Astronomers using NASA/ESA/CSA’s James Webb Space Telescope have for the first time detected hydrogen sulfide gas in the atmospheres of three gas giant exoplanets orbiting HR 8799, a 30-million-year-old star located in the constellation Pegasus. They discovered that the sulfur must have come from solid material in the planet’s birth disk.

HR8799 It is located about 129 light years from us in the constellation Pegasus.

The star has a huge debris disk and four superjupiters (HR 8799b, c, d, and e).

The smallest planet is five times heavier than Jupiter, and the largest is more than 10 times heavier.

Planets are far from their stars, with the closest planet being 15 times the distance from Earth to the Sun.

Unlike most exoplanet discoveries, which are inferred from analysis of data, these worlds directly visible through a ground-based telescope.

“HR 8799 is somewhat unique because it is the only imaged star system containing four gas giant planets so far, but there are other systems known to have one or two even larger companion stars, the formation of which is still unknown,” said Dr. Jean-Baptiste Ruffio, an astronomer at the University of California, San Diego.

Using Webb’s unprecedented sensitivity, Rufio and his colleagues made detailed measurements of the chemical composition of three planets orbiting HR 8799: HR 8799c, d, and e.

Because planets are about 10,000 times fainter than stars, researchers developed new data analysis techniques to extract weak signals from the Webb data.

“Carbon and oxygen on these planets have been studied in the past with observations from Earth, but they could come from ice, solids, or gas in the disk, so they’re not a good sign of solid material,” said Dr. Jerry Xuan, a postdoctoral researcher at the University of California, Los Angeles and the California Institute of Technology.

“But sulfur is unique because, far from the star, these planets should have sulfur in solid form.”

“It is impossible for these planets to accrete sulfur as a gas.”

The discovery of hydrogen sulfide means that sulfur was accreted, or accumulated, in solid form from solids that were already present in the disk around the star from which the planet was born.

These solids were swallowed up as the planet formed, and the young planet’s core and atmosphere were so hot that the solids evaporated into the sulfur gas that exists today.

The sulfur-to-hydrogen and carbon-to-oxygen-to-hydrogen ratios are much higher than those found in stars. Therefore, the composition of a planet should be quite different from that of a star.

The same puzzling pattern of uniform enrichment of heavy elements is also seen on Jupiter and Saturn.

“Jupiter’s uniform enrichment of carbon, oxygen, sulfur, and nitrogen is not easy to explain, but the fact that we are observing this in another star system suggests that something universal is happening in planet formation: It is quite natural for planets to accrete all heavy elements in roughly equal proportions,” Dr. Xuan said.

The authors say the discovery could help in the search for Earth-like exoplanets.

“The technique applied here allows researchers to visually and spectrally separate planets from stars, which will help us study exoplanets far from Earth in detail,” Dr. Xuan said.

“This method is still limited to studying gas giant planets, but eventually, as telescopes get bigger and instruments improve, scientists will be able to apply this type of technique to studying Earth-like planets.”

“Finding an Earth analog is the holy grail for exoplanet exploration, but it will likely take decades to achieve it.”

“But perhaps within 20 to 30 years, we will have the first spectra of an Earth-like planet and explore biological signatures such as oxygen and ozone in its atmosphere.”

of findings Published in the Journal on February 9, 2026 natural astronomy.

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JB. Ruffio others. Jupiter-like homogeneous metal enrichment in a system of multiple giant exoplanets. Nat Astronpublished online on February 9, 2026. doi: 10.1038/s41550-026-02783-z