New method sharpens the search for alien biology

For decades, the search for life beyond Earth has revolved around a key question: What molecules should scientists be looking for on other planets or moons?

A new study, published in Nature Astronomy, suggests the more revealing clue may not be the molecules themselves, but the hidden order connecting them.

"We're showing that life does not only produce molecules," said Fabian Klenner, UC Riverside assistant professor of planetary sciences and co-author of the study. "Life also produces an organizational principle that we can see by applying statistics."

The researchers found that amino acids are consistently more diverse and more evenly distributed in a material sample created by a living thing than those found in abiotic or nonliving things. In contrast, the pattern reverses for fatty acids: abiotically produced fatty acids are distributed more evenly than those produced by biological processes.

This study is the first to demonstrate that this fundamental principle of life can be detected using a statistical approach that does not rely on any one special instrument. Instead, it may be possible to find this pattern in data collected by instruments already aboard current and planned space missions.

The work arrives as planetary exploration enters a new phase in which longstanding questions about the origin of life and its prevalence in the universe may finally become testable with real observational data. Missions to Mars, Europa, Enceladus, and other worlds are returning increasingly sophisticated measurements of organic chemistry. Yet interpreting those measurements remains difficult.

Many compounds central to terrestrial biology, including amino acids and fatty acids, can also form through nonbiological processes. They have been detected in meteorites and synthesized in laboratory experiments designed to mimic conditions in space. Finding such molecules alone is not enough to claim evidence of life.

"Astrobiology is fundamentally a forensic science," said Gideon Yoffe, postdoctoral researcher at the Weizmann Institute of Science in Israel and first author of the study. "We're trying to infer processes from incomplete clues, often with very limited data collected by missions that are extraordinarily expensive and infrequent."

The researchers approached the problem with a statistical framework borrowed from ecology, where scientists quantify biodiversity by measuring two properties: richness, or how many species are present, and evenness, or how uniformly they are distributed.

Yoffe first encountered the approach while completing doctoral work in statistics and data science, where diversity metrics were used to uncover patterns in complex datasets, including studies of ancient human cultures. The team applied the same logic to extraterrestrial chemistry.

Using approximately 100 existing datasets, the researchers analyzed amino acids and fatty acids from microbes, soils, fossils, meteorites, asteroids, and synthetic laboratory samples. Biological samples repeatedly exhibited distinct organizational patterns that separated them from nonliving chemistry.

What surprised the researchers most was the method's strength despite its simplicity.

Looking at the samples in this way, the researchers were consistently able to separate biological and abiotic samples with striking reliability. In addition, they were also able to see that biologically derived materials formed a continuum from well-preserved to degraded states.

"That was genuinely surprising," Klenner said. "The method captured not only the distinction between life and nonlife, but also degrees of preservation and alteration."

Even heavily degraded biological samples retained traces of that organization. Fossilized dinosaur eggshells analyzed in the study, for example, still carried detectable statistical signatures shaped by ancient life.

The researchers emphasize that no single method is likely to prove the existence of extraterrestrial life on its own.

"Any future claim of having found life would require multiple independent lines of evidence, interpreted within the geological and chemical context of a planetary environment," Klenner said.

Still, the team believes their framework could become an important new tool for future missions.

"Our approach is one more way to assess whether life may have been there," Klenner said. "And if different techniques all point in the same direction, then that becomes very powerful."

(Cover image of the solar system: NASA)