For decades, the search for life beyond Earth has revolved around a key question: what molecules should scientists look for on other planets or moons? New research suggests that the key clue may not lie in the molecules themselves, but in the underlying order that binds them together.
Distribution of molecules matters
Fabian Klenner, an associate professor in the Department of Planetary Sciences at the University of California, Riverside, and a co-author of the study, notes that life not only creates molecules but also establishes an organizational principle that can be identified using statistical methods.
Researchers have found that the amino acids in a sample of a substance produced by living organism are significantly more diverse and evenly distributed than those found in abiotic or non-living objects. In the case of fatty acids, the situation is the opposite: abiotically formed 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 identified using a statistical approach that does not rely on any specific instrument. Instead, it may be possible to detect this pattern in data collected by instruments already on board current and planned space missions.
Measurements of organic chemistry in space missions
This work comes at a time when planetary research is entering a new phase, in which long-standing questions about the origin of life and its distribution throughout the Universe can finally be tested using actual observational data. Missions to Mars, Europa, Enceladus, and other worlds are returning increasingly sophisticated measurements of organic chemistry. However, interpreting these measurements remains challenging.
Many compounds that play a key role in biology on Earth—in particular, amino acids and fatty acids—can also be formed through nonbiological processes. They have been detected in meteorites and synthesized in laboratory experiments designed to replicate the conditions found in space. The fact that such molecules have been detected is not sufficient to claim that there is evidence of life.
Application of a statistical method
The researchers approached the problem using a statistical model borrowed from ecology, in which scientists quantify biodiversity by measuring two properties: richness, or the number of species present, and evenness, or how evenly they are distributed.
Yoffe, one of the study’s authors, first encountered this approach while writing his doctoral thesis on statistics and data science, where diversity metrics were used to identify 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 derived from microorganisms, soils, fossils, meteorites, asteroids, and synthetic laboratory samples. Biological samples have repeatedly demonstrated clear patterns of organization that distinguish them from inanimate chemistry. What surprised researchers most was the method’s effectiveness, despite its simplicity.
By examining the samples in this way, the researchers were able to consistently distinguish biological samples from abiotic ones with remarkable accuracy. In addition, they determined that the biological materials spanned a continuous spectrum 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 severely degraded biological samples retained traces of such organization. For example, the fossilized dinosaur eggshells analyzed in the study still contained detectable statistical patterns formed by ancient life.
New tool for detecting extraterrestrial life
Researchers observe that no individual method is likely to be sufficient on its own to establish the existence of extraterrestrial life.
“Any future claim of detecting life will require numerous independent pieces of evidence, which must be interpreted within the geological and chemical context of the planetary environment,” Klenner noted.
However, the team believes that the methodology they have developed could become an important new tool for future missions. It is a new approach that enables assessing whether life could have existed somewhere in space. If different methods point to the same conclusion, this will lend them considerable weight.
According to phys.org
