The idea of Mars being host to extraterrestrial life, either currently or long ago in the past, has beguiled scientists for centuries.
The discovery of frozen water on the Red Planet gave scientists hope that life may be able to survive in the frigid world, as all life as we know it requires water to thrive.
However, according to a new commentary in the journal Nature Astrobiology by Dirk Schulze-Makuch, an astrobiologist at the Technische Universität Berlin, Germany, we may actually have killed life lurking on Mars—using water.
“The experiments performed by NASA’s Viking landers may have accidentally killed Martian life by applying too much water,” Schulze-Makuch wrote in the paper.
NASA/JPL-Caltech/MSSS / ISTOCK / GETTY IMAGES PLUS
Is There Life on Mars?
While missions like Viking, Curiosity, and Perseverance have searched for signs of past or present life, including organic molecules and habitable conditions, no conclusive evidence of living organisms has been discovered.
The Viking missions, launched by NASA in 1975, were the first successful attempts to land on Mars and conduct detailed exploration. Viking 1 and Viking 2 each included an orbiter and a lander, which landed on the Red Planet in 1976.
“Viking’s life detection experiments were designed based on culturing methods used in laboratories on Earth. That is, they would provide water and some nutrients to samples, then record any resulting growth, metabolism changes, or reproduction,” Schulze-Makuch wrote.
However, this addition of water during biological experiments on the planet’s surface to detect the presence of life may have killed any microbes lurking in the Martian soil, Schulze-Makuch said.
He said that extremophile microbes (organisms able to live in extreme environments) in the Atacama Desert on Earth have adapted to the intensely arid conditions over millions of years by inhabiting salt crusts, living under translucent rocks, and entering extended dormancy. These organisms, mainly halophiles (thriving in high salt concentrations), are endolithic, extracting moisture from the air using salts. These salts can dissolve, forming brines that support microbial growth.
Paradoxically, excessive water can cause osmotic shock, killing these salt-loving bacteria and archaea. After one rare heavy rainfall in the Atacama, up to 87 percent of microbial species perished as a result of the floods.
“As lessons from the Atacama Desert show, if microbes are adapted to a hyperarid environment, they are likely to be very sensitive to too much water and would only be able to survive the exposure to small amounts of liquid water,” Schulze-Makuch said. “If any indigenous microbial life still exists there, Martian life could be expected to be even more sensitive to the sudden presence of liquid water.”
On even drier Mars, potential microbial life might be highly vulnerable to sudden exposure to liquid water, and therefore, the use of water in the Viking experiments may have killed any microbes in the soil, if there ever were any.
“The Viking experiments were conducted too warm and wet, under the assumption that Martian life would require liquid water as do most life forms on Earth,” Schulze-Makuch said.
However, this would only affect the small number of potential microbes contained within a Martian soil sample, and not other microbes hidden in the Martian soil around the landers. So, landing on Mars doesn’t necessarily mean we are killing off possible extraterrestrial lifeforms.
Schulze-Makuch suggested that in the future, NASA shouldn’t “follow the water” when looking for life beyond Earth, and rather “follow the salts” instead.
Are there other rocks like this near the Jezero Crater rim? I’m on my way to find out.
P.S. – My team has really enjoyed reading your theories about what this “zebra rock” might be! https://t.co/KDYaWhRBeh
— NASA’s Perseverance Mars Rover (@NASAPersevere) September 27, 2024
“We should in addition follow hydrated and hygroscopic [able to absorb moisture from the air] compounds—salts—as a way to locate microbial life. Nearly 50 years after the Viking biology experiments, it is time for another life detection mission—now that we have a much better understanding of the Martian environment,” Schulze-Makuch said.
“Prime exploratory locations to probe for life on Mars would thus be the Eastern Margaritifer Terra in the equatorial region and the Southern Highlands of Mars, where NaCl-dominated salt rocks are abundant.”
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References
Schulze-Makuch, D. (2024). We may be looking for Martian life in the wrong place. Nature Astronomy.
