In the vast expanse of the universe, astronomers often encounter cosmic puzzles that defy simple explanations. One such long-standing mystery concerns the atmospheres of gas giants like Jupiter and Saturn. Why do they lack silicon, one of the most abundant elements in the universe? The answer to this question, it seems, has come from an unexpected direction – the study of an unusual celestial body that, due to its strange nature and accidental discovery, was nicknamed "The Accident".

A new study, relying on the incredible capabilities of the James Webb Space Telescope, has shed new light on the chemical processes hidden deep within the atmospheres of these planets, as well as thousands of other worlds beyond our Solar System. At the heart of the story is a molecule that scientists have long sought but, until now, had failed to find – silane.

A chance discovery that changed everything

"The Accident," officially named WISEA J153429.75-104303.3, is a brown dwarf, a fascinating celestial body that represents a transitional form between the largest planets and the smallest stars. Brown dwarfs are more massive than Jupiter but not massive enough to ignite the nuclear fusion of hydrogen in their core, the process that gives stars their shine. Yet, even in the category of these "failed stars," "The Accident" stands out as an exceptionally unusual specimen.

This object possesses a confusing combination of characteristics; some are typical of very young brown dwarfs, while others are seen only in extremely old ones. Precisely because of this unusual nature, it eluded standard detection methods for years. It was discovered only five years ago, not by a professional astronomer, but thanks to the enthusiasm of a citizen scientist. Dan Caselden, a participant in the Backyard Worlds: Planet 9 project, noticed the faint movement of this object while reviewing archival data from NASA's NEOWISE (Near-Earth Object Wide-field Infrared Survey Explorer) mission. This project allows volunteers from around the world to analyze vast amounts of data and help discover new worlds in our cosmic neighborhood.

"The Accident" is so faint and spectrally strange that scientists had to use the most powerful space observatory ever built, the James Webb Telescope, to peer into its atmosphere. The analysis of the light passing through the atmosphere of this brown dwarf revealed several surprises, but one was particularly important. Among the chemical signatures, the team noticed traces of a molecule they initially could not identify. A more detailed analysis confirmed it to be silane ($SiH_4$), a simple molecule consisting of a single silicon atom and four hydrogen atoms.

The ghost of a molecule: Why is finding silane a great success?

The discovery of silane is monumental. For decades, scientists have theorized that this molecule should exist not only in the atmospheres of brown dwarfs but also in the upper layers of the atmospheres of the gas giants in our Solar System. Yet, despite numerous searches, it had never been detected – until now. "The Accident" became the first object of its kind in whose atmosphere the existence of silane has been unequivocally confirmed.

The scientific community is quite certain that silicon exists in Jupiter's and Saturn's atmospheres, but they believe it is hidden from our view. The dominant theory suggests that silicon, in the presence of oxygen, binds very easily to form silicate compounds, such as quartz. On hot gas giants, these silicates can form clouds, similar to sandstorms on Earth. On colder gas giants, like Jupiter and Saturn, these heavy silicate clouds sink deep into the atmosphere, far below the lighter layers of ammonia and water vapor clouds. They are at such great depths that they are invisible even to the spacecraft that have studied these planets up close.

However, some researchers hypothesized that lighter silicon molecules, like silane, should remain in the upper layers of the atmosphere, like traces of flour on a baker's table. The fact that such molecules have not been found anywhere except in this one, extremely unusual brown dwarf, suggests something crucial about the chemistry that occurs in these environments. "Sometimes you need the extreme objects to understand what's happening in the average ones," said Jacqueline Faherty, a researcher at the American Museum of Natural History in New York and the lead author of the study published in early September in the prestigious journal Nature.

A relic from the dawn of the universe

To understand why "The Accident" has silane and other objects do not, we must go far back in time. Located about 50 light-years from Earth, this brown dwarf likely formed 10 to 12 billion years ago. Given that the universe itself is about 13.8 billion years old, "The Accident" is one of the oldest brown dwarfs ever discovered – a true cosmic relic.

At the time this object was forming, the universe was chemically very poor. It consisted almost exclusively of hydrogen and helium, with only negligible amounts of heavier elements, including silicon. Elements like carbon, nitrogen, and oxygen, crucial for the chemistry as we know it, are created in the cores of stars and dispersed throughout the universe only after their death. Therefore, planets and stars that formed later, like our Sun, Jupiter, and Saturn, possess significantly more of these elements.

Observations from the Webb telescope confirm that silane can indeed form in the atmospheres of brown dwarfs and planets. Its absence in other, younger objects strongly suggests that when oxygen is available, it binds with silicon with exceptional ease and efficiency. In this process, oxygen "gobbles up" all available silicon, leaving almost nothing to bind with hydrogen and form silane.

So why does "The Accident" have silane? The study's authors hypothesize that the reason is precisely its age. In the early universe, when this ancient brown dwarf was formed, there was far less oxygen. Due to this lack, silicon had nothing to form silicates with. Instead, it bonded with the most available element – hydrogen – and thus silane was formed, a molecule that has been preserved in its atmosphere for billions of years.

Broader cosmic significance

This discovery has implications that extend far beyond understanding Jupiter and Saturn. Brown dwarfs are often easier to study than exoplanets, the gas giants that orbit other stars. The light from a distant planet is usually overshadowed by the glare of its parent star, while brown dwarfs mostly travel through space alone, making them ideal natural laboratories for studying planetary atmospheres.

"We didn't set out on these observations with the intention of solving the mystery of Jupiter and Saturn," said Peter Eisenhardt of NASA's Jet Propulsion Laboratory (JPL), a project scientist for the WISE mission. "We wanted to find out why this brown dwarf is so strange, but we didn't expect silane. The universe constantly surprises us."

The lessons learned from studying objects like "The Accident" are applicable to all kinds of planets, including those outside our Solar System that might show signs of habitability. Although it is important to emphasize that this is not about a search for life, the methodology is key. "To be clear, we are not finding life on brown dwarfs," Faherty clarified. "But at a higher level, by studying all this diversity and complexity in planetary atmospheres, we are preparing the scientists who will one day have to do these kinds of chemical analyses for rocky, Earth-like planets. It might not be specifically about silicon, but they will get data that is complicated, confusing, and doesn't fit existing models, just like us. They will have to dissect all that complexity if they want to answer the big questions."