Patterns as biosignatures: What evidence reveals whether there were or still are extraterrestrial life forms on another planet? Astrobiologists have now found a new answer to this. According to this, biological life forms leave behind a characteristic distribution pattern of certain molecules such as amino acids or fatty acids. Their combination and frequencies show more reliably than individual molecules whether biological processes were at work, as the team explains in “Nature Astronomy”.
Whether on Mars, Jupiter’s moon Europa or life-friendly, Earth-like exoplanets: It is still unclear whether there is or was life elsewhere in space. However, it is very likely that Earth is not the only planet where life forms have evolved. But in order to prove extraterrestrial life, one needs clear biosignatures, for example in the form of chemical compounds that can only have arisen through biological processes.
Created by living beings or not?
However, therein lies the problem. There are many molecules that are considered to be the building blocks of life, including amino acids, DNA bases and certain fatty acids. “But these compounds are not exclusively of biological origin: they have now also been discovered in comets and meteorites, under simulated prebiotic conditions and in terrestrial environments in which abiotic synthesis would also be possible,” explain Gideon Yoffe from the Weizmann Institute of Science in Israel and his colleagues.
The NASA Mars rovers have already detected several organic molecules on Mars that could be of both geochemical and biological origin. In addition, the instruments of current space probes or telescopes are often not sufficient to determine, for example, the handedness or isotopic composition of extraterrestrial molecules – both of which can provide clues to the origin. The detection of potential building blocks for life on another celestial body is therefore not yet sufficient proof of extraterrestrial life.
“Astrobiology is similar to forensics in this respect: we try to infer processes based on incomplete traces and often very limited data,” says Yoffe.
It depends on the frequency
That’s why Yoffe and his team looked for a biosignature that can also be identified using current measuring instruments. They found what they were looking for when they examined the frequency and distribution of potential life building blocks in more detail. To do this, the astrobiologists used statistical methods that are used in ecology to assess species diversity. On the one hand, one looks at the species richness and thus how many species are present in an ecosystem. On the other hand, their frequency distribution is determined.
Chemical molecules on another celestial body can also be assessed in a similar way: if they were created biogenically, this is also revealed in their frequency distribution. “Life not only produces certain molecules, it also creates an organizational pattern that we can see through such statistical methods,” explains co-author Fabian Klenner from the University of California at Riverside.
What biogenic amino acids and fatty acids reveal
For example, when amino acids are created geochemically, simple, short-chain compounds dominate because they require less energy to synthesize. “However, biosynthesis can circumvent this hierarchy,” explain the researchers. “The control by enzymes allows organisms to produce even complex molecules in exactly the quantities required by their metabolism.” If amino acids in a sample come from living organisms, the proportion of longer-chain, more complex molecules would therefore have to be higher.
“An analogous principle applies to fatty acids: Organisms only produce a narrow range of molecular chain lengths, which they need, for example, for their membrane function,” the astrobiologists continued. Abiotic systems, on the other hand, show no such preference for certain chain lengths. Based on this finding, Yoffe and his team developed an index that can classify samples of these two types of molecules as biogenic or abiogenic based on their diversity and abundance.
The team then tested whether this pattern could be recognized using existing data using the amino acid and fatty acid composition of around 100 analysis data sets from microbes, fossils, soils, meteorites, asteroids and laboratory samples.
“Really surprising”
And in fact: the astrobiologists were able to distinguish between biological and non-biological samples based on the molecular pattern alone. “Two clearly distinguishable groups emerged,” reports the team. For the amino acids, biological samples showed a much more even distribution of the molecular sizes present. With fatty acids it was exactly the opposite: “Biological samples are more patchy and only contain a limited subset of chain lengths,” said Yoffe and his colleagues.
The clarity with which these differences in molecular distribution patterns were apparent amazed even the research team. “That was really surprising,” says Klenner. “The method not only showed the difference between life and non-life, but even revealed how severely the samples were degraded.” Although very old biological samples such as fossilized dinosaur eggshells were contaminated and mixed with sediment, the typical distribution pattern of amino acids and fatty acids could still be identified.
New tool for searching for life
According to astrobiologists, their method offers a good tool for searching for traces of extraterrestrial life. “This is another way to find out whether life once existed on a celestial body,” says Klenner. However, the researchers emphasize that their molecular biosignature alone is not enough to prove extraterrestrial life. “But if different techniques all point in the same direction, then that’s a strong statement,” says Klenner.
Another advantage: The distribution pattern of amino acids and fatty acids does not require any special analyses. Instruments such as the mass spectrometers of space probes or NASA’s Mars rovers can also carry out the necessary analyzes.
Source: Gideon Yoffe (Weizmann Institute of Science, Rehovot, Israel) et al., Nature Astronomy, 2026; doi: 10.1038/s41550-026-02864-z