A Super Jupiter Discovery Challenges Planet Formation Theories

When a piece of science emerges that subtly renders the textbooks from the previous ten years seem lacking, you get a certain feeling. Not exactly incorrect. Just narrower than anyone had anticipated. On February 11, 2026, a team from the University of California, San Diego published a paper in Nature Astronomy detailing what they had discovered in the atmospheres of four massive planets circling a young star known as HR 8799. Sulfur was discovered. The somewhat larger implication was that giant planets much larger than Jupiter might be forming in a manner similar to Jupiter’s, necessitating the expansion of textbooks.

HR 8799 is located in Pegasus, the cosmic equivalent of “down the block,” approximately 133 light-years away. Its inventory, not its distance, is what makes it unique. Each of the four gas giants, which orbit at a distance of roughly 15 to 70 astronomical units, has five to ten times the mass of Jupiter. In contrast, the outermost planet in our solar system, Neptune, is located roughly 30 AU from the Sun. In essence, HR 8799 is a super-sized, scaled-up version of our solar system; however, the planets are too massive and have too wide of orbits to be comfortably accommodated by classical planet formation theory.

The sulfur enters the picture at this point. Regarding the formation of giant planets, astronomers have two primary theories. The first is core accretion, a gradual, patient process in which a rocky-icy seed in the protoplanetary disk gains mass until its gravity is powerful enough to draw in surrounding gas. The archetype is Jupiter. The second is gravitational instability, in which a young disk’s turbulent patch collapses straight into a gas giant without first forming a rocky core. For years, astronomers believed that the truly massive gas giants, particularly the super-Jupiters orbiting far from their stars, formed in the same way as brown dwarfs, also known as “failed stars.” It was the more organized response.

JWST has now made it more difficult to defend that neat response by closely examining HR 8799 with its near-infrared spectrograph. Astronomers refer to sulfur as a “refractory” element because, in contrast to carbon and oxygen, it remains in solid form in the chilly outer regions of a protoplanetary disk. Sulfur enrichment in the atmosphere of a giant planet is a fairly strong indicator of core accretion. Prior to consuming gas, the planet consumed solids. Instead of building itself up like a brown dwarf, it did it like Jupiter. One of the first co-authors of the paper, Jean-Baptiste Ruffio, put it simply: even though the HR 8799 planets are five to ten times more massive than Jupiter, they most likely formed similarly to Jupiter. That was not what was anticipated.

It was difficult to extract the data. JWST was not designed with that kind of stark contrast in mind, and these planets are about 10,000 times fainter than the star they orbit. To extract the planetary signals from the starlight, Ruffio had to create new methods for data analysis. At Caltech and UCLA, Jerry Xuan iteratively improved atmospheric models until they could explain what the spectra actually revealed. Along the way, the team found hydrogen sulfide in HR 8799 c, the third planet in the system, a molecule never before found in an exoplanet atmosphere. It’s the kind of detail that indicates that instrumentation and analysis have advanced to a new level but doesn’t make headlines.

Planet formation theorists find it awkward that HR 8799 isn’t the first system to cause problems of this nature. GJ 3512b, a Jupiter-like planet circling a red dwarf with a mass ratio that defied conventional core accretion, was discovered by astronomers in 2019. Small planets were thought to reside on small stars. The memo was not received by GJ 3512b. At the time, Peter Wheatley of the University of Warwick stated that “the general impression had been that these planets just didn’t exist.” Then, a few months ago, a different team discovered four planets surrounding the red dwarf LHS 1903 that seemed to have formed sequentially rather than simultaneously, which is another subtle challenge to the simultaneous-formation models that have been the standard for decades in this field. The opposite issue is now suggested by HR 8799: the slow, accretion-based process that was meant to have a natural ceiling may still be forming giant planets that are much larger than anticipated.

Astronomers have been feeling for at least five years that the conventional models are not so much flawed as they are lacking. Quinn Konopacky, a professor at UC San Diego and co-author of the HR 8799 paper, stated it simply. This, in my opinion, demonstrates the obsolescence of earlier core accretion models.” Whether the theory is flawed is not the question. Where to draw the boundary between brown-dwarf formation and planet formation is the question. 10 Jupiter masses, 15, or 20? In the press materials, Ruffio himself questioned whether a planet could have formed like a planet even if it had thirty times the mass of Jupiter. A few years ago, that statement would have come across as provocative. It seems like someone will need to provide an answer to this open question.

The fact that so much of this moment relies on instruments that hardly existed ten years ago is what makes it truly fascinating. Not too long ago, only a few of the largest, brightest exoplanets could be directly imaged. By extracting individual molecules from atmospheres that would have been completely opaque to ground-based telescopes, JWST is currently performing detailed spectroscopy on young gas giants orbiting 133 light-years away. The science is advancing more quickly than the models can keep up, which is, in a sense, precisely what should occur as the instruments improve. The textbooks will simply need to be revised. Once more.

One discovery at a time, it’s difficult to avoid the impression that planetary science is undergoing a slow-motion paradigm shift. Nothing is altered by a single discovery. However, HR 8799 joins GJ 3512b, HD 114082 b, and LHS 1903 in an expanding list of systems that don’t quite fit into the neat categories of the 2000s. The super-Jupiters are merely the most obvious manifestation of how strange the universe has become over the past 20 years of studying exoplanets. The field will likely remain in a productive state of mild confusion for the next ten years of JWST data. That could be the best possible result for astronomers.