Astronomers have discovered phosphine gas in the atmosphere of the brown dwarf Wolf 1130C using the James Webb Space Telescope. This finding, led by researchers at the University of California San Diego, challenges expectations as phosphine has been absent in similar objects. The detection could reveal insights into phosphorus chemistry in low-metal environments.
Phosphine (PH3), a highly toxic and explosive gas that bonds phosphorus with hydrogen, is one of the essential elements for life on Earth and a potential biosignature for anaerobic life. It occurs naturally in the atmospheres of Jupiter and Saturn and from decaying organic material on Earth, but has been elusive in exoplanets and brown dwarfs despite theoretical predictions.
A team led by University of California San Diego Professor of Astronomy and Astrophysics Adam Burgasser detected phosphine in the atmosphere of the cool, ancient brown dwarf Wolf 1130C. The findings were published in the journal Science in 2025 (DOI: 10.1126/science.adu0401). Using the James Webb Space Telescope (JWST), the first instrument capable of detailed analysis of such dim, low-temperature objects, the researchers observed a strong infrared signal from phosphine.
Wolf 1130C is part of a three-star system 54 light-years away in the constellation Cygnus, orbiting a binary pair: a cool red star (Wolf 1130A) and a dense white dwarf (Wolf 1130B). This brown dwarf, sometimes called a 'failed star,' has far fewer metals—elements heavier than hydrogen and helium—than the Sun, making it a key laboratory for primitive cosmic chemistry.
The surprise lies in phosphine's absence from other brown dwarfs and gas giant exoplanets observed by JWST. "Prior to JWST, phosphine was expected to be abundant in exoplanet and brown dwarf atmospheres, following theoretical predictions based on the turbulent mixing we know exists in these sources," said co-author Sam Beiler, a postdoctoral scholar at Trinity College Dublin. "Every observation we've obtained with JWST has challenged the theoretical predictions—that is until we observed Wolf 1130C."
Assistant Professor Eileen Gonzales from San Francisco State University used atmospheric retrieval modeling to confirm phosphine's abundance at about 100 parts per billion. One hypothesis attributes this to the metal-depleted atmosphere lacking sufficient oxygen to bind phosphorus, allowing it to form phosphine with abundant hydrogen. Another suggests local production from the white dwarf Wolf 1130B through past nova events, which could enrich surroundings with phosphorus.
The team's program, Arcana of the Ancients, targets old, metal-poor brown dwarfs to test atmospheric chemistry. "Understanding the problem with phosphine was one of our first goals," Burgasser noted. Upcoming JWST observations of similar objects will test these ideas. This work, supported by NASA/STScI (NAS 5-03127 and AR-2232) and the Heising-Simons Foundation, could inform phosphorus origins in the galaxy and its role in planetary atmospheres, aiding searches for life beyond Earth.