Scientists have developed a test based on the reactivity of amino acids that could identify alien life differing from Earth-based organisms. The approach analyzes molecular energy differences to distinguish living from non-living samples with high accuracy. This tool may aid future missions to Mars or Saturn's moons.
A team led by Christopher Carr at the Georgia Institute of Technology has proposed a method to detect life on other worlds by examining the reactivity of carbon-based compounds, particularly amino acids. Amino acids serve as building blocks for proteins essential to Earth life, but they also appear in non-biological settings, such as lunar soil, comets, and meteorites.
The innovation lies in assessing not just the presence of these molecules, but their reactivity patterns. In non-living environments, more reactive molecules tend to degrade faster due to interactions with cosmic rays or other elements. Living systems, however, preserve these reactive molecules for vital chemical processes, creating a distinct signature. As Carr explains, “If you don’t have a system in place to maintain what’s present, then the things that will tend to be destroyed would be those that are more reactive.”
Reactivity is quantified by the energy difference between a molecule's outermost electron and the next available orbital; smaller differences indicate higher reactivity. The researchers calculated this for 64 amino acids, including those not used by Earth life. They then analyzed abundances in over 200 samples from abiotic sources like meteorites and biotic ones like fungi and bacteria, mapping statistical distributions to assign probabilities of life presence.
The test achieved 95 percent accuracy in classifying samples. “The beauty of this approach is that it’s incredibly simple,” Carr notes. “It’s highly explainable and it’s linked directly to physics.” Carr argues that extraterrestrial life, if carbon-based, would follow similar reactivity principles, as “Life inherently needs to control when, how and where molecules interact and reactions take place, so that is going to involve having structures that can regulate the flow of electrons and how things interact electrically.”
Henderson Cleaves at Howard University praises the statistical distribution aspect as novel, though he cautions that implementation on missions to Mars or Enceladus would require precise molecular measurement equipment. The work is detailed in a preprint on arXiv (DOI: 10.48550/arXiv.2602.18490).