In just over a decade, samples of Martian soil scooped up by the Mars Perseverance rover are set to return to Earth after being retrieved by the first humans to set foot on Mars.
While scientists are excited to see what scientific discoveries await, they may have to temper their expectations. That's because acidic fluids — which once flowed on the surface of the red planet — may have destroyed biological evidence hidden within Mars' iron-rich clays.
A new paper, by researchers at Cornell University and at Spain's Centro de Astrobiología, details how they came to this conclusion.
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In order to come to the conclusion that there has likely been a degradation of biological material on Mars' red clay surface, the researchers carried out simulations involving clay and amino acids.
Their results were published in the paper, "Constraining the Preservation of Organic Compounds in Mars Analog Nontronites After Exposure to Acid and Alkaline Fluids," on September 15th in Nature's Scientific Reports.
"We know that acidic fluids have flowed on the surface of Mars in the past, altering the clays and its capacity to protect organics," Alberto G. Fairén, a corresponding author of the paper, explained in a press release.
Glycine, the 'perfect informer'
The researchers explain that the internal structure of clay is organized into layers, in which we would typically find well-preserved evidence of biological life, such as lipids, nucleic acids, peptides, and other biopolymers.
In the laboratory, the team simulated Martian surface conditions by trying to preserve an amino acid called glycine in a lump of clay that had previously been exposed to acidic fluids.
"We used glycine because it could rapidly degrade under the planet's environmental conditions," Fairén explained. "It's a perfect informer to tell us what was going on inside our experiments."
The difficulty of searching for organic compounds on Mars
The researchers exposed the glycine-infused clay to Mars-like ultraviolet radiation: the results show substantial photodegradation of the glycine molecules embedded in the clay. Essentially, exposure to acidic fluids erased the interlayer space, turning it into gel-like silica.
"When clays are exposed to acidic fluids, the layers collapse, and the organic matter can't be preserved. They are destroyed," Fairén said. "Our results in this paper explain why searching for organic compounds on Mars is so sorely difficult."
NASA's Perseverance rover launched on July 30th and is set to land at Mars' Jezero Crater next February. The rover will collect soil samples from the red planet, which will be collected and sent back to Earth by the 2030s.
While the Perseverance mission is still important for potential future Mars colonists and for our understanding of our solar system, the findings of the new study may prove to be a setback for our ability to detect the presence of any ancient life on Mars.