JWST Study Reveals How Gas Escapes Planet-Forming Disks
New observations from NASA's James Webb Space Telescope (JWST) have provided the most detailed look yet at how gas escapes from planet-forming disks around young stars. The research, led by Naman Bajaj from the University of Arizona and co-authored by SETI Institute scientist Uma Gorti, studied 72 young, sun-like stars and their protoplanetary disks. It is one of the largest planet-formation studies using JWST.
The findings, published in The Astronomical Journal under the title "JWST/MIRI Reveals the Evolution from Molecular to Atomic Disk Winds," show that different types of winds dominate at different stages in a planetary system's early life.
A Race Against Time
"What is exciting about this study is that we can now see, across a large sample of young systems, how the mechanisms that remove gas from planet-forming disks change with time. Disk dispersal sets a fundamental clock for planet formation: once the gas is gone, the opportunity to build gas-rich planets is essentially over," said Gorti.
Today, our solar system is about 4.5 billion years old and mostly empty space. In its first few million years, though, the sun was surrounded by a thick protoplanetary disk containing about 100 times more gas than dust. Most of that gas eventually vanished. Understanding how and when this happens is crucial because the gas in these disks is the main ingredient for giant planets like Jupiter and Saturn. If the gas dissipates too quickly, these planets might not have enough time to build up their thick atmospheres.
Tracking Winds with JWST
Using archival data from JWST's Mid-Infrared Instrument (MIRI), the team tracked matter loss by following the movements of molecular hydrogen, one of the most common molecules in protoplanetary disks. Each of the 72 stars represented a different stage in the early life of a star system, allowing the researchers to construct a "movie" of a planetary system's evolution.
The observations revealed a clear progression. Early on, powerful, magnetically driven jets and winds dominate the mass loss. But later, as the disk thins and starlight can penetrate more easily, these magnetically driven winds weaken. At that point, photoevaporation—the process by which high-energy radiation from the star ionizes gas and blows it into space—takes over as the dominant mechanism.
This shift in dominance is significant because gas giants like Jupiter and Saturn require vast amounts of material to form their massive atmospheres. The team's next goal is to determine exactly how much gas these winds remove over time and where in the disk the escaping material originates.
The research was supported by archival data from JWST, which continues to provide unprecedented views of the early stages of planet formation.