MIRI observations of 72 disks around young stars show how the mechanisms of gas loss change as the system matures: initially jets and winds associated with magnetic fields dominate, and later atomic and photoid winds become increasingly important. For Jupiter-like gas giants, the implication is clear—they must accumulate their thick atmospheres before the raw material is dispersed into space.
The James Webb Space Telescope reveals how young planetary systems gradually lose the gas from which planets are supposed to be built. New study of 72 Preplanetary disks indicates a transition between two regimes of material loss: in the early stages, Jets and winds that also contain molecular gas and are compatible with mechanisms controlled by magnetic fields; later the jets weaken and the winds become more atomic, a situation consistent with an increasing role of photoemission by the star's high-energy radiation.
In terms of Giant planets, it's a race against time. Jupiter and Saturn couldn't have been built from just dust and rocks. After forming a massive core, they had to accumulate large amounts of hydrogen and helium from the disk. Once the gas dissipates, the possibility of building a giant envelope is almost closed.
The study, led by Naman S. Bajaj of the University of Arizona, was published on August 25, 2026 in The Astronomical Journal. The researchers used archival data from an instrument MIRI On the web, we examined 72 disks, most of them around young Class II stars.
72 systems instead of waiting millions of years
It is impossible to follow a single disk over millions of years and see how it changes from the beginning of star formation to the disappearance of the gas. So astronomers use a different method: comparing many systems at different stages of development and constructing an approximate sequence from them.
In the current study, the accretion rate—the rate at which material from the disk continues to fall onto the young star—was used as one measure of the developmental state. Systems with a high accretion rate generally represent a younger, more active phase; when the accretion rate decreases, the disk is already well advanced in its depletion process.
Webb gave researchers an important advantage because MIRI is sensitive to the mid-infrared and can track emission lines from molecular hydrogen, H2, and ionized neon, [Ne II]. These two markers allow us to distinguish between different types of flows emerging from the disk.
Hydrogen and neon tell different stories
Extended emission of molecular hydrogen and/or ionized neon was found in 66 of the 72 systems. The researchers identified conical structures consistent with molecular hydrogen winds in 46 systems, and in 40 systems, fast [Ne II] jets perpendicular to the disk plane were found.
Molecular hydrogen follows some of the cooler, denser gas in the broad winds emanating from the disk. Ionized neon can appear in two different states: in more active systems it marks fast jets, while in systems with a lower absorption rate it also appears in slower, broader winds.
Every system in which a neon jet was found also showed evidence of a wind, observed in molecular hydrogen or oxygen. This connection reinforces the picture that the jets and winds are not isolated phenomena, but part of a shared system that extracts mass and angular momentum from the disk.
At the beginning: Magnetic fields remove matter
In the younger stages, when much material is still flowing from the disk into the star, neon jets and molecular winds are more common. The pattern is consistent with magnetohydrodynamic (MHD) winds, where magnetic field lines penetrating the disk can accelerate gas outward.
These winds are not just a way to lose material. They may also remove angular momentum from the disk, allowing other material to move in and attach to the star. In a very young system, then, inflow and outflow are two sides of the same evolution.
Previous theoretical studies have also predicted that dense molecular winds in the early stages could block some of the star's X-ray radiation and shield other layers in the disk. Before Webb, it was difficult to directly observe molecular hydrogen in such winds. The new sample provides observational support for this picture.
Then the jets weaken and the radiation penetrates
As the adsorption rate decreases, the researchers found a decrease in the frequency of jets and hot molecular winds. At the same time, slow atomic winds observed using [Ne II] become more important.
The interpretation is that as the system thins out, there is less dense gas to block the star's high-energy radiation. Ultraviolet and X-ray radiation can penetrate deeper layers of the disk, heating the gas and giving some of it enough energy to escape the star's gravity. This process is called photoemission.
The study does not claim that every atomic wind is necessarily a pure photoid wind, or that there is a sharp moment when one mechanism turns off and the other turns on. The resulting picture is of a gradual shift in the balance: magnetic mechanisms are stronger at the beginning, and atomic winds—including those suitable for photoids—become more significant at later stages.
Jupiter's clock starts ticking early.
A gas giant must reach a stage where a sufficiently solid core can rapidly pull in surrounding gas. If this stage comes too late, the disk may already be too thin to provide the hundreds of Earth masses of gas needed to build a Jupiter-like world.
Therefore, the lifetime of a disk is not just a detail in the formation process of a system; it determines what types of planets can form in it. Two disks that start with similar masses can give rise to different systems if one loses gas faster than the other.
The researchers emphasize that the next step will be to better measure how much mass the winds carry and identify from what distances from the star the material is being released. Only then will it be possible to directly link the rate of disk dispersion to the regions where different types of planets can still form.
From T Cha to a sample of dozens of systems
The new study follows on from previous work by the same team. In 2024, the researchers used Webb to observe a disk wind around the young star T Cha. In that study, [Ne II] emission from a disk wind was first detected when it was spatially separated from the disk itself.
This time, the study was expanded from a single system to a sample of dozens of systems. The advantage is not just statistical: when disks with different adsorption rates are placed side by side, a sequence is revealed in which the jets and molecular winds are prominent at first, while the atomic component gradually takes on a more central role.
This is also an important use of archival data. The researchers didn't need a new observing program to image 72 stars from scratch; they combined MIRI observations collected under different programs and analyzed them in a unified way to answer a broader question about the evolution of planetary systems.
Not a clock with a fixed end date
The phrase "race against time" does not mean that every disk disperses after exactly a fixed number of millions of years. The rate of evolution depends on the mass of the star, the mass of the disk, the magnetic field, the radiation, and the environment in which the system was born.
The sample itself is not a direct movie of a single system either. It is made up of different systems representing different stages, so the evolutionary sequence is a statistical reconstruction. However, the fact that the relationships between adsorption rate and flow types appear in a large sample provides stronger support than what can be obtained from a small number of individual systems.
For research The formation of planetsThe simple message is that the material in the disk doesn't wait. As dust grains stick together, planetary cores grow andGas giants Trying to accumulate atmospheres, other mechanisms are already working to remove the exact same material. The planetary system is being built and at the same time breaking down its building materials.
Questions and Answers
What did the James Webb Space Telescope examine?
The researchers analyzed MIRI observations of 72 protoplanetary disks around young stars and looked for spatial emission of molecular hydrogen and ionized neon, which serve as markers for winds and jets emerging from the disks.
What is in the 72 systems?
Extended emission of molecular hydrogen and/or ionized neon was found in 66. Conical molecular winds were detected in 46 systems, and fast neon jets in 40.
Why are giant planets in a race against time?
Gas giants need to accumulate large amounts of hydrogen and helium from the disk. If jets and winds disperse the gas before the planetary core grows large enough, there is no material left to build a giant atmosphere.
What changes as the disc ages?
In the more active phases, jets and winds consisting of molecular gas are prominent and are consistent with magnetic mechanisms. As the rate of adsorption decreases, the jets and molecular component weaken and the winds become more atomic; then the role of photodiode driven by the star's radiation may increase.
The scientific article
JWST/MIRI Reveals the Evolution from Molecular to Atomic Disk Winds — Naman S. Bajaj et al., The Astronomical Journal, published online August 25, 2026.
More on the subject on the science website
- The James Webb Space Telescope reveals the unseen forces that shape planetary systems
- A solar system in the making? Two planets observed forming in a disk around a young star
- What is the maximum size of a planet? After discovering huge gas giants, it's hard to know
- The James Webb Space Telescope challenges theories about the formation of planets in the early universe
- The Webb Space Telescope finds an abundance of carbon molecules around a young star
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