hydrogen sulfide in exoplanet atmospheres – Science

Scientists Discover a New Class of Molten Planets

Grant Pearson — Mon, 16 Mar 2026 10:35:24 +0000

A groundbreaking study spearheaded by researchers at the University of Oxford has uncovered an extraordinary new class of exoplanet distinguished by its capacity to store vast amounts of sulphur deep beneath a surface dominated by a permanent ocean of molten rock. This remarkable discovery, published in the prestigious journal Nature Astronomy, challenges our existing planetary classifications and broadens the horizons of planetary science beyond our Solar System.

The exoplanet in question, designated L 98-59 d, lies approximately 35 light-years from Earth, orbiting a modest red dwarf star. Its physical dimensions, about 1.6 times larger than Earth, alongside its notably low density, initially baffled astronomers. Recent measurements captured by the James Webb Space Telescope (JWST) and corroborated by terrestrial observatories indicated the unexpected presence of abundant hydrogen sulfide—a sulphur compound—in its atmosphere, a finding that defies conventional planetary models.

Traditionally, astrophysicists categorized planets like L 98-59 d as either rocky “gas dwarfs” enveloped by thick hydrogen atmospheres or as water-rich worlds dominated by oceans and ice. However, comprehensive simulations developed by an international team of scientists from the University of Oxford, Groningen, Leeds, and ETH Zurich reveal that L 98-59 d does not conform to either paradigm. Instead, it represents a novel planetary archetype defined by sulphur-rich chemistry and a molten, magma-dominated interior.

Using advanced physical and chemical modeling techniques, the research team meticulously reconstructed the evolutionary history of L 98-59 d over nearly five billion years. These simulations, integrating observational data with detailed planetary interior and atmospheric models, unveiled a planet with a mantle composed predominantly of molten silicate rock—akin to terrestrial lava—wrapped in a global magma ocean extending thousands of kilometers in depth. This magma ocean serves as a massive reservoir capable of sequestering enormous quantities of sulphur, influencing the planet’s atmospheric composition over geological timescales.

One of the key insights from this study lies in the dynamic exchange of volatile compounds between the molten interior and the overlying hydrogen-rich atmosphere. Despite the intense X-ray radiation emitted by the host star, which typically strips light atmospheres from low-mass planets, L 98-59 d has retained a dense envelope containing gases such as hydrogen sulfide (H₂S). The magma ocean acts as a stabilizing buffer, gradually releasing sulphurous volatiles into the atmosphere, maintaining chemical equilibrium across eons.

The implications of these findings suggest the existence of an entire class of sulphur-laden, magma-ocean-bearing exoplanets, challenging the simplicity of planetary classification and hinting at a far richer diversity of planetary types than previously recognized. If L 98-59 d is representative, then the Galaxy may host numerous planets where internal geochemical processes fundamentally shape atmospheric characteristics in ways not witnessed in our own Solar System.

Dr. Harrison Nicholls, the leading astrophysicist on this research, expressed enthusiasm about the ramifications of this discovery. “Our findings imply that the current frameworks astronomers use to categorize small exoplanets may be overly simplistic,” he said. “While a molten, sulphur-rich planet like L 98-59 d is unlikely to harbor life, it underscores the extraordinary variety of planetary environments awaiting discovery. This prompts the profound question: what other exotic worlds remain hidden in the cosmos?”

Central to the planet’s atmospheric composition is the interaction of ultraviolet radiation from the red dwarf star with sulphur-based gases high in the atmosphere. JWST data from 2024 revealed spectral signatures consistent with sulphur dioxide and other sulphur compounds. The research models elucidate how photochemical reactions driven by stellar UV flux produce these gases. Simultaneously, the vast magma ocean below continuously supplies these volatiles, ensuring a steady-state atmospheric composition that aligns with observational data.

From a planetary formation standpoint, simulations suggest that L 98-59 d originally possessed an abundance of volatile compounds, possibly resembling a sub-Neptune in its youth. Over billions of years, the planet cooled and contracted, shedding portions of its primordial atmosphere yet retaining its characteristic magma ocean and sulphur-rich atmosphere. This evolutionary pathway provides a new lens to interpret how rocky planets, including Earth and Mars, may have cooled from molten beginnings, but with the added complexity of volatile sulphur chemistry.

