9 Sept 2025-------------- Noirlab 2526

 

In the first discovery of its kind, astronomers have found silane in the atmosphere of an ancient brown dwarf nicknamed The Accident. This molecule plays an important role in the formation of clouds in gas giant atmospheres, but for decades it has eluded detection in planets like Jupiter and Saturn. The discovery was made possible with complementary observations from the U.S. National Science Foundation-funded Gemini South telescope in Chile and NASA’s James Webb Space Telescope.

Brown dwarfs are peculiar objects that are too massive to be considered planets, but not massive enough to sustain nuclear fusion like a star. Among this curious class of objects, a brown dwarf nicknamed The Accident stands out for its unique mix of physical features, exhibiting characteristics previously seen only in warm, young brown dwarfs and others previously seen only in cool, ancient ones.

The Accident’s properties are highly unusual compared to all other known stars and brown dwarfs, so it slipped past typical detection methods. It was discovered accidentally in 2020 by a citizen scientist participating in the Backyard Worlds: Planet 9 citizen science project. Its strange light profile piqued the interest of astronomers, so they turned to two of the world’s most powerful ground- and space-based telescopes to peer into its atmosphere and better understand its nature and composition.

The investigation began with NSF NOIRLab astronomer Sandy Leggett obtaining near-infrared images of The Accident using the Gemini South telescope in Chile, one half of the International Gemini Observatory, funded in part by the U.S. National Science Foundation (NSF) and operated by NSF NOIRLab. This laid the groundwork for further investigations, led by NOIRLab astronomer Aaron Meisner, using NASA’s James Webb Space Telescope.

“The Accident is extremely faint, and Gemini South remains the only ground-based telescope that’s so far been able to detect it,” says Meisner, co-author on the paper presenting these results in Nature. “The Gemini detection set the stage for observations with JWST by allowing us to estimate the exposure time we would need to probe this enigmatic object’s deep atmospheric layers and get useful near-infrared data about its composition.”

The observations from Webb revealed a surprise. In The Accident’s atmosphere, the team found a conclusive signature of the chemical silane — silicon bonded with four hydrogen atoms. Planetary scientists have long predicted that this molecule exists in gas giants and that it plays an important role in the formation of clouds within their atmospheres. Despite decades of searching, it eluded detection in the atmospheres of our Solar System’s gas giants, Jupiter and Saturn, as well as the thousands of atmospheres scientists have studied on brown dwarfs and gas giants around other stars.

This marks the first discovery of silane in any brown dwarf, exoplanet, or Solar System object. The fact that this molecule hasn’t been detected anywhere except in a single, peculiar brown dwarf suggests something about the chemistry occurring in such ancient environments.

“Sometimes it’s the extreme objects that help us understand what’s happening in the average ones,” says Jackie Faherty, a researcher at the American Museum of Natural History in New York City and lead author on the paper.

Located about 50 light-years from Earth, The Accident likely formed 10–12 billion years ago, making it one of the oldest brown dwarfs ever discovered. The Universe is nearly 14 billion years old, meaning that The Accident formed at a time when the cosmos contained mostly hydrogen and helium, with trace amounts of other elements, including silicon. Over eons, elements like carbon, nitrogen, and oxygen formed in the cores of stars, meaning that planets and stars that formed more recently possess more of those elements.

The presence of silane in The Accident’s atmosphere suggests that, in very old objects, silicon can bond with hydrogen to form a light molecule that can reach the upper layers of a gas giant’s atmosphere. But in objects that formed more recently, like Jupiter and Saturn, the silicon bonds with the more readily available oxygen, creating heavier molecules that sink deep below the surface layers of the atmosphere, where they are undetectable by our telescopes.

The evidence uncovered in The Accident’s atmosphere confirms astronomers’ understanding of how clouds on gas giants form, and offers critical insight into how primordial formation can impact the composition of a planet’s atmosphere. Additionally, it reveals how a world formed billions of years ago can look drastically different than a world formed during the dawn of our Solar System.

 

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(B) What is a Brown Dwarf?