Astronomers Reveal Super Jupiters' Formation Process

JWST data provides clues about how massive planets far from their stars form.

Published on Feb. 10, 2026

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Astronomers have used data from the James Webb Space Telescope to study the HR 8799 star system, which contains four super Jupiter-sized planets. Their findings suggest that these massive, distant planets likely formed through a process similar to how Jupiter formed, rather than through a different mechanism called gravitational instability.

Why it matters

Understanding how super Jupiters form provides insights into planet formation processes beyond our own solar system. The discovery that these distant, massive planets can still form via core accretion, like Jupiter, expands the known limits of where this planetary formation mechanism can occur.

The details

The researchers analyzed spectral data from JWST and detected the presence of sulfur in the atmosphere of the third planet, HR 8799 c. This indicates the planet likely formed via core accretion, as sulfur-containing molecules would be solid in a planet-forming disk, rather than gaseous. The inner three planets in the system were also found to be more enriched in heavy elements like carbon and oxygen compared to their host star, further evidence they formed as planets rather than through gravitational instability.

  • The research results were published in the journal Nature Astronomy in 2026.

The players

Jean-Baptiste Ruffio

A research scientist at UC San Diego and former postdoctoral scholar at Caltech, who led the analysis of the JWST data.

Jerry Xuan

A 51 Pegasi b Fellow at UCLA and former postdoc at Caltech, who created detailed atmospheric models to compare to the JWST spectra.

Charles (Chas) Beichman

A co-author of the study and a senior faculty associate at IPAC, a science and data center for astronomy at Caltech.

Dimitri Mawet

The David Morrisroe Professor of Astronomy at Caltech and senior research scientist at JPL, and a co-author on the paper.

Heather Knutson

Professor of planetary science at Caltech, and a co-author on the paper.

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What they’re saying

“With its unprecedented sensitivity, JWST is enabling the most detailed study of the atmospheres of these planets, giving us clues to their formation pathways.”

— Jean-Baptiste Ruffio, research scientist (Nature Astronomy)

“The quality of the JWST data is truly revolutionary, and existing atmospheric model grids were simply not adequate. To fully capture what the data were telling us, I iteratively refined the chemistry and physics in the models.”

— Jerry Xuan, 51 Pegasi b Fellow (Nature Astronomy)

“Astronomy is driven by observations, and then the theorists have to explain it. The theorists come up with new ideas that go back to the experimentalists, and the process starts all over. This is how we expand our knowledge, and it is happening every day with JWST and telescopes around the world.”

— Charles (Chas) Beichman, senior faculty associate (Nature Astronomy)

What’s next

The researchers plan to continue studying the HR 8799 system and other distant exoplanets with JWST to further understand how super Jupiters and other massive planets form.

The takeaway

The detection of sulfur in the atmosphere of a super Jupiter-sized planet around another star suggests these massive, distant planets can still form through the same core accretion process that formed Jupiter in our own solar system, expanding the known limits of this planetary formation mechanism.