Was there once life on Mars? And could chemical relics of this still be found today? An experiment carried out by the Mars rover “Curiosity” now provides a possible answer to this. He subjected samples of clayey sandstones in Gale Crater to special analysis and identified more than 20 different organic molecules. Among these are ring-shaped hydrocarbons and nitrogen-containing compounds that could come from precursors of life’s building blocks. This does not prove that there was once biological life on Mars. But it shows that organic relics can survive for more than 3.5 billion years despite harsh radiation and the chemically aggressive regolith on the planet. This raises hope for further discoveries.
In its early days, Mars was relatively similar to Earth: it had lakes, rivers and perhaps even an ocean, and its climate was much milder than today. Theoretically, simple life, for example in the form of microbes, could have once arisen on our cooler neighboring planet. To find out whether this was the case, NASA sent two “rolling chemistry laboratories” to the Red Planet: the Mars rover Curiosity, which landed in Gale Crater in 2012, and the Mars rover Perseverance, which has been active in Jezero Crater since 2021. Both rovers are equipped with various analysis instruments and reaction chambers with which they can chemically analyze dust and rock samples. Both rovers found what they were looking for: They have already detected various organic molecules on Mars, including chlorobenzene, naphthalene, thiophene and dimethyl sulfate. Hydrocarbon chains up to twelve carbon atoms long were also included.
Lots of aromatic hydrocarbons
Now the Curiosity rover has detected additional organic molecule variants using a special experiment. The instrument
SAM, short for Sample Analysis at Mars, can break down complex molecules from the Martian material into smaller, gaseous compounds in a special reaction chamber using the solvent tetramethylammonium hydroxide (TMAH). These are then sucked in by a gas chromatography-mass spectrometer (GC-MS) and analyzed for their components. Because the rover only carries two portions of the solvent on board, NASA has to carefully select which samples it subjects to this experiment. In 2020, the choice fell on the Glen Torridon region in Gale Crater – a clayey sandstone formation that was formed by deposits from an ancient Martian lake.
The results of this analysis are now available. “The resulting molecules are products of the first thermochemolysis experiment conducted in situ on another planetary body,” report Amy Williams from the University of Florida and her colleagues. In total, the SAM experiment detected more than 20 different organic molecules from the sample. These include ring-shaped hydrocarbons such as trimethylbenzene, methylbenzene, naphthalene and other ring molecules with various appendages. “16 peaks in the gas chromatograph could not be clearly identified,” report the researchers. However, from the molecular weight and the elemental components, they conclude that these are further variants of hydrocarbon compounds with one or two rings. Some of these molecules suggest that the sample examined by Curiosity originally contained even more complex organic compounds. “The methylated benzene and naphthalene compounds indicate that a larger macromolecular structure has been disrupted by TMAH thermochemolysis,” write Williams and her team.
“Fundamental component of astrobiologically relevant molecules”
However, a molecule detected as peak 22 in the analysis curves is particularly exciting, as the researchers explain. This could be a heterocyclic amine from the indole group. These aromatic hydrocarbons consist of two connected rings in which nitrogen atoms are part of the ring structure. Some other peaks in the SAM analyzes could also originate from such nitrogen-containing heterocycles. “This is an exciting possibility because nitrogen heterocycles are fundamental components of astrobiologically relevant molecules such as nucleic acids,” explain Williams and her colleagues. Also new for Mars is the detection of benzothiophene, a sulfur-containing double ring molecule. “Benzothiophene is a known component of carbon-containing macromolecules from meteorites,” the team writes. The substance could therefore have arrived on early Mars with meteorites – possibly as part of the chemical building blocks of life. “Its detection represents the largest undegraded aromatic molecule discovered on Mars to date,” said the researchers.
But what does this evidence mean for Mars and its potentially life-friendly past? According to the researchers, these finds show two things: On the one hand, they prove that there are also more complex organic compounds on Mars – and that they may have arisen from even larger macromolecules. “We could be seeing organic material here that has been preserved on Mars for 3.5 billion years – despite geological transformation processes and hard radiation,” says Williams. “This demonstrates that it may be possible to search for evidence of past life in the form of organic relics.” However, it cannot be determined based on the SAM analyzes alone, as the researchers explain, whether the molecules now detected were created biologically or geochemically. This could only be shown by the samples that the Perseverance rover collected and which are to be returned to Earth in a future Mars mission.
Source: Amy Williams (University of Florida, Gainesville) et al., Nature Communications, doi: 10.1038/s41467-026-70656-0