Chemical Complexity as a Sign of Life as We Don’t Know It

When looking for signs of life elsewhere in the Universe, how limited are we by what we know of the biology of life here on Earth? Is our familiarity with Earth-based biological molecules and biochemical mechanisms such as deoxyribonucleic acid (DNA) or adenosine triphosphate (ATP) preventing us from seeing evidence of biological systems of life as we don’t know it? Astrobiologists are working to develop methods for detecting signatures of life that are indifferent (or “agnostic”) to the biological and biochemical ways of the life that created that signature, meaning, we don’t have to understand those ways to know that life very likely created that signature.

One type of biosignature is the phenomenon of chemical complexity. The more complex the structure of a chemical or molecular compound is, the less likely it is to have formed without being part of a biological system. A team of astrobiologists, led from the University of Glasgow and including NASA Astrobiology Program researchers at NASA’s Goddard Space Flight Center and Arizona State University, has developed a new system for measuring and quantifying chemical complexity that can be used to analyze Earth-based samples as well as those collected from elsewhere, including planets and moons. Their system uses mass spectrometry to compute a threshold of complexity, over which the compounds are extremely unlikely to form without supporting biological machinery.

Their study and results appear in today’s issue of Nature Communications.