For the first time, astronomers utilizing NASA/ESA/CSA’s James Webb Space Telescope have detected hydrogen sulfide gas in the atmospheres of three gas giant exoplanets orbiting the star HR 8799, located in the Pegasus constellation and approximately 30 million years old. This significant finding indicates that the sulfur originated from solid materials in the protoplanetary disk where the planets formed.

HR 8799 lies about 129 light-years away from Earth and hosts a substantial debris disk alongside four super-Jupiter planets (HR 8799b, c, d, and e).

The smallest of these gas giants is five times the mass of Jupiter, while the largest exceeds ten times Jupiter’s mass.

These exoplanets reside far from their star, with the nearest planet being situated 15 times farther from its star than Earth is from the Sun.

Unlike many exoplanets discovered through indirect data analysis, the planets in the HR 8799 system can be directly observed using ground-based telescopes.

“HR 8799 is unique as the only imaged stellar system containing four gas giant planets, although other systems have one or two larger companion stars with formation processes yet to be understood,” explained Dr. Jean-Baptiste Ruffio, an astronomer at the University of California, San Diego.

Utilizing Webb’s unprecedented sensitivity, Dr. Ruffio and colleagues conducted detailed studies of the chemical compositions of the planets HR 8799c, d, and e.

Due to the faintness of these planets—approximately 10,000 times dimmer than their host star—the researchers developed innovative data analysis techniques to isolate weak signals in the Webb data.

“Prior studies of carbon and oxygen on these planets, conducted from Earth, could originate from ice, solids, or gas in the disk, making them unreliable indicators of solid material,” noted Dr. Jerry Xuan, a postdoctoral researcher at UCLA and Caltech.

“In contrast, sulfur is distinctive because, away from the star, these planets should harbor sulfur in solid form.”

“It’s impossible for these planets to accumulate sulfur in gaseous form.”

The identification of hydrogen sulfide indicates that sulfur was gathered in solid form from materials that existed in the disk surrounding the star during the planets’ formation. These solids were assimilated as the planet formed, and the intense heat of the young planet’s core and atmosphere caused them to vaporize into the sulfur gas present today.

Notably, the sulfur-to-hydrogen and carbon-to-oxygen-to-hydrogen ratios on these planets are significantly higher than those found in stars, hinting at a distinct planetary composition.

This puzzling consistency in the enrichment of heavy elements is also observed in Jupiter and Saturn.

“The uniform enhancement of carbon, oxygen, sulfur, and nitrogen in Jupiter is complex, but observing this in another star system suggests a universal trend in planet formation, where planets naturally integrate heavy elements in nearly equal proportions,” Dr. Xuan commented.

The findings could advance the search for Earth-like exoplanets.

“The techniques used here allow for the optical and spectral separation of planets from stars, enabling detailed studies of exoplanets located far from Earth,” Dr. Xuan stated.

“While currently limited to gas giants, as telescope technology and instruments improve, scientists aim to apply these methods to Earth-like planets.”

“Locating an Earth analog is the ultimate goal of exoplanet research; however, achieving this may take decades.”

“Nevertheless, within the next 20 to 30 years, we might obtain the first spectra of an Earth-like planet, allowing us to investigate biological markers such as oxygen and ozone in its atmosphere.”

Findings detailed in the Journal of Natural Astronomy on February 9, 2026.

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J.B. Ruffio et al. “Jupiter-like homogeneous metal enrichment in a system of multiple giant exoplanets,” Nat Astron published online on February 9, 2026. doi: 10.1038/s41550-026-02783-z