Potential indicators of life on other planets can be created in a lab

NASA's James Webb Space Telescope launched in 2009. One of its missions is to capture images of exoplanets, planets outside of Earth's solar system, to understand different atmospheres. Part of the satellite's mission is to ask: Do these planets support life?

The new study looks at what happens in a planet's atmosphere when gases react with light and form an "organic haze and associated gases," aerosol particles formed via atmospheric chemistry. The authors focused on organic molecules that contain sulfur, including dimethyl sulfide, which are secondary metabolic products of living organisms on Earth.

"One of the big findings of the paper that we saw was dimethyl sulfide," said Reed. "That one was exciting, because it's been measured in exoplanetary atmospheres, and it's thought previously to be a sign of life living on the planet."

To recreate planetary atmospheres in a lab, Reed and Browne alongside co-authors, including CIRES associate director Maggie Tolbert and Visiting Fellow Shawn McGlynn, mimic atmospheres where light reacts with gases. In the new study, they used UV light to turn methane and hydrogen sulfide molecules into reactive species, which produce organosulfur gases - the biosignatures seen from the James Webb Space Telescope.

Reed noted that while the findings are exciting, they are limited to a singular type of atmosphere. "There's a wide variety of atmospheres, and we only looked at small differences in one - you can't study every atmosphere that exists in a lab," he said.

Looking forward, the researchers hope their study will inspire more fundamental laboratory studies looking at basic chemical reactions, especially with sulfur. Sulfur is challenging to work with - it's sticky, smelly, and toxic. But not studying sulfur reactions prevents scientists from fully understanding what these findings mean about biosignatures.

"When we're searching for these biosignatures, the tendency is to want to sensationalize 'we detected signs of life,'" Browne said. "The atmosphere is really good at making a whole bunch of different molecules, and we've found that just because it can be made in a lab, doesn't mean it's not a source."