Professor Raymond Pierrehumbert, a prominent co-author, emphasized the power of computer modeling to illuminate the concealed interiors of distant worlds. “Despite our observational constraints—we can only assess a planet’s size, mass, and atmosphere remotely—these models provide a means to reconstruct a planet’s hidden past and interior processes,” he noted. This approach heralds a new era where theoretical frameworks and observational data interlace to reveal the intricate tapestries of alien planets unseen by human eyes.

Looking forward, the study’s authors highlight the promise of forthcoming missions such as Ariel and PLATO, which will yield more detailed atmospheric measurements of exoplanets. By applying machine learning algorithms to integrate these data with sophisticated interior-atmosphere models, researchers aim to map the vast diversity of worlds populating our galaxy. This pursuit not only deepens our understanding of planetary formation mechanics but also informs the search for potentially habitable environments beyond Earth.

Dr. Richard Chatterjee from the University of Leeds and Oxford remarked on the intriguing role of hydrogen sulfide—a gas familiar to us as the source of the scent of rotten eggs—in shaping planetary atmospheres in unforeseen ways. “Our simulations enable us to essentially rewind the evolutionary clock, offering insights into how this peculiar class of rocky exoplanets developed complex atmospheres dominated by sulphur compounds,” he explained. “Further observational efforts will be critical to discern whether such ‘pungent’ planets are anomalies or a common occurrence in the Universe.”

This pioneering research opens an exciting chapter in exoplanetary science by unveiling a heretofore unrecognized planetary type, defined by deep magma oceans and sulphur-rich atmospheres. As humanity’s astronomical toolkit advances, revealing ever more detailed portraits of distant planets, the cosmic menagerie of worlds continues to expand, reminding us that the Universe is more diverse and stranger than our most imaginative speculations.

Subject of Research: Evolution and characterization of a sulphur-rich molten exoplanet, L 98-59 d, including its interior magma ocean and atmospheric chemistry.

Article Title: Volatile-rich evolution of molten super-Earth L 98-59 d

News Publication Date: 16 March 2026

Web References:
DOI Link – http://dx.doi.org/10.1038/s41550-026-02815-8

Image Credits: Mark A. Garlick / markgarlick.com

Keywords

Exoplanet, L 98-59 d, sulphur-rich atmosphere, magma ocean, hydrogen sulfide, James Webb Space Telescope, planetary evolution, molten super-Earth, red dwarf star, photochemistry, planetary interior, volatile compounds

Hydrogen Sulfide Discovered in Distant Gas Giant Exoplanets for the First Time

Grant Pearson — Wed, 11 Feb 2026 22:00:33 +0000

Hydrogen sulfide, a gas notorious for its characteristic rotten egg smell, is making headlines in an unexpected context: the atmospheres of four distant gas giant planets. This groundbreaking discovery by astronomers from UCLA and the University of California, San Diego, marks the inaugural identification of hydrogen sulfide beyond our solar system. Moreover, the innovative techniques employed in this research are anticipated to significantly enhance the search for extraterrestrial life across the universe.

Gas giants such as Jupiter and Saturn are primarily composed of hydrogen and helium, alongside a dense core. Their formation is a fascinating process that unfolds in a rotating disk of dust and gas surrounding a nascent star. While typically considered large planets, gas giants can occasionally blur the lines between planets and stars. This is particularly evident when it comes to brown dwarfs, which are substellar objects that can form similarly to stars but do not reach the mass necessary for nuclear fusion. However, astronomers have recently identified brown dwarfs that fall below the 13 Jupiter mass threshold, illustrating the ambiguous boundaries that exist while classifying celestial objects of these intermediate mass ranges.

Jerry Xuan, a postdoctoral researcher at UCLA and a co-author of the paper published in Nature Astronomy, underscores the fluidity of definitions surrounding stellar and planetary formation. The established threshold for brown dwarfs is an arbitrary figure, lacking a strong foundation in our understanding of the complexities involved in such formations. The ongoing research aims to extend our grasp of these phenomena, particularly focusing on four massive gas giants revolving around the star HR 8799, situated about 133 light-years away in the constellation Pegasus.

