Last week, NASA landed its Perseverance rover on Mars, kicking off a new mission that will hunt for signs of microbial life that might have thrived in the wetter, warmer conditions on the red planet billions of years ago. Finding tiny Martian fossils would be one of the most spectacular breakthroughs in history. But what about the odds that life could exist on Mars right now?
Answering this question is important not only for understanding modern Mars, but also to mitigate the risk that microbes from Earth are accidentally deposited by spacecraft on this pristine planet, a process known as forward contamination.
To test out the potential resilience of earthly microbes on Mars, scientists launched a box containing four types of bacteria and fungus into the stratosphere on a high-altitude balloon, where the organisms were exposed to several hours of Mars-like conditions including radiation.
The experiment revealed that fungi species, such as black mold, “may be resistant to the Martian surface if inadvertently delivered by spacecraft missions,” according to a study published on Monday in the journal Frontiers in Microbiology.
Though many other studies have previously concluded that Earth life could survive for short periods on Mars, this research provides a rare example of an experiment that simultaneously tested organisms under multiple simulated Martian conditions, such as pressure, atmospheric properties, and radiation exposure.
“Whether terrestrial life can withstand the Martian environment is of paramount interest for planetary protection measures and space exploration,” reports the study, which was co-led by Marta Filipa Cortesão, Katharina Siems, and Ralf Moeller of the German Aerospace Center (DLR).
“To understand microbial survival potential in Mars-like conditions, several fungal and bacterial samples were launched in September 2019 on a large NASA scientific balloon flight to the middle stratosphere (∼38 km altitude) where radiation levels resembled values at the equatorial Mars surface,” the team explained.
The microbes spent seven hours at that high altitude inside a 40-pound container called the Microbes in Atmosphere for Radiation, Survival, and Biological Outcomes Experiment (MARSBOx). The box was separated into two sample layers; one was exposed to Martian surface radiation levels, which are about 1,000 times more intense than what we experience on Earth, while the other was protected from this radiative onslaught.
This way, the team could isolate the effects of radiation on the microbes from other factors in the experiment, such as temperature fluctuations, pressure, and atmospheric simulations.
While some of the selected microbes died during the flight, the black mold fungus Aspergillus niger proved to be extremely durable under the punishing conditions. Spores of the fungus were successfully revived upon their return to Earth, suggesting that this family of lifeforms “might be considered some of the most likely forward contaminants to survive if inadvertently delivered to Mars,” according to the study.
The possibility that black mold, or a microbe similar to it, could persist on the surface of Mars has major consequences for our exploration of the red planet, especially with regard to human missions.
Unlike robotic rovers, humans can’t be deep-cleaned in sterilization chambers in order to remove microbes from our bodies. If and when humans start exploring Mars in person, mission planners will have to devise strategies to limit the risk of the organisms in our microbiomes spreading to the Martian environment, which would potentially make it difficult to distinguish between terrestrial and alien life.
“Our results underscore the importance of including fungal spores in Mars forward contamination studies and relevant planetary protection policies,” the team concluded.