term missions should first target shielded surface micro-habitats, such as porous rocks and shallow salt crusts, where novel extremophilic life may persist.