James Webb Space Telescope studies a 'failed star' named 'The Accident' to solve an old mystery of Jupiter and Saturn

Using the James Webb Space Telescope (JWST), astronomers have investigated a "failed star," or brown dwarf, nicknamed "The Accident." Their results may help solve a long-standing mystery surrounding the solar system's gas giants, Jupiter and Saturn.

Brown dwarfs get their unfortunate label of "failed stars" due to the fact that they form from collapsing clouds of gas and dust like stars, but they fail to gather enough matter to achieve the mass needed to trigger the nuclear fusion of hydrogen to helium in their cores, the process that defines what a star is. Brown dwarfs have masses between 13 and 80 times the mass of Jupiter, or 0.013 and 0.08 times the mass of the sun.

Yet even among these strange, hard-to-classify celestial objects, The Accident, located 50 light-years from Earth and believed to be between 10 billion and 12 billion years old, stands out. It is one of the oldest brown dwarfs ever seen, and has some features that have previously only been seen in young brown dwarfs. It also exhibits characteristics that have only previously been associated with ancient failed stars. These paradoxical features led to The Accident escaping detection until it was discovered by chance in 2020 by NASA's now-retired Near-Earth Object Wide-field Infrared Survey Explorer (NEOWISE).

The fact that The Accident is faint and unusual has led scientists to prioritize its study with the most powerful space telescope available, the James Webb Space Telescope. This led to the discovery of an unexpected molecule that initially defied identification, but was eventually determined to be a simple one called silane, formed when silicon and hydrogen bond.

Here's where Jupiter and Saturn come in.

For years, astronomers have expected to find silane in the solar system's gas giants. This molecule has also been missing around extrasolar planet, or "exoplanet," gas giants around other stars, and from other brown dwarfs.

Scientists are fairly certain silicon does exist in Jupiter and Saturn, but that it "hides" by binding with oxygen to create oxides like quartz. These oxides then seed clouds on hot gas giants that resemble dust storms on Earth, while on cooler gas giants like Jupiter and Saturn, they sink below the lighter upper atmospheric layers of water vapor and ammonia clouds. That results in silicon sinking deep into the atmospheres of Jupiter and Saturn and thus avoiding detection by spacecraft that have studied those planets up close.

However, even if this is the case, scientists have suggested light molecules of silicon, like silane, should be found in the upper atmospheres of gas giants and brown dwarfs.

As of now, The Accident is the first and only such object where this molecule has been identified. This could tell scientists something important about the conditions and chemistry of different worlds.

"Sometimes it's the extreme objects that help us understand what’s happening in the average ones," team leader Jacqueline Faherty, a researcher at the American Museum of Natural History in New York City, said in a statement.

The detection of silane around The Accident's atmosphere suggests this silicon molecule does indeed form in brown dwarfs and planetary atmospheres. However, the team thinks that when oxygen is available, it bonds with silicon at such a rapid rate that none is left to bind with hydrogen and form silane.

The team theorizes that silane is present in The Accident because during the time period in which it formed, at least 10 billion years ago, the universe was saturated with much less oxygen than in later epochs. That means silicon would have been free to bind with hydrogen and form silane.

"We weren't looking to solve a mystery about Jupiter and Saturn with these observations," Peter Eisenhardt, study team member and a project scientist at NEOWISE, said in the statement. "A brown dwarf is a ball of gas like a star, but without an internal fusion reactor; it gets cooler and cooler, with an atmosphere like that of gas giant planets. We wanted to see why this brown dwarf is so odd, but we weren't expecting silane.

"The universe continues to surprise us."

The research demonstrates the usefulness of brown dwarfs, which wander the galaxy in isolation, as proxies for gas giant exoplanets that can be obscured by the light from the parent stars they orbit.

Indeed, brown dwarfs could also help investigate exoplanet habitability conditions despite not being able to support life themselves.

"To be clear, we're not finding life on brown dwarfs," Faherty explained. "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."

The team's research was published on Sept. 4 in the journal Nature.