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JWST Detects a Planet-Forming Disk in a UV-Extreme Stellar Nursery
Using the James Webb Space Telescope (JWST) and advanced thermochemical modeling, a team led by astronomers at Penn State has shown that the raw materials for rocky planets can persist even inside protoplanetary disks exposed to intense ultraviolet (UV) radiation. The target, a young Sun-like star labeled XUE 1 in the Lobster Nebula (NGC 6357), sits roughly 5,500 light-years from Earth within a region dominated by more than 20 massive, UV-luminous stars. Despite this harsh radiation, JWST spectra and models indicate a compact disk around XUE 1 that still contains the dust and gas necessary to build planets.
The new results, published in The Astrophysical Journal, combine high-sensitivity JWST mid-infrared observations with state-of-the-art astrochemical and thermochemical models. This dual approach allowed the team to infer both the solid mass in the disk and the distribution of key volatiles — molecules such as water vapor (H2O), carbon monoxide (CO), carbon dioxide (CO2), hydrogen cyanide (HCN) and acetylene (C2H2) — which play central roles in planetary atmospheres and volatile delivery to rocky worlds.
Scientific Background: Why UV Radiation Matters for Planet Formation
Ultraviolet radiation carries more energy than visible light and can break apart molecules and heat gas. On Earth, our atmosphere shields life from harmful UV. In star-forming regions, massive O- and B-type stars emit prodigious UV flux that can photoevaporate surrounding gas, erode dust, and chemically alter protoplanetary disks. Most detailed studies of disks have focused on relatively calm, nearby star-forming regions that lack this extreme UV environment. Disks in massive stellar nurseries, however, are more representative of where most stars — and therefore most planets — likely form.
By targeting XUE 1 in the Lobster Nebula, a region that includes some of the Milky Way’s most massive and UV-bright stars, the researchers tested whether planet-forming solids and volatiles can survive under sustained, external irradiation. Thermochemical modeling is crucial here: it translates observed spectral signatures into estimates of temperature, chemical abundances, and the mass and size distribution of dust grains that will become planetesimals and, ultimately, planets.
Key Findings: Compact, Gas-Depleted Disk but Enough Solids to Seed Planets
The JWST observations reveal signatures of dust grains and gas-phase molecules in XUE 1’s disk. Model fits indicate the disk is compact — extending to roughly 10 astronomical units (AU), about the distance from the Sun to Saturn — and shows a deficit of gas in its outer regions. The team interprets this compactness as the result of external photoevaporation driven by intense nearby UV sources: the outer disk has been stripped away, leaving a smaller, denser inner disk.
Crucially, the inner disk still contains sufficient solid material to form multiple terrestrial-mass planets. The study estimates enough solids to produce at least ten bodies with masses comparable to Mercury. The presence of water vapor and carbon-bearing molecules in measurable amounts also suggests that volatile reservoirs capable of contributing to nascent planetary atmospheres have endured the UV assault.
Konstantin Getman, co-author and research professor at Penn State, notes that the detection of both dust and molecules supports the idea that "the building blocks for planet formation can exist even in environments with extreme ultraviolet radiation." Similarly, lead author Bayron Portilla-Revelo emphasizes that studying disks in UV-intense nurseries addresses a major gap in our understanding of planet formation in realistic galactic conditions.

Evidence of Disk Erosion and the Role of Photoevaporation
The lack of certain UV-sensitive molecular tracers in the JWST spectra helped the team infer the gas-depleted nature of the disk’s outskirts. Photoevaporation by external UV light preferentially removes the less gravitationally bound gas and small dust at large radii, shrinking disk size and potentially altering the timeline and pathways of planet formation. Despite this erosion, inner regions can remain dense and shielded enough for solids to grow and stick together, enabling the formation of rocky planets.
Eric Feigelson, distinguished senior scholar at Penn State and a co-author, underscores the broader implication: "These findings support the idea that planets form around stars even when the natal disk is exposed to strong external radiation," a perspective that helps explain why planetary systems appear common across the Galaxy despite environmental diversity.
Expert Insight
Dr. Amina Rahman, an astrophysicist specializing in disk evolution (independent commentator): "This study is an important proof of concept. It shows JWST’s sensitivity to molecular and dust signatures in challenging environments, and it demonstrates that photoevaporation doesn't always sterilize a disk. Instead, it sculpts disks — often stripping the outskirts but leaving inner zones where planet assembly can proceed. That has major consequences for the architecture and composition of planets formed in dense stellar clusters."
Mission and Modeling: How JWST and Thermochemical Tools Complement Each Other
JWST provides the high-resolution infrared spectra needed to detect molecular vibrational bands and solid-state features of dust. Thermochemical models then simulate the physical and chemical structure of irradiated disks, accounting for heating, cooling, photodissociation, and gas–grain reactions. By iterating between observations and models, the team constrained the disk’s temperature profile, molecular abundances, and dust mass — parameters that are otherwise difficult to measure in distant, UV-irradiated systems.
This combined methodology also refines predictions for where in the disk different molecules should appear, which informs follow-up campaigns with JWST, ALMA, and large optical/near-infrared ground-based facilities such as the Gemini Observatory.
Future Prospects: Toward a Census of Planet Formation in Diverse Environments
The XUE 1 study represents a first step toward a broader survey of disks in massive stellar nurseries. Expanding samples will clarify how common compact, UV-processed disks are and how their planet-forming outcomes differ from those in more quiescent regions. Such work will improve estimates of exoplanet demographics, especially the frequency and composition of rocky planets formed in clusters where most stars originate.
The research also highlights JWST's transformative capability to probe disk chemistry at distances and in conditions previously inaccessible. Combined with ground-based radio interferometers and next-generation telescopes, these observations will build a more complete picture of planet formation across the Milky Way.
Conclusion
JWST observations of the protoplanetary disk around XUE 1 in the Lobster Nebula demonstrate that, even in regions bathed in extreme ultraviolet radiation, a compact reservoir of dust and volatile molecules can survive long enough to seed the formation of rocky planets. External UV radiation appears to erode outer disk regions, producing compact, gas-depleted structures, but it does not necessarily prevent planet formation. These results expand our view of planet-forming environments and underscore the importance of combining high-sensitivity infrared observations with advanced thermochemical modeling to understand planet formation in the diverse environments where stars and planets are born.

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