Today, Mars is a cold and dry desert planet. Billions of years ago, it likely offered significantly more life-friendly conditions.
© ESA & MPS for OSIRIS Team MPS/UPD/LAM/IAA/RSSD/INTA/UPM/DASP/IDA
The search for extraterrestrial life is shifting from the discovery of organic molecules to the rigorous verification of their origin. While previous missions have identified organic compounds on Mars, the critical challenge remains distinguishing biological signatures from abiotic chemical reactions under conditions that are poorly replicated on Earth. The European Space Agency’s (ESA) ExoMars program is addressing this gap with the Rosalind Franklin rover, scheduled for a 2030 deployment to the Oxia Planum region, a clay-rich ancient delta chosen to maximize the chances of preserving traces of past life.
Unlike previous strategies that relied heavily on returning samples to Earth-a process currently hampered by funding constraints, geopolitical frictions and the technical risk profile of Mars Sample Return-the Rosalind Franklin mission emphasizes high-fidelity in-situ analysis. This approach reduces the dependency on terrestrial laboratories, mitigates the risks associated with sample transport and quarantine, and gives mission planners more freedom within existing planetary protection rules.
The Architecture of Molecular Detection
Central to the rover’s capability is the Mars Organic Molecule Analyser (MOMA). This instrument is not a single sensor but a complex integrated system designed to identify volatile components in Martian soil and rock and, crucially, to characterize their structure in enough detail to test whether biology is the most plausible explanation. To confirm the possible presence of life, MOMA focuses on specific hydrocarbons-pristane and phytane-which are highly stable and often serve as biomarkers on Earth because they can persist long after the organisms that produced them have disappeared.
| MOMA System Component | Technical Function |
|---|---|
| Gas Chromatograph | Separates complex gas mixtures into individual chemical components, allowing targeted analysis of specific molecules. |
| Mass Spectrometer | Determines the molecular mass and structure of the separated components, building a chemical fingerprint for each species detected. |
| Pyrolysis Furnaces | Heats rock and soil samples to release bound volatile organic compounds without the need for liquid reagents. |
| Excitation Laser | Provides additional spectroscopic analysis of the sample, enabling complementary detection pathways for fragile organics. |
| Coated Capillary Tubes | Enables the separation of chiral molecules based on their interaction with the coating, resolving mirror-image forms. |
Starting in 2030, the ESA rover Rosalind Franklin is set to search for traces of life on Mars.
© ESA/ATG medialab
Decoding Biosignatures through Chirality
The technical cornerstone of the MOMA instrument is its ability to detect chirality. Many organic molecules exist as enantiomers-mirror images of one another that are not superimposable. In biological systems, life almost exclusively utilizes one specific mirror configuration. A finding of “homochirality” (a dominance of one version) in a well-characterized geological context would be a powerful indicator of biological processes rather than random chemistry.
“Chirality is a valuable tool in the search for past extraterrestrial life,” explains co-author Uwe Meierhenrich of Côte d’Azur University. Conversely, abiotic processes typically produce a racemic mixture, where both mirror forms exist in equal proportions, diluting any asymmetry that life might otherwise imprint.
The stability of these molecules is vital for deep-time exploration, where any original biosignature may have been exposed to billions of years of radiation and oxidation. As MPS scientist Guillaume Leseigneur notes, “If life once existed on Mars, then molecules like pristane and phytane represent important molecular biosignatures that could have survived to this day.” For mission designers and funding agencies, that persistence is what justifies building a rover around the capability to tell subtle chemical patterns apart.
Atmospheric Interference and the Murchison Study
To validate the instrument’s sensitivity before launch decisions are locked in, researchers conducted a stress test using the Murchison meteorite. This carbonaceous chondrite serves as a proxy for Martian material due to its organic richness and its history as one of the most intensely studied meteorites on Earth. The goal was to determine if MOMA could successfully separate the chiral variants of pristane and phytane under realistic, complex conditions.
“Chiral separation of pristane and phytane requires high instrument sensitivity and measurement accuracy, both of which we show MOMA can achieve,” says MOMA team member Fatma Yesil Sahan. Demonstrating that performance on a heritage sample is a prerequisite for committing public money to fly the system hundreds of millions of kilometres away.
The Murchison meteorite fell in Australia in 1969, breaking into numerous fragments. It belongs to the carbonaceous chondrite group of meteorites. These meteorites are considered to be particularly pristine.
© MPS / T. Klawunn
The results revealed a surprising contamination pattern. Rather than showing biological asymmetry, the meteorite contained equal proportions of all chiral variants. This suggests the meteorite absorbed aerosols from fossil fuel combustion while plunging through Earth’s atmosphere and during subsequent decades of curation on Earth.
This finding was supported by comparing the samples to oil shales. As co-author Manuel Reinhardt explains, “Petroleum forms in these rocks over millions of years at great depths under the influence of heat and pressure.” These conditions destroy chiral imbalance, mirroring the results found in the Murchison sample and underscoring how easily planetary materials can acquire misleading terrestrial signatures.
Planetary Protection and Mission Strategy
The discovery of terrestrial contamination in the Murchison meteorite highlights a critical challenge in planetary protection. To avoid “false positives,” space agencies must adhere to strict sterilization and contamination control protocols to ensure that Earth-based organic matter is not mistaken for Martian life. Those rules, coordinated internationally but implemented through national space legislation and export controls, now feed directly into mission cost estimates, spacecraft design and launch schedules.
The Rosalind Franklin mission’s focus on the Oxia Planum-a region rich in clays-is a strategic choice made at the intersection of science and policy. Clays are known to preserve organic molecules more effectively than other geological formations, increasing the probability that ancient biosignatures remain intact and that the mission can deliver a defensible scientific return on taxpayer investment.
By integrating high-precision chirality analysis directly into the rover’s hardware, ESA is reducing the risk of data degradation and contamination that occurs during sample return and the need for elaborate containment facilities governed by terrestrial biosecurity rules. This system design ensures that the evidence of past life, if it exists, is analyzed in its original environmental context-and in a way that can withstand the legal, political and scientific scrutiny that would inevitably follow any claim that Mars once hosted life.
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