JWST Detects Sulfur in Super-Jupiters

The detection of sulfur occurred in the star system HR 8799, about 133 light-years away in the constellation Pegasus. The system is young, at only 30 million years old, and hosts four massive "super-Jupiter" planets, each five to 10 times the mass of our own Jupiter. These planets orbit incredibly far from their star, at distances of 15 to 70 astronomical units (AU)—for comparison, Jupiter is only about 5 AU from our sun. JWST's instruments found hydrogen sulfide (H₂S) in the atmosphere of the third planet, HR 8799 c, and it's believed to be present on the other inner planets as well. This is a crucial clue because, in the cold, outer regions of a planet-forming disk, sulfur exists as a solid. Its presence in the atmosphere implies the planet must have formed by swallowing solid materials, a hallmark of the "core accretion" model where planets are built up piece by piece. The alternative, the "gravitational instability" or "failed-star" model, suggests giant planets at such large orbits form rapidly when a cloud of gas collapses under its own gravity. Planets formed this way are expected to have a chemical composition similar to their star. However, the HR 8799 planets have higher amounts of heavy elements like carbon, oxygen, and now sulfur, compared to their star, strengthening the case for their planet-like, core-accretion origins. Separately, the potential biosignature on K2-18b is dimethyl sulfide (DMS), a molecule that on Earth is overwhelmingly produced by life, particularly marine phytoplankton. The exoplanet K2-18b is a "super-Earth," 8.6 times Earth's mass, located 124 light-years away, and orbits within its star's habitable zone where liquid water could exist. Previous JWST observations had already identified methane and carbon dioxide on K2-18b, suggesting it could be a "Hycean" world—a planet with a liquid water ocean under a hydrogen-rich atmosphere. The DMS signal, while exciting, is reported with a 3-sigma level of statistical confidence, which is below the 5-sigma threshold typically required for a definitive scientific discovery. More observation time is needed for confirmation. The comparison to Mars relates to the detection of complex organic molecules by the Curiosity rover. In 2025, scientists analyzing a 3.7-billion-year-old rock sample from Gale Crater found long-chain molecules like decane and undecane. These are believed to be fragments of even larger molecules called fatty acids, which are considered universal products of biochemistry. While fatty acids can be formed by non-biological processes, their discovery proves that the building blocks for life could have existed on ancient Mars and, crucially, that organic signatures can be preserved in Martian rock for billions of years. This lends hope that remnants of life, if it ever emerged, might still be detectable on the Red Planet.