An unusual cosmic object is offering scientists a deeper understanding of the chemistry hidden in the atmospheres of Jupiter and Saturn, as well as those of distant exoplanets. Researchers have long puzzled over why silicon, one of the most abundant elements in the universe, has largely gone undetected in the atmospheres of gas giants, including Jupiter and Saturn. A groundbreaking study utilizing observations from NASA’s James Webb Space Telescope provides valuable insights into this mystery.
The study centers around a peculiar cosmic object dubbed “The Accident,” a brown dwarf discovered serendipitously in 2020. This object, which is neither a planet nor a star, has a bewildering array of physical characteristics that have made it difficult to classify. Interestingly, these features are reminiscent of both young and ancient brown dwarfs, leading to its initial oversight by traditional detection methods. The Accident was identified by a citizen scientist participating in the Backyard Worlds: Planet 9 project, which encourages global participation in discovering new celestial bodies using data from NASA’s now-retired NEOWISE (Near-Earth Object Wide-field Infrared Survey Explorer) mission.
Due to its faintness and unusual attributes, The Accident required the advanced technology of NASA's James Webb Space Telescope for atmospheric analysis. Among the several surprises that emerged from the study, researchers found evidence of a previously unidentified molecule, which turned out to be a simple silicon compound known as silane (SiH4). This discovery is significant because scientists have long theorized the existence of silane not only in our solar system's gas giants but also in the atmospheres of numerous brown dwarfs and gas giants orbiting other stars.
The research indicates that while scientists are fairly certain that silicon exists in the atmospheres of Jupiter and Saturn, it remains largely hidden. In these gas giants, silicon bonds with oxygen to form oxides like quartz, which can seed clouds resembling dust storms on Earth. In cooler gas giants such as Jupiter and Saturn, these clouds tend to sink far beneath lighter layers of water vapor and ammonia clouds, making any silicon-containing molecules elusive, even for spacecraft that have closely studied these planets.
Some researchers speculate that lighter silicon molecules, such as silane, should be present higher in the atmospheric layers, akin to traces of flour left on a baker's table. The absence of these molecules in most other brown dwarfs and gas giants suggests unique chemical processes are occurring in these environments.
Located approximately 50 light-years from Earth, The Accident is believed to have formed between 10 billion and 12 billion years ago, making it one of the oldest brown dwarfs discovered to date. At the time of its formation, the universe was predominantly composed of hydrogen and helium, with only trace amounts of other elements, including silicon. Over billions of years, elements like carbon, nitrogen, and oxygen were synthesized in stars, leading to planets and stars formed later containing higher quantities of these elements.
Observations from the James Webb Space Telescope confirm that silane can indeed form in the atmospheres of brown dwarfs and gas giants. The apparent absence of silane in other brown dwarfs and gas giants implies that when oxygen is abundant, it readily bonds with silicon, leaving little to no silicon available to bond with hydrogen and form silane. The study authors propose that the lower levels of oxygen present in the atmosphere of The Accident allowed for silicon to bond with hydrogen, resulting in the formation of silane.
“We weren’t specifically looking to solve a mystery about Jupiter and Saturn with these observations,” noted Peter Eisenhardt, project scientist for the WISE (Wide-field Infrared Survey Explorer) mission, which was subsequently repurposed as NEOWISE. He elaborated that brown dwarfs serve as gas-like entities similar to stars but lack an internal fusion reactor, resulting in a cooler atmosphere akin to that of gas giant planets. While researchers initially sought to understand why The Accident is so distinctive, the unexpected discovery of silane underscores the universe's capacity to surprise.
Brown dwarfs, like The Accident, are often easier to study than distant gas giant exoplanets, as the light from a far-off planet is typically overshadowed by the star it orbits. The insights gained from studying these unique objects extend to a wider array of planetary bodies, including those outside our solar system that may harbor potential signs of habitability.
“To clarify, we are not discovering life on brown dwarfs,” Faherty emphasizes. “However, by examining the diversity and complexity in planetary atmospheres, we are preparing scientists for future endeavors that will involve chemical analyses of rocky, potentially Earth-like planets. While it may not specifically relate to silicon, they will encounter intricate and perplexing data that defies their models, much like what we are experiencing now.”
The Wide-field Infrared Survey Explorer (WISE), managed by a division of Caltech, was operated under NASA’s Science Mission Directorate. The mission was selected as part of NASA’s Explorers Program, which is managed by the Goddard Space Flight Center in Greenbelt, Maryland. The NEOWISE mission, a collaboration between JPL and the University of Arizona in Tucson, was supported by NASA’s Planetary Defense Coordination Office.
The James Webb Space Telescope stands as the premier space science observatory globally, representing an international effort led by NASA alongside its partners, the European Space Agency (ESA), and the Canadian Space Agency (CSA). To learn more about Webb, visit: NASA's official webpage.
For further inquiries, contact:
Calla Cofield
Jet Propulsion Laboratory, Pasadena, Calif.
626-808-2469
calla.e.cofield@jpl.nasa.gov
Christine Pulliam
Space Telescope Science Institute, Baltimore, Md.
cpulliam@stsci.edi