The gas giants within this system are diverse in size, with the smallest about five times the mass of Jupiter and the largest approximately ten times as massive. These planets are situated exceptionally far from their star, with the nearest planet located at a distance 15 times greater than that between Earth and the Sun. The significant separation raises questions regarding their formation. For a considerable period, the categorization of these bodies as either planets or brown dwarfs remained uncertain, reflecting the ongoing complexity surrounding massive planetary formation.

In this landmark study, the UCLA and UCSD team utilized spectral data acquired from the James Webb Space Telescope (JWST) to detect hydrogen sulfide within the atmospheres of these distant planets. This advanced observational technique operates based on the principle that different chemical molecules absorb and emit light at specific wavelengths. By studying the light spectra, scientists can determine the elemental composition of the planets’ atmospheres, revealing the presence of specific gases like hydrogen sulfide.

Given that these planets are approximately 10,000 times fainter than their surrounding star, the research team faced the daunting challenge of extracting subtle signals from the JWST data. Jean-Baptiste Ruffio, a research scientist at UCSD and one of the paper’s co-authors, developed novel data analysis techniques to enhance the clarity of these observations. Jerry Xuan also contributed by creating intricate atmospheric models, enabling precise comparisons with the JWST spectra to ascertain the presence of sulfur in the planets’ atmospheres.

The detection of hydrogen sulfide suggests that sulfur was incorporated into the planets as solid matter during their formation. This solid matter, originating from the surrounding protoplanetary disk, combined with the extremely high temperatures in the growing planets’ cores and atmospheres, led to the evaporation of solid materials into gaseous sulfur. This mechanism is vital for understanding how gas giants accumulate elements and how their atmospheric compositions can differ dramatically from their host stars.

The ratio of sulfur to hydrogen discovered is notably higher than that found in the central star, indicating a significant divergence in composition. This unique enrichment pattern mirrors similar observations made in Jupiter and Saturn, prompting researchers to ponder whether there exists a universal process governing the formation of celestial bodies. The findings suggest that, within the environment of these distant gas giants, it is natural for them to acquire heavy elements in roughly equal proportions, showcasing an intrinsic order in the chaotic interplay of stellar formation.

Ruffio points out that the HR 8799 system stands out as the only currently imaged system with four massive gas giants. However, there exist other planetary systems housing one or two even larger companions, their formation mechanisms still shrouded in mystery. These queries have prompted astronomers to contemplate the upper limits of planetary size, igniting discussions on whether a planet could exist at 15, 20, or even 30 times the mass of Jupiter and still form as a planet rather than transitioning to brown dwarf status.

Xuan emphasizes the implications of this research for the ongoing quest to discover Earth-like exoplanets. The methodology applied—enabling researchers to visually and spectrally distinguish planets from their stars—holds great promise for studying distant exoplanets in detail as technological capabilities advance. Presently, this approach is constrained to gas giants, but, with the development of greater telescopic power and improved instruments, it is envisioned that similar techniques could be adapted for investigating terrestrial planets.

The dream of identifying an Earth analog represents the “holy grail” for exoplanet research; however, Xuan cautions that this goal may still be decades away. It is feasible that in 20 to 30 years, scientists may successfully capture the spectral signature of an Earth-like planet and begin the search for potential biosignatures, such as oxygen and ozone within its atmosphere. These future developments hinge on the continued evolution of astronomical research and technology, with the current study paving the way for understanding complex planetary systems beyond our solar system.

The research has been supported by NASA, highlighting the collaborative effort in unraveling the mysteries of our universe. As astronomers continue to peel back the layers of cosmic formation, discoveries such as these will inevitably reshape our comprehension of the cosmos and our place within it.

Subject of Research: The detection of hydrogen sulfide in distant gas giant planets’ atmospheres and its implications for planetary formation.

Article Title: The Discovery of Hydrogen Sulfide in Distant Gas Giants: Implications for the Origins of Planets

News Publication Date: October 2023

Web References: [Not available]

References: [Not available]

Image Credits: [Not available]

Keywords

Hydrogen sulfide, gas giants, exoplanets, planetary formation, James Webb Space Telescope, HR 8799, stellar formation, brown dwarfs, NASA, celestial chemistry.