When it comes to the search for life elsewhere in the universe, methane and other chemical compounds are seen as signs of biology because they are often produced by living microbes. However, scientists can be misled because certain geological processes can produce chemical signatures identical to those of living organisms.
To help identify true biological signals and reduce the risk of false detections, researchers have developed a framework that models what a planet’s chemistry looks like without life.
Their research is published in the journal Nature Astronomy.
The methane problem
Icy ocean worlds like Saturn’s moon Enceladus and Jupiter’s moon Europa are prime targets in the search for alien life because they have liquid oceans under their ice shells. These are believed to have the internal heat and chemical energy needed to support living things.
However, if scientists detect methane in these hidden oceans, it won’t necessarily mean they have found life because methane can also be produced by nonbiological chemical reactions between water and rocks, and other geological processes.
“Ocean worlds are important targets for life detection missions… However, identifying potential life requires observing clear and unambiguous biosignature signals above the baseline of existing abiotic processes…,” the researchers wrote in their paper.
Space agencies are designing and building sensitive instruments to detect potential biosignatures, such as methane and carbon isotopes, during future missions. But without a strict baseline of what a planet or moon produces naturally, they won’t be able to tell if what they have found is truly front-page news. This framework gives scientists a tool to calculate the natural background chemistry so they can spot when a signal is truly unusual.
To develop their model, the research team used Enceladus as a case study. They tracked how chemical compounds and their isotopic signatures move from the rocky seafloor, through miles of ocean water and out into space.
They focused on two main potential signs of life. The first was methane carbon isotopes. Living microbes often produce methane with a different carbon isotope balance than many nonbiological processes because they preferentially use the lighter carbon-12 isotope.
Second, they looked at amino acid handedness. These are the building blocks of life and, when made by biology, are almost exclusively “left-handed,” meaning their molecular shape has one preferred orientation. The team modeled how long it takes for these left-handed shapes to degrade and scramble back into a random mix while floating in an alien ocean.
Testing the model
The team tested their model using real chemical data collected from Enceladus by past space missions, together with computer models. They wanted to see whether their framework could distinguish between biological and geological sources of these chemical signatures.
They found that, based on current understanding of Enceladus, some geological processes could produce methane isotope signatures that overlap with those expected from living microbes, making it difficult to distinguish between the two. For amino acids, they discovered the opposite problem. Ocean heat can scramble their left-handed shapes into a random mix in as little as about 100 to 10,000 years, which could erase evidence of life.
While scientists already knew that biology and geology could produce similar chemical signatures, they had no reliable way to measure how much they overlapped. This new framework helps predict what a lifeless world would look like, making it easier to determine what additional evidence is needed before claiming a discovery.
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Publication details
Peter M. Higgins et al, A framework for evaluating biosignature potential against the abiotic baseline on ocean worlds, Nature Astronomy (2026). DOI: 10.1038/s41550-026-02893-8
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Baseline tool could separate alien life signals from geology on ocean worlds (2026, July 7)
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