A rare molecule detected in a peculiar brown dwarf – Interview with Jonathan Gagné

Several brown dwarfs, these celestial objects with masses between stars and planets, are currently being studied closely with the James Webb Space Telescope. In one of them, nicknamed “The Accident”, an international team has detected a molecule that had never been observed before: silane (SiH₄). This discovery was published in the journal Nature at the end of August.

Brown dwarfs are more massive than planets but not quite as massive as stars. Credit: NASA/JPL-Caltech.

To better understand this discovery and its significance, Jonathan Gagné, Scientific Advisor at the Planétarium de Montréal, Adjunct Professor at Université de Montréal, and member of the Trottier Institute for Research on Exoplanets (IREx), answered a few questions from IREx.

IREx: What makes this discovery special?

Jonathan: It is the first time that silane has been detected in the atmosphere of a celestial body. It is a relatively simple molecule, consisting of one silicon atom and four hydrogen atoms. Very little of it occurs naturally on Earth. It is manufactured in laboratories and industry, for example for coatings in electronics and solar panels. 

Elsewhere in the Universe, models predicted that silane should exist in the atmospheres of giant planets, both in our Solar System and beyond, as well as in brown dwarfs. But astronomers had never been able to detect it, and no one knew why. 

This detection finally gave us the answer! We realized that in atmospheres that are rich in elements heavier than hydrogen (what astronomers call “metals”), silane disappears because all the silicon atoms are locked up in silicate clouds. These clouds sink deep in the atmospheres of gas giants and brown dwarfs where we can’t see them. It was even impossible to do so on Jupiter, which we have studied up close with probes. 

WISEA J153429.75-104303.3 (or WISE 1534−1043 for short), nicknamed “The Accident”, is a brown dwarf with a truly unique chemistry, because it is extremely old: between 10 and 13 billion years. Over cosmic time, elements like carbon, nitrogen, and oxygen were formed in the cores of stars, so the planets and stars that formed more recently contain higher proportions of these elements. By observing “The Accident”, we were finally able to detect silane, because silicon atoms remained free in its atmosphere: the oxygen that would otherwise trap them into silicate clouds is too scarce to completely deplete the silicon.

IREx: Where does the nickname The Accident come from? 

Jonathan: This brown dwarf was discovered by Dan Caselden, a citizen scientist taking part in the Backyard Worlds project. He noticed a strange-looking object moving rapidly while looking at an image of the sky taken by the NEOWISE space telescope (for an entirely different reason!) Because the discovery was fortuitous, the team nicknamed it The Accident. Since then, we’ve learned that it is one of the strangest brown dwarfs ever observed, with a chemistry completely unlike the others, so the name is fitting!

IREx: How did you learn more about this unique object? 

Jonathan: After the initial discovery in 2020, the Backyard Worlds team worked to better understand this fascinating object, using observations from the Hubble and Spitzer space telescopes. More recently, my colleague Jackie Faherty at the American Museum of Natural History obtained observing time with the James Webb Space Telescope, which finally allowed us to probe its atmosphere.

IREx: What was your role in this project? 

Jonathan: My main contribution was to use Webb’s observations to calculate the brown dwarf’s motion in our Galaxy. Its fast velocity helped us solidify our understanding that it is indeed extremely old. It formed at a time when the Universe contained far fewer heavy elements than it does today.

IREx: What does this discovery mean for the future? 

Jonathan: It shows that cloud formation in atmospheres can radically transform the chemistry we observe. This helps explain why some molecules predicted by our models are missing in the atmospheres of planets in the Solar System. 

We still have much to learn: further Webb observations are underway, which may reveal whether faint clouds are present in this atmosphere, or none at all! Each discovery of this kind brings us closer to a global understanding of planets and distant worlds.

IREx: Why are you personally interested in studying brown dwarfs?

 Jonathan: Because it’s exciting to learn more about everything that exists in the Universe! Studying these objects also helps us better understand our own gas giants, Jupiter and Saturn, as well as giant exoplanets in general. Brown dwarfs are not exactly planets, but they resemble them in many ways. It’s much easier to study their atmospheres, since they’re not outshone by a nearby star. We now know of about 3,000 brown dwarfs, with complex gaseous atmospheres and variable clouds. Their diverse properties make brown dwarfs perfect laboratories for testing our physical models under all kinds of conditions.

​​Note: This interview, based on a written Q&A with Jonathan Gagné and on NASA’s press release, has been edited for clarity.

Learn more

The paper Silicate precursor silane detected in cold low-metallicity brown dwarf was published in Nature on August 20, 2025. In addition to lead author Jackie Faherty of the American Museum of Natural History and Jonathan Gagné of IREx, the team includes 29 co-authors from the United States, the United Kingdom, and Europe.

Contacts

Media contact
Marie-Eve Naud
Education and Communications Coordinator
Trottier Institute for Research on Exoplanets (IREx), Université de Montréal
514-279-3222
marie-eve.naud@umontreal.ca

Scientific contact
Jonathan Gagné
Scientific Advisor, Planétarium de Montréal, Espace pour la vie
Adjunct Professor, Université de Montréal
jonathan.gagne@montreal.ca 

Links

• The scientific paper in Nature
• NASA’s news release
• Espace pour la vie news release

Lead author Jackie Faherty presented the 2025 Grande conférence de l’IREx (available on YouTube)