How Long Could Earth Microbes Survive on Mars? New Model Offers Insights

Canada - Ekhbary News Agency

Mars Microbial Survival Model: A New Assessment of Forward Contamination Risks in Red Planet Exploration

The quest for past or present life on Mars serves as the singular driving force behind every mission dispatched to the Red Planet, encompassing orbiters, landers, and rovers. However, a persistent concern within the scientific community revolves around the possibility of Earth-based microbes hitching a ride on Mars-bound spacecraft, a phenomenon termed "forward contamination." This concern stems from the potential to mistakenly identify terrestrial microbes as Martian life or for these Earth microbes to influence samples of potential Martian life that might be discovered. While NASA is deeply committed to mitigating these risks to the greatest extent possible, the crucial question remains: can new methodologies help determine the longevity of Earth-based microbial survival on Mars, thereby alleviating anxieties surrounding forward contamination?

Addressing this critical challenge, a team of researchers, spearheaded by York University in Canada, has introduced the Mars Microbial Survival (MMS) model. This innovative model, as noted by the researchers, can be instrumental in estimating the extent of forward contamination originating from Earth-based microbes on Mars. More specifically, the model aims to quantify how long, in Martian sols, terrestrial microbes that evade pre-launch sterilization protocols could potentially survive on the Red Planet post-arrival. For context, a Martian sol, equivalent to a Martian day, is slightly longer than an Earth day, measuring 24 hours and 39 minutes. These significant findings were recently published in a study in *The Planetary Science Journal*.

To achieve this, the research team meticulously analyzed the sterilization processes a spacecraft would undergo during both the cruise phase (en route to Mars) and the surface phase (upon landing). During the cruise phase, spacecraft are subjected to bombardment by solar wind, particularly in the form of Ultraviolet-C (UVC) radiation. Consequently, the team investigated how spacecraft would respond within a vacuum environment under varying temperatures and solar radiation levels. For the surface phase, the model considers the spacecraft's exposure to Martian surface temperatures and pressures. Crucially, it also accounts for the direct incoming solar radiation, a factor amplified by Mars' lack of a protective ozone layer or a robust magnetic field, unlike Earth.

The study involved an analysis of 14 previously utilized landing or crash sites on Mars from past missions, including iconic names like Viking, Pathfinder, Spirit, Opportunity, Curiosity, and Perseverance. The objective was to ascertain the level of sterilization that future spacecraft might encounter across these diverse Martian terrains. The MMS model's findings indicate that while the exteriors of spacecraft are likely sterilized by solar wind, encased rovers or landers benefit from protection against direct solar wind exposure. Nevertheless, these enclosed systems remain susceptible to sterilization from the vacuum environment and significant temperature fluctuations inherent to the Martian setting.

Regarding the surface phase, the MMS model determined that upward-facing spacecraft surfaces could become sterilized within approximately one Martian sol. For the entire spacecraft to achieve sterilization, the model estimates it would take approximately one Martian year (equivalent to 687 Earth days). The MMS model also factored in other significant biocidal elements present on Mars, such as toxic regolith (Martian soil), low surface pressure, and the pervasive lack of moisture (desiccation), all contributing to further sterilization. Intriguingly, the model estimated that it would take around 100 sols for the spacecraft's interior to sterilize due to the heat generated by its components. However, the researchers caution that sterilizing unheated internal components could take considerably longer, potentially up to 25 Martian years.

The study's conclusion offers a nuanced perspective: "The MMS model predicts very low survival rates for bioburdens on both cruise-phase aeroshells and landed spacecraft at each of the 14 landing sites examined. All external spacecraft surfaces were likely sterilized by UVC alone, with small contributions from other biocidal factors. The bioburdens on the internal surfaces of spacecraft will mostly likely be reduced by temperature and low-pressure effects acting synergistically, although it might take up to 25 yr for sterility when considering low pressure alone. While maintaining high planetary protection standards is crucial for successful Mars science missions, we estimate that small numbers of microorganisms on cold internal surfaces of spacecraft might persist for several decades on Mars."

NASA's planetary protection program, formally known as the Jet Propulsion Laboratory (JPL) Biotechnology and Planetary Protection Group (BPPG), maintains a primary objective: to prevent forward contamination by ensuring maximum spacecraft sterilization prior to launch. In line with all scientific endeavors, the BPPG continuously seeks improvement, actively researching and developing enhanced sterilization procedures, including more efficient and cost-effective technologies. The long-term impact of the Mars Microbial Survival model on planetary protection in the coming years and decades remains to be seen, but its contribution to our scientific understanding is undeniable. This is the essence of scientific exploration!

Ekhbary News Agency