How to Search for Life as we Don’t Know it

The field of extrasolar planet studies has come a long way in recent years. Astronomers have confirmed the existence of 4,935 exoplanets in 3,706 star systems, with another 8,709 candidates waiting to be confirmed. The focus is transitioning from discovery to characterization with so many planets to study. The fields are going to advance a lot farther now that the James Webb Space Telescope has been deployed.

Scientists anticipate that the characterization of planetary atmospheres may lead to the discovery of signs associated with life and biological processes. The challenge will be how to recognize signatures that don't conform to life as we know it.

For the sake of their study, the team looked to the various processes that we associate with life here on Earth and attempted to identify the universal patterns that don't appear to depend on specific molecules. The interplay of hundreds of chemical compounds and reactions, some of which are shared by all organisms, emerges life on Earth. The study of life beyond Earth raises problems because of this universal biochemistry.

In other planetary environments, the emergence and evolution of life may come down to different chemical elements. The basic building block of life could be germanium or Silicon. Instead of water, organisms could use solvent like methane or ammonia. There are certain biological processes associated with life that could be shared between life on Earth and elsewhere in the Universe.

Future surveys could find evidence of life beyond Earth if they focused on what it does rather than what it is. Sara Imari Walker is the deputy director of the Beyond Center and an associate professor with the School of Complex adaptive systems.

“We want to have new tools for identifying and even predicting features of life as we don’t know it. To do so, we are aiming to identify the universal laws that should apply to any biochemical system. This includes developing quantitative theory for the origins of life, and using theory and statistics to guide our search for life on other planets.”

“We are not just the molecules that are part of our bodies; we, as living things, are an emergent property of the interactions of the many molecules we are made of. What our work is doing is aiming to develop ways of turning that philosophical insight into testable scientific hypotheses.”

The study's lead author was a graduate of Arizona State University. Walker and Gagler decided to focus on the function of the enzymes. The Integrated Microbial Genomes and Microbiomes database is maintained by the DOE and the Joint Genome Institute.

Eukarya are cells that have a nucleus enclosed within a nuclear envelope and include everything from protists and fungi to plants and animals. Through this approach, the team looked at the majority of Earth's biochemistry and identified statistical patterns in the biochemical function of enzymes.

In doing so, they verified that statistical patterns originated from functional principles that can't be explained by the common set of enzyme functions used by all known life and identified scaling relationships associated with general types of functions.

“We identified this new kind of biochemical universality from the large-scale statistical patterns of biochemistry and found they are more generalizable to unknown forms of life compared to the traditional one described by the specific molecules and reactions that are common to all life on Earth. This discovery enables us to develop a new theory for the general rules of life, which can guide us in the search for novel examples of life.”

The team is funded through the NASA Astrobiology Program. The program was inaugurated last year and selected eight research teams to investigate topics such as the origins and evolution of life, and the search for life beyond Earth. The main investigator of the team is Walker.

In addition to researchers with SESE, the team included members from the Santa Fe Institute in New Mexico. The paper that describes their findings was published in the Proceedings of the National Academy of Sciences.

Further reading: PNAS.