How can life persist on a planet where liquid water is effectively nonexistent? On the surface of Mars, the combination of freezing temperatures and extremely low atmospheric pressure creates a hostile environment where water would either freeze instantly or evaporate. This has presented a significant challenge to the search for extraterrestrial biology, based on the premise that water is the essential solvent for all known life.
A research team from TU Berlin, led by Prof. Dr. Dirk Schulze-Makuch, has investigated a chemical loophole to this problem: deliquescence. This process occurs when certain salts absorb moisture directly from the air to form concentrated liquid solutions. Because salt significantly lowers the freezing point of water, these resulting brine puddles—known as soles—could theoretically remain liquid even in the extreme cold of the Red Planet.
The chemistry of Martian brine puddles
The formation of these liquid pockets is a theoretical possibility supported by existing data. Scientists have already identified the presence of chlorides, chlorates, and perchlorates on Mars. Each of these substances possesses the ability to trigger deliquescence, which could potentially allow for the formation of liquid solutions on an otherwise dry landscape.
To test if such environments could actually sustain life, the Berlin team used the yeast Debaryomyces hansenii as a biological model. This specific fungus was selected because it is an expert at surviving in high-salinity environments, as it is commonly found on Earth in salt lakes, marine settings, and fermented foods. The researchers viewed this organism as an ideal model for testing resilience in the types of salty conditions found on the Martian surface.
Simulating the Martian surface
The researchers recreated Martian conditions in a laboratory setting, simulating everything from the composition of the soil to the specific salts present and the way water is absorbed from the atmosphere. To mirror the reality of the Martian surface, all samples were first completely dried out.
Once the samples were desiccated, the team introduced them to a moist environment. This allowed the salts to pull water from the air and form the aforementioned soles. The team then monitored the samples over a period of 63 days to determine if any of the yeast cells had survived the initial drying phase and could thrive once the liquid brine returned.
The results, as reported by merkur.de, varied significantly depending on the type of salt involved. In samples containing sodium chloride and sodium chlorate—as well as in a control sample containing no additional salts—the yeast survived the desiccation process.
The toxicity of perchlorates
While some salts acted as a lifeline, others proved lethal. The study found that viability differed greatly when comparing different Martian salts. Shivani Nundoo, the study’s first author, reported that once liquid salt solutions of sodium chloride or sodium chlorate had formed, the yeast did not just survive—it began to multiply.
However, the outcome was entirely different for samples containing sodium perchlorate. In these instances, the researchers found no surviving yeast cells. Despite the perchlorate’s ability to create liquid brine through deliquescence, the chemical composition of the salt itself was too toxic for the Debaryomyces hansenii model to withstand.
This distinction highlights a critical nuance in the search for Martian life. The presence of liquid water—even in the form of brine—is not a guarantee of habitability. The specific chemistry of the salt determines whether a brine puddle is a sanctuary for microbial life or a chemical wasteland.
The findings indicate that the ability of salt-tolerant microbes to recover and grow after total dehydration suggests that life could potentially cycle through periods of dormancy and activity. This cycle would be triggered by the transient appearance of deliquescent brines, meaning the overall habitability of the planet is closely linked to the specific types of minerals present in a given area.
