Enceladus, a moon of Saturn, is a prime target in the hunt for life elsewhere in our solar system
NASA/JPL/Space Science Institute
A novel approach has been developed to identify the chemical characteristics of living organisms, offering a potential breakthrough in the detection of extraterrestrial life forms that may operate differently from those on Earth.
Traditionally, the search for alien life has relied on biosignatures, which are specific substances or patterns that serve as reliable indicators of the presence of living entities. Scientists often analyze the atmospheres of distant planets to detect molecular biosignatures. However, many molecules generated by living organisms can also be produced through geological or chemical processes in the absence of life forms.
The innovative method, pioneered by Christopher Carr and his team at the Georgia Institute of Technology, focuses on amino acids. Amino acids, the fundamental building blocks of proteins essential for all life on Earth, are relatively simple molecules that can exist independently of life, such as in lunar soil or on comets and meteorites.
Instead of merely identifying amino acids, Carr and his colleagues propose measuring the reactivity of these molecules within a sample as a more robust indicator of living organisms. In non-living systems, molecules react with external factors in their environment, leading to their formation and destruction. However, more reactive molecules are prone to disappear in such environments. Living systems, on the other hand, tend to retain highly reactive molecules as they are vital for the chemical processes supporting life, resulting in a distinct signature.
The reactivity of a compound is determined by the arrangement of electrons within the molecule. Molecules with higher reactivity exhibit a smaller energy difference between the outermost electron and the subsequent available space for an additional electron during a reaction.
By calculating this energy difference for 64 amino acids, including those not utilized by Earth’s life forms, and examining amino acid distributions in known samples from abiotic and living sources, Carr’s team could assess the statistical distribution of amino acid reactivities. This enabled them to assign a probability of whether a sample originated from a living or non-living source.
Testing this method on over 200 samples, the researchers achieved a 95% accuracy rate in identifying life forms. Carr emphasizes that since life elsewhere in the universe is likely based on carbon chemistry and amino acids, governed by similar chemical reactivity principles as life on Earth, this approach holds promise for detecting extraterrestrial life.
While the concept of using molecule reactivity to detect life is not new, the statistical distribution analysis introduced by Carr’s team represents a significant advancement, according to Henderson Cleaves from Howard University. This method could potentially be integrated into future space missions to celestial bodies like Mars or Saturn’s moons, such as Enceladus, although the requisite equipment for precise molecule measurement poses a challenge.
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