The observable universe. (Illustration: Pablo Carlos Budassi / Wikipedia)

Living things leave behind tell-tale signs of their existence: fossilized bones, DNA, the chemical byproducts of metabolism. Living things on Earth, that is. There currently exists no predictive theory to completely guide astrobiologists searching for life beyond our planet, where the chemical signatures of life, and the geo- and atmospheric chemistries under which it evolved, might look quite different from Earth.

In early November, NASA’s Astrobiology Program launched the new Interdisciplinary Consortia for Astrobiology Research (ICAR), supporting eight teams focusing on specific outstanding questions in astrobiology. SFI External Professor Sara Walker (Arizona State University) is leading one of the teams, an interdisciplinary group of theorists and experimentalists whose expertise in geochemistry, microbiology, exoplanet atmospheres, network theory, and complex systems will help them explore the question: What detectable universal patterns distinguish living chemistries across diverse planetary environments?

Answering this question, Walker says, will help astrobiologists develop a theoretical framework to refine their search for extraterrestrial life, and to be able to recognize life as we don’t know it.

“So far, astrobiology has been really focused on the looking for chemistry of life as we know it — amino acids, metabolic bi-products like oxygen or methane,” says Walker. “What we’re trying to do is say that life is not a property of individual molecules; it’s a systems-level property that emerges from the interactions of many molecules and reactions. We want to understand and quantify the patterns in those molecules and reactions, then use those as new predictors of biosignatures.”

The team will build on SFI-related research on scaling laws and use techniques from complex systems science — tools that are fairly new in astrobiology. SFI Professor Chris Kempes, who is already leading a NASA Astrobiology Research Coordination Network, has worked on identifying scaling laws and regularity in life on Earth, is part of Walker’s ICAR team. He hopes to uncover the mechanisms that lead to scaling relationships as well as other biochemical and physiological properties of life. “Finding those mechanisms will be really essential for understanding whether certain properties or behaviors are really universal or not,” he says. 

As the team studies universal patterns on Earth, they plan to consider its biosphere as a multilayered network, where the atmospheric, geochemical, and biochemical networks interact as a coupled system. “The importance of this approach is highlighted by the recent phosphine-on-Venus debate,” says Kempes. “Phosphine was detected on Venus, and the question becomes: Is it a biosignature — for Venus? In general? — and is it likely to be a false positive or a false negative? To get at those questions, you need to understand the planet’s coupled networks and how different they might be with or without life in the loop.”

Walker adds, “If we are to ever unambiguously detect alien life, or even know how to properly look for it, we need quantitative frameworks. We need proper theory that allows us to know what life is. The tools to do that naturally come from complex systems research.”