When the Rosalind Franklin rover drills into Martian rock in 2030, it will carry an instrument fine-tuned to detect one of the most subtle signs of ancient life: the molecular fingerprints of chirality. Scientists have now proven that the rover’s Mars Organic Molecule Analyzer (MOMA) can distinguish between mirrored forms of two stable hydrocarbons—pristane and phytane—marking a breakthrough in the search for unambiguous biosignatures on Mars. These molecules, which on Earth are derived from chlorophyll and other biological sources, could persist for billions of years in the harsh Martian environment, making them ideal targets in the hunt for long-dead microbes.
The challenge has always been telling life-made molecules from those formed by chemistry alone. Many organic compounds are chiral, meaning they come in left- and right-handed versions—mirror images that behave identically in most chemical reactions. But life, due to its self-replicating machinery, overwhelmingly produces just one form. On Earth, amino acids in proteins are almost exclusively left-handed; sugars in DNA are right-handed. If life ever arose on Mars, it too would have favored one chiral form over the other. Non-biological processes, in contrast, produce a 50/50 mix. Finding an imbalance—called enantiomeric excess—would be powerful evidence of past biology.
To test MOMA’s ability to detect such an imbalance, researchers led by Guillaume Leseigneur at the Max Planck Institute for Solar System Research used samples from the Murchison meteorite, which fell in Australia in 1969 and contains a rich inventory of extraterrestrial and terrestrial organic molecules. They ran replicas of MOMA’s chiral separation tubes through rigorous laboratory analyses, successfully separating the enantiomers of both pristane (C19H40) and phytane (C20H42) for the first time—despite their extreme chemical inertness. This demonstrates that MOMA, equipped with a gas chromatograph, mass spectrometer, and laser excitation system, has the sensitivity and precision needed for the task.
But the results brought a surprise. The pristane and phytane in the Murchison meteorite showed no chiral bias—equal parts of both mirror forms—ruling out contamination from modern Earth biomass, which would have shown a strong preference. Instead, the team traced the source to atmospheric aerosols from fossil fuel combustion, likely picked up during the meteorite’s fiery descent. This finding, supported by comparisons with oil shales from sedimentary rocks, reveals how deeply human activity has altered even extraterrestrial samples.
The implications are profound. If MOMA can detect chiral imbalances in Martian molecules, it could provide the first definitive proof of ancient life beyond Earth. As the Rosalind Franklin rover prepares for launch, the success of this test sharpens our tools—and our hope—for answering one of humanity’s oldest questions.