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While the search for extraterrestrial life has sparked countless theories, the evidence for past Martian life appears increasingly compelling. Features such as ancient river channels, evidence of seasonal water flows, and isotopic signatures in Martian meteorites all point to a once wet and potentially habitable environment. Yet today Mars is barren, and the fate of any life it once supported remains a mystery—until now, according to a provocative 2024 commentary in Nature Astronomy.
Astrobiologist Dirk Schulze‑Makuch of the Technical University of Berlin argues that we may have already found life on Mars, but that a NASA experiment inadvertently destroyed the sole sample we ever obtained. He focuses on the Viking mission of the 1970s, the only time humans have directly tested another planet for life. Viking’s instruments initially detected trace organic compounds, but subsequent analyses concluded the signals were contaminants from Earth. Schulze‑Makuch suggests this conclusion may have been premature.
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The Viking landers were equipped with a gas chromatograph‑mass spectrometer (GCMS) to analyze Martian regolith for organic molecules. Early GCMS readings revealed chlorinated organics—an unexpected finding since chlorine is rare in terrestrial organic chemistry. NASA therefore attributed the signal to contamination brought aboard the lander. However, similar chlorinated compounds were later detected by the 2008 Phoenix lander and by other rovers, confirming that chlorine‑bearing organics are indigenous to Mars. This raises the possibility that the Viking samples contained genuine Martian organics, potentially produced by microbes.
Schulze‑Makuch proposes two mechanisms by which the Viking GCMS could have eliminated any extant microbes. First, the GCMS heated the soil to several hundred degrees Celsius, a process that would sterilize most microorganisms. Second, other Viking experiments mixed soil with water, an action that could have drowned any microbes adapted to Martian conditions—especially if they resemble the extremophiles we find in Earth’s deserts that thrive without free water. In both scenarios, NASA’s assumption that life requires water may have been overly simplistic, leading to the accidental destruction of the only lifeforms found on Mars.
