NASA’s Mars rovers shouldn’t expect to detect biomarkers on the Red Planet’s surface, according to a new study based on an experiment aboard the International Space Station (ISS) that suggests ultraviolet radiation will break down these molecules after only a year or two.
Both Curiosity and Perseverance use Raman spectrometers to identify organic compounds and, potentially, biological molecules on March‘ surface. A Raman spectrometer uses a laser to excite molecules, and then the way those excited molecules scatter light tells scientists what kind of molecules they are. In particular, they are sensitive to organic compounds, which is why they are a key tool for both rovers.
However, new research in international space station led by Mickael Baqué of the German Aerospace Center (DLR) questioned the usefulness of instruments on Mars. Due to its weak atmosphere and lack of magnetic shielding, Mars is flooded with a torrent of ultraviolet light from the sunwhich can be harmful to biological cells.
Related: 12 stunning photos of the Perseverance rover’s first year on Mars
Baqué’s team exposed a sample of seven different types of biomolecules to Mars-like conditions for 469 days in the Biology and Mars (BIOMEX) experiment, which is installed on the Expose-R2 platform at the exterior of the ISS. Temperature, daily light cycles, and ionizing radiation levels were matched to mimic Mars, and the sample was placed among simulated Mars regoliths.
The biomolecules involved in the experiment were all those commonly found in organisms: 𝛃-carotene (which is an antioxidant and light-reactive pigment), chlorophyllin (derived from the chlorophyll that plants use to treat sunlight), naringenin (a common antioxidant), quercetin (another common antioxidant), melanin (a pigment that protects against ultraviolet rays), cellulose (a component of plant cell walls) and chitin (found in the skeletons of insects).
Ordinarily, Raman spectroscopy can detect these seven biomolecules. However, by the end of the experiment, Baqué’s team found that only three – chlorophyllin, quercetin and melanin – remained detectable, and even their signal had weakened by 30% to 50%. The ultraviolet light the molecules had been exposed to had degraded them to the point that Raman spectroscopy could not recognize them.
Crucially, the technique could still detect biomolecules from a control sample that was shielded from radiation by deeper layers of regolith. These detections imply that Perseverance or future rover missions could still identify biomarkers buried in the surface.
“Ultraviolet [radiation] only penetrates the first few micrometers to millimeters of the Martian surface, so organic compounds and potential biomolecules must be protected beyond those depths,” Baqué told Space.com. (A micrometer is about 1% of the width of a strand of hair; 1 millimeter is smaller than a grain of sand.) Dig a little deeper, and the Martian regolith should provide adequate radiation shielding.
Meanwhile, the European Space Agency Rosalind Franklin ExoMars rover will take a robotic drill to Mars that can dig 6.6 feet (2 meters) into the surface. The launch of this rover was delayed because a Russian lander was supposed to bring it to the surface, and Europe will no longer cooperate with Russia because of his invasion of Ukraine. Even facing a 2028 launch at the earliest, the Rosalind Franklin rover offers our best chance of finding life on Mars since viking missionssay the scientists.
If the Rosalind Franklin rover finds evidence of microbial lifethen these microbes will have evolved in a very hostile environment.
“The Martian surface appears very harmful for organic compounds because of ultraviolet radiation, but also [because of] oxidizing substances and finally – but especially for long-term preservation over billions of years – ionizing radiation,” Baqué said.
Curiously, the results differ from those of similar BIOMEX experiments that exposed intact organisms, living and dead, to similar conditions bathed in ultraviolet radiation. These experiments showed that the body’s biomolecules remain intact. Baqué said he attributes this discrepancy to life’s ability to protect its own cells.
“Just as regolith can protect directly exposed molecules from photodegradation by ultraviolet radiation, other cellular components can perform the same role in organisms,” he said.
The results mean, however, that Raman spectroscopy may play a lesser role in the search for Martian life, partial or present, than scientists expected. Baqué’s team concludes that all biomarkers on the surface would degrade in a few years at most, meaning that unless Mars is teeming with enough life to constantly replenish these biomarkers, the surface will appear dead – which can or not be the real picture.
The research was published Wednesday (September 7) in Scientists progress.
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