Researchers Discover Certain Biosignatures Might Not Signify Life, Challenging Prevailing Beliefs.
An effective way to assess the possibility of life on distant planets — those in other solar systems orbiting different stars — is to analyze their atmospheres. Telescopic observations frequently reveal traces of gases which could suggest the presence of life and potential habitability. However, a recent study from the University of Colorado Boulder contests this viewpoint: researchers have synthesized a specific gas associated with life in a laboratory without any organisms involved.
This research, published today in Astrophysical Journal Letters, indicates that one molecule, often interpreted as a biosignature or sign of life, may not be as definitive an indicator of life as previously asserted. The scientists successfully produced dimethyl sulfide, an organic sulfur compound commonly generated by marine microorganisms, in a reaction chamber using light and gases typically found in the atmospheres of various planets.
While the ability to fabricate dimethyl sulfide in a lab was an exciting breakthrough, the results upend established theories regarding its significance. This work is led by Nate Reed, a Visiting Fellow at CU Boulder’s Cooperative Institute for Research in Environmental Sciences (CIRES), along with CIRES Fellow and associate professor of chemistry Ellie Browne.
“The sulfur compounds we are creating are associated with life, as they are produced by organisms on Earth,” Browne explained. “However, we generated them in the lab without any biological presence, suggesting they may not necessarily indicate life but could signify environments suitable for life.” The study suggests that organic sulfur compounds should be regarded more as signals of metabolic potential rather than definitive biomarkers.
Searching for Life
Launched in 2009, NASA’s James Webb Space Telescope aims to capture images of exoplanets—planets beyond our solar system—to explore their atmospheres. A key question of the satellite’s mission is whether these planets can support life.
The latest study investigates what occurs in a planet’s atmosphere when gases interact with light, resulting in the formation of “organic haze and associated gases,” or aerosol particles formed through atmospheric chemistry. The researchers focused on organic molecules that contain sulfur, such as dimethyl sulfide, which are byproducts of metabolism in living organisms on Earth.
“A significant finding was the production of dimethyl sulfide,” Reed noted. “This discovery is intriguing because it has been detected in exoplanetary atmospheres and was previously believed to be indicative of life present on the planet.”
To recreate the conditions of planetary atmospheres in the lab, Reed, Browne, and their collaborators, including CIRES associate director Maggie Tolbert, simulated environments where light reacts with gases. For this study, they used UV light to convert methane and hydrogen sulfide molecules into reactive species that yield organosulfur gases — the biosignatures detectable by the James Webb Space Telescope.
Although these findings are promising, Reed pointed out that they pertain to just a specific type of atmosphere. “There is a vast diversity of atmospheres, and we only examined a few variations of one — it’s impossible to analyze every atmospheric type in a laboratory,” he said.
Looking ahead, the researchers hope this study will encourage more fundamental laboratory investigations focused on basic chemical reactions, particularly involving sulfur. Working with sulfur is complex due to its sticky, odorous, and toxic nature. However, neglecting sulfur reactions hinders a comprehensive understanding of the implications these findings hold for biosignatures.
“When we search for biosignatures, there’s a tendency to exaggerate ‘we found signs of life,'” Browne stated. “The atmosphere is adept at generating a wide range of molecules, and we’ve learned that simply because something can be produced in a laboratory doesn’t mean it is not indicative of biological potential.”
