Ancient brown dwarf reveals cloud chemistry secrets

Deep in space, an ancient brown dwarf nicknamed "The Accident" has revealed the first-ever detection of a molecule that scientists have been searching for in planetary atmospheres for decades.

This discovery, now published in Nature, not only explains why silicon remains hidden in Jupiter and Saturn's atmospheres, but also opens a window into how the chemistry of our universe has evolved over billions of years, showing us that sometimes the most unexpected finds yield the greatest scientific breakthroughs.

For the first time ever, astronomers identified silane, a simple molecule made of silicon bonded with four hydrogen atoms, in the atmosphere of a celestial object. This discovery is significant because planetary scientists have predicted silane should exist in gas giants and it plays an important role in cloud formation, until now though, it has eluded detection on Jupiter or Saturn.

The brown dwarf, known as "The Accident" is located about 50 light years away in the constellation Libra, likely formed 10 to 12 billion years ago, making it one of the oldest brown dwarfs ever discovered. Brown dwarfs are fascinating objects which are too massive to be considered planets but not massive enough to sustain nuclear fusion like stars. It was discovered accidentally in 2020 (hence its name) by a citizen scientist participating in the Backyard Worlds, Planet 9 project.

The investigation began when astronomer Sandy Leggett used the Gemini South telescope in Chile to obtain near-infrared images of The Accident. The Gemini South telescope is the only ground-based telescope able to detect this extremely faint object and it enabled further observations with NASA's James Webb Space Telescope, whose unprecedented sensitivity revealed the silane signature.

The discovery explains a long-standing mystery about silicon in planetary atmospheres. Scientists are fairly confident that silicon exists in Jupiter's and Saturn's atmospheres but it has until now, never been detected. The models suggest that in the gas giants we see today, silicon bonds with readily available oxygen. This creates heavier molecules that sink deep below surface layers where telescopes cannot detect them.

However, The Accident formed when the universe was much younger and contained far less oxygen. With far less oxygen present when the brown dwarf formed, available silicon bonded with hydrogen instead, resulting in silane. This was much lighter, was unable to sink and is therefore readily detectable.

This research demonstrates how studying extreme objects helps scientists understand average ones. The findings confirm theories about cloud formation in gas giants and provide crucial insights into how the timing of planetary formation affects atmospheric composition. Researchers plan to use Webb and other instruments to search for silane in additional brown dwarfs and exoplanets, potentially revolutionizing our understanding of atmospheric chemistry across the universe.