Expanding the search for extraterrestrial life

In the quest for extraterrestrial life, telescopes have been our biggest allies, revealing new clues about how and where to search.

For example, powerful tools like the James Webb Space Telescope make it possible to study a planet’s atmosphere, where gases may serve as indicators of life, or “biosignatures.”

Biosignatures of extraterrestrial life

Traditionally, certain gases have been considered as potential biosignatures that provide scientific evidence of past or present life.

While sulfur compounds have been viewed as robust biomarkers, a recent study challenges this assumption.

In a game-changing turn of events, scientists at the University of Colorado Boulder have created dimethyl sulfide, an organic sulfur compound often made by marine microbes, in a chemistry lab without any living organisms.

Creating dimethyl sulfide in the lab

Dimethyl sulfide is a type of molecule that scientists typically view as a sign of life. The researchers said creating dimethyl sulfide in the lab was exciting, but their findings flip previous research on its head.

The study was led by Nate Reed, a visiting fellow at CU Boulder’s Cooperative Institute for Research in Environmental Sciences (CIRES), and Ellie Browne, CIRES Fellow and associate professor of chemistry.

The experts used light and gases found in many planets’ atmospheres to create this molecule, and their results suggest that organic sulfur compounds might not be robust biomarkers after all.

“The sulfur molecules that we’re making are thought to be indicators of life because they’re produced by life on Earth,” said Browne. “But we made them in the lab without life – so it might not be a sign of life, but could be a sign of something hospitable for life.” 

Searching for signs of life on exoplanets

The implications of this research are significant. What does it mean for the search for life on other planets? Could these compounds serve as markers of metabolic potential instead?

NASA’s James Webb Space Telescope, launched in 2009, has been helping us understand different planetary atmospheres and their potential to support life.

One of the primary objectives of this satellite mission is to capture images of exoplanets (planets outside Earth’s solar system) and study atmospheres for signs of life.

Detecting extraterrestrial life

The researchers also explored what happens in a planet’s atmosphere when gases react with light, forming an “organic haze and associated gases.” These are aerosol particles formed via atmospheric chemistry.

The study was focused on organic molecules containing sulfur, including dimethyl sulfide, which are secondary metabolic products of living organisms on Earth.

While the results are intriguing, Reed noted that they relate to just one 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.

The researchers hope their work will inspire more basic chemical reaction studies, particularly involving sulfur, despite its challenging characteristics.

Reevaluating what makes planets habitable

The findings highlight the need for a reevaluation of how scientists interpret biosignatures in extraterrestrial atmospheres.

Future research will need to explore a wider range of atmospheric conditions, perhaps integrating advanced computational modeling with empirical laboratory studies.

By challenging the traditional indicators of life, this research pushes the scientific community to redefine what makes an environment “habitable.”

Current criteria often emphasize the presence of water and specific gases associated with life as we know it. However, as this study reveals, some of these elements may originate from non-biological processes, thereby expanding the scope of what is considered potentially habitable.

New perspective on biosignatures

Scientists are now encouraged to consider a broader spectrum of environmental conditions to expand the search for extraterrestrial life beyond our current paradigm.

“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.”

The study is published in The Astrophysical Journal Letters.

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