A recent study published in Nature has provided new insight into the presence of silicon in the atmospheres of gas giants like Jupiter and Saturn. The research, which used data from NASA’s James Webb Space Telescope, focused on a brown dwarf known as “The Accident,” discovered in 2020 by a citizen scientist involved with the Backyard Worlds: Planet 9 project.
Brown dwarfs are objects that exist between planets and stars. The Accident stands out because it shows characteristics found both in young and old brown dwarfs, making it difficult to detect through standard methods. Its faintness required the use of NASA’s most advanced observatory, Webb, to analyze its atmosphere.
Researchers identified a molecule called silane (SiH4) in The Accident’s atmosphere. This is notable because scientists have long expected to find silane in gas giants’ atmospheres but had not previously detected it. Michael Line, an associate professor at Arizona State University’s School of Earth and Space Exploration, led the identification process.
“We searched for a wide range of candidate molecules, but only silane consistently matched the specific features we saw in the Webb data,” co-author Line said. “That moment of realization was exhilarating — I love the thrill of discovery in the treasure trove of JWST observations of distant worlds.”
Silicon is believed to be present in Jupiter and Saturn but likely exists deep within their atmospheres as oxides such as quartz, which form cloud layers below those made up of water vapor and ammonia. This makes them hard to detect even with close-range spacecraft observations. Some scientists theorize that lighter silicon molecules like silane should be present higher up but have not been found until now.
“Sometimes it’s the extreme objects that help us understand what’s happening in the average ones,” said Jacqueline Faherty from the American Museum of Natural History and lead author on the study.
The Accident is estimated to be between 10 billion and 13 billion years old, making it one of the oldest known brown dwarfs. At its formation, there was less oxygen available compared to more recently formed celestial bodies. This scarcity meant that silicon bonded with hydrogen rather than oxygen, resulting in detectable silane.
Webb’s findings confirm that silane can form under these conditions and suggest why it is missing elsewhere: when enough oxygen is present, silicon tends to bond with it instead of hydrogen.
Line added that understanding how silane forms could help researchers studying other types of planets: “Silane is also predicted to be a byproduct of atmosphere-interior interactions in sub-Neptune-type planets with vast magma oceans hidden beneath thick atmospheres,” he said. “By understanding the conditions under which silane can arise in hydrogen-rich worlds like brown dwarfs, we gain critical context for how and when it might appear in the more observationally challenging atmospheres of exoplanets.”
Peter Eisenhardt from NASA’s Jet Propulsion Laboratory described The Accident as a natural experiment showing what happens when planets or brown dwarfs form with very little oxygen: “We can’t change the atmospheres of Jupiter or Saturn, but these objects show us what those planets might look like with different conditions — in this case, what happens when a planet or a brown dwarf forms with essentially no oxygen.”
Brown dwarfs are easier targets for atmospheric studies than gas giant exoplanets because they do not orbit stars whose light would obscure their own signatures. Insights gained from these objects may also help future studies searching for signs related to habitability on distant worlds.
“To be clear, we’re not finding life on brown dwarfs,” Faherty said. “But at a high level, by studying all of this variety and complexity in planetary atmospheres, we’re setting up the scientists who are one day going to have to do this kind of chemical analysis for rocky, potentially Earth-like planets. It might not specifically involve silicon, but they’re going to get data that is complicated and confusing and doesn’t fit their models, just like we are. They’ll have to parse all those complexities if they want to answer those big questions.”
Arizona State University continues its involvement at high levels across scientific fields; according to U.S. News & World Report, ASU has been named number one for innovation eight years running—a recognition based on nominations by academic leaders nationwide.
