ExoMars: Stress Test For Search For Life

The ESA Mars rover Rosalind Franklin is scheduled to analyze soil samples on Mars in 2030. Researchers have successfully prepared for this mission through laboratory analyses of meteorites

To the point

• Mars mission: Starting in 2030, ESA’s rover Rosalind Franklin will search for traces of life on Mars. The MPS is contributing a scientific instrument to the mission.
• Traces of life: The instrument determines, among other things, a crucial property of organic molecules: their chirality. This reveals whether the molecules were ever part of a living organism.
• “Feasibility study”: In preparation, researchers have successfully used this principle for the first time to analyse two particularly relevant chemical compounds in meteorite samples.
• Polluted Earth’s Atmosphere: Remnants of burnt fossil fuels in Earth’s atmosphere have led to measurable changes in the composition of the meteorite, which were detected during tests of the Mars rover’s instrument: The meteorite must have “picked up” traces of fossil fuels as it plunged through Earth’s atmosphere.

Billions of years ago, environmental conditions on Mars were significantly more favorable than they are today. Our neighboring planet was likely warm, humid, and surrounded by a dense atmosphere back then. Whether simple microorganisms could have developed at that time remains an open question. Although NASA rovers have found organic molecules in Martian rocks, none of them can be definitively linked to life. In 2025, researchers photographed small spots on a rock formation in Jezero Crater that resemble a leopard’s spots. The structures could be of organic or microbial origin; a soil sample was collected. However, the samples must first be analyzed on Earth before it can be confirmed or ruled out with certainty whether these are indeed remnants of past life on Mars. Due to a lack of funding, the return of the samples has currently (as of June 2026) been removed from NASA’s agenda.

The Mars rover Rosalind Franklin, part of the European Space Agency’s (ESA) ExoMars program, took a different approach from the outset to find life on Mars. Starting in 2030, it will reinforce the “search team” on Mars. Among other things, the European rover is specialized in detecting organic molecules in the Oxia Planum region near the equator. The clay-rich geology suggests that water once flowed there. Researchers from the Max Planck Institute for Solar System Research, the University of Göttingen, and the University of Côte d’Azur in Nice (France) are working on the underlying measurement method using the Mars Organic Molecule Analyser (MOMA), an instrument developed and built under the leadership of the Max Planck Institute in Göttingen. They have now successfully tested the method using a fragment of Mars-a Martian meteorite.

Proving that life once existed on Mars is a difficult task, even for ESA’s rover. How can organic molecules that were part of an organism billions of years ago be distinguished from those that formed by non-biological processes? And which molecules are particularly suited to revealing their past? The researchers are pinning their hopes on pristane (C19H40) and phytane (C20H42), two hydrocarbons that derive from living organisms and occur on Earth as components of petroleum. They are particularly stable. “If life once existed on Mars, then molecules like pristane and phytane represent important molecular biosignatures that could have survived to this day,” said MPS scientist Guillaume Leseigneur, lead author of the new study.

Mirrored molecules

Another property makes pristane and phytane promising indicators of life: like many other organic compounds, they are chiral, meaning that they can exist in different configurations, known as enantiomers. These differ only in the spatial, mirrored arrangement of their atoms within the molecule – a bit like the fingers of the left and right hands. “Chirality is a valuable tool in the search for past extraterrestrial life,” said co-author Uwe Meierhenrich of Côte d’Azur University. In organisms, chiral organic molecules occur almost exclusively in one of the two possible mirror configurations. This is true on Earth – and, due to life’s self-replicative properties, must also apply to any potential extraterrestrial life. However, if the same molecules are of non-living origin, both mirror forms are expected to be present in equal parts.

Meteorite and Mars Substitute

The Rosalind Franklin rover is capable of distinguishing between organic molecules of different chirality. This task is performed by the Mars Organic Molecule Analyzer (MOMA), an instrument that combines a gas chromatograph, a mass spectrometer, small furnaces, and an excitation laser. Using the gas chromatograph and mass spectrometer, the instrument analyzes the volatile components of rock samples that have been heated in the furnaces. The resulting gas mixture then passes through various capillary tubes that have been coated on their inner surfaces. Since chiral variants of the same type of molecule react at different rates with the coatings, they can be separated in time.

In the current measurements, for which the team used identical MOMA tube replicas, this has now been achieved for pristane and phytane for the first time. Both substances are extremely unreactive. “Chiral separation of pristane and phytane requires high instrument sensitivity and measurement accuracy, both of which we show MOMA can achieve”, explained co-author and MOMA team member Fatma Yesil Sahan from the MPS. As a substitute for Martian rock, the researchers used samples from the Murchison meteorite, which fell in Australia in 1969. Like other space rocks, it contains a variety of organic molecules: some that are part of its original composition, and others that were added through biological contamination, for example at the site where it was found. The researchers assumed that pristane and phytane likely belong to the latter group.

Fossil fuels in Earth’s atmosphere have contaminated Martian meteorites

However, the results of the measurements were surprising: the Murchison meteorite contains all chiral variants of pristane and phytane in equal proportions – quite unlike any biomass it could have come into contact with at its discovery site. The researchers concluded that the contaminants must have been picked up during its descent through the atmosphere by contact with aerosols from fossil fuel burning. This is suggested by comparative measurements of pristane and phytane preserved in oil shales, sedimentary rocks containing a petroleum precursor. “Petroleum forms in these rocks over millions of years at great depths under the influence of heat and pressure”, said co-author Manuel Reinhardt from the University of Göttingen. Under such conditions, the chiral imbalance is lost, which plausibly explains the equal proportions of all chiral variants of pristane and phytane in the Murchison meteorite.

The research team views the new measurements not only as a successful trial run for MOMA’s activities on Mars. Rather, the results also raise further questions about the origin of organic molecules found in meteorites, and about the increasing concentrations of petroleum contamination in our atmosphere.

BK/MPS and BEU/MPG