JWST uncovers a time race in planet formation

August 25, 2026, Mountain View, California—A young planetary system may look peaceful from a distance, but new observations from NASA’s James Webb Space Telescope reveal that planet formation is taking place inside a violent race against time. Around newborn stars, vast disks of gas and dust provide the raw material for planets. Yet those same disks are gradually dismantled by powerful outflows, including magnetically driven winds, high-speed jets, and radiation-powered streams of escaping gas. By examining 72 young, Sun-like stars, astronomers have now traced how these mechanisms change as planetary systems mature, offering one of the clearest views yet of how the birthplaces of planets disappear.

The study, led by Naman Bajaj of the University of Arizona and co-authored by SETI Institute scientist Uma Gorti, uses archival observations from JWST’s Mid-Infrared Instrument, or MIRI. The instrument is particularly valuable for studying warm molecular and atomic gas surrounding young stars because it can detect faint infrared emissions hidden from many earlier observatories. Instead of following one planetary system through millions of years—a task impossible within a human lifetime—the researchers assembled observations of systems at different ages. Together, the systems act like separate frames in a cosmic time-lapse movie, allowing scientists to reconstruct how winds evolve during the first few million years of planet formation.

The results, published in The Astronomical Journal, focus on two important tracers of escaping material: molecular hydrogen and ionized neon. Molecular hydrogen is the most abundant molecule in protoplanetary disks and can reveal broad, relatively cool winds flowing away from the disk. Ionized neon, by contrast, is produced in energetic environments and can identify hotter atomic gas, including fast jets and high-velocity outflows. Because the two signals arise under different physical conditions, comparing them allows astronomers to distinguish between several processes that remove gas from a young planetary system. The team detected extended emissions from molecular hydrogen and ionized neon in 66 of the 72 disks examined.

The observations show that the earliest stages of planetary-system development are dominated by energetic outflows linked to accretion. As material spirals inward through a disk and falls onto the young star, some of the gas can be redirected outward along magnetic field lines. These magnetically driven winds remove both mass and angular momentum, helping the remaining disk continue its inward flow. In many of the youngest systems, JWST revealed broad, conical winds containing molecular and atomic gas, as well as narrow, fast-moving jets traced by ionized neon. The researchers identified molecular hydrogen winds in 46 systems and neon jets in 40, showing that these structures are not rare exceptions but common features of early planetary evolution.

Magnetic fields provide the physical link between accretion and outflow. A young star and its surrounding disk rotate rapidly, twisting magnetic field lines and creating channels through which gas can be launched into space. Some material may be expelled from the surface of the disk, while other flows can emerge closer to the star and form collimated jets. These outflows are capable of carrying away substantial angular momentum, a crucial requirement for gas to move inward and feed the growing star. At the same time, they steadily reduce the reservoir available to future planets. The findings suggest that disk winds are not merely secondary effects of star formation; they are active forces that help determine whether planets have enough time to assemble.

The balance changes as a planetary system ages. Accretion onto the central star gradually declines, the strongest jets weaken, and the molecular component of the outflow becomes less prominent. As the disk thins, high-energy ultraviolet and X-ray radiation from the young star can penetrate deeper into the remaining gas. This radiation heats the gas and gives particles enough energy to escape the star’s gravity, a process known as photoevaporation. Unlike magnetically driven winds, which rely primarily on the disk’s magnetic structure and rotation, photoevaporative winds are powered by stellar radiation. The later-stage outflows observed by JWST are increasingly atomic, consistent with a transition from dense, magnetically controlled environments to more exposed and radiation-heated disks.

That transition has immediate consequences for planet formation. Protoplanetary disks typically contain far more gas than dust; during the early history of our own solar system, the disk surrounding the newborn Sun may have held roughly 100 times as much gas as dust. Dust grains collide and stick together, eventually building planetesimals and rocky planetary cores. If a core becomes sufficiently massive while hydrogen and helium remain abundant, it can rapidly capture a thick atmosphere and develop into a gas giant such as Jupiter or Saturn. But once disk dispersal accelerates, the supply of atmospheric gas can vanish. A planet that grows too slowly may remain a rocky or ice-rich world even if it formed in a region where a gas giant could otherwise have developed.

The new observations confirm predictions from earlier theoretical and observational work. In 2020, a team led by University of Arizona Lunar and Planetary Laboratory professor Ilaria Pascucci, who is also the second author of the current study and Bajaj’s advisor, predicted that molecular winds should be present in younger disks and could be dense enough to absorb or block X-ray radiation. At the time, astronomers could not directly observe molecular hydrogen in the relevant environments. JWST has now provided the needed sensitivity, revealing the predicted molecular outflows across a large sample and linking them to the later appearance of predominantly atomic winds. The study therefore connects models of disk evolution with direct infrared evidence from dozens of planetary systems.

The scale of the survey also changes the way scientists can think about disk dispersal. In earlier studies, a spectacular outflow from a single system could be interpreted in several ways because researchers did not know whether it represented a typical stage or an unusual event. The 72-system sample offers statistical context. Every system with a detected neon jet also showed evidence of a wind traced by molecular hydrogen or oxygen, indicating that jets and broader winds are closely related rather than independent phenomena. The observations support a picture in which planetary systems pass through overlapping phases: strong molecular and atomic outflows appear early, jets fade as accretion declines, and photoevaporative winds become increasingly influential as stellar radiation reaches the exposed disk.

The researchers’ next challenge is to measure how much gas each type of wind removes and determine precisely where the escaping material originates. The answer may reveal whether disk dispersal is controlled mainly by winds launched near the star, by evaporation from the outer disk, or by a combination of mechanisms that varies from system to system. Those measurements could also help explain the remarkable diversity of planets seen around other stars. Some systems may lose their gas rapidly and produce compact rocky worlds, while others may preserve their disks long enough to build massive gas giants. JWST’s survey shows that the end of a planet-forming disk is not a single event but an evolving contest between accretion, magnetic fields, stellar radiation, and gravity. In that contest, the moment when a young world gathers its atmosphere may be determined by how quickly its star blows the building materials away.

News Publication Date: August 25, 2026

Web References: https://www.seti.org/people/uma-gorti/ ; https://doi.org/10.3847/1538-3881/ae9089

References: The Astronomical Journal, DOI: 10.3847/1538-3881/ae9089

Keywords

James Webb Space Telescope, JWST, protoplanetary disks, planet formation, molecular hydrogen winds, atomic disk winds, photoevaporation, magnetically driven jets, young stars, gas giants, planetary systems, astronomy