Planets take shape inside disks of gas and dust surrounding young stars, but the supply of gas they depend on is temporary. New observations from NASA's James Webb Space Telescope (JWST) are giving astronomers a clearer picture of how that gas escapes and how the dominant escape mechanisms change as planetary systems mature. The study, led by Naman Bajaj of the University of Arizona and coauthored by SETI Institute scientist Uma Gorti, examined 72 young, Sun-like stars and their protoplanetary disks.
It is among the largest studies of planet formation conducted with JWST and suggests that different kinds of winds dominate at different stages of a system's early development. The findings have been published in The Astronomical Journal. "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. Our solar system is now about 4.5 billion years old and consists mostly of empty space. During its first few million years, however, the young Sun was surrounded by a dense protoplanetary disk containing roughly 100 times more gas than dust.
Nearly all of that gas eventually disappeared. Understanding when and how this material is lost matters because gas is essential for forming giant planets such as Jupiter and Saturn. If a disk loses its gas too quickly, developing planets may not have enough time to accumulate the enormous atmospheres needed to become gas giants.
Bajaj and his colleagues investigated this process using archival observations from JWST's Mid-Infrared Instrument (MIRI). The 72 systems span different stages of planetary development. Taken together, they provide something like a sequence of snapshots, allowing researchers to reconstruct how gas dispersal changes as systems grow older.
In 2020, LPL professor Ilaria Pascucci, second author of the paper and Bajaj's advisor, led a related study examining how jets and winds evolve. Before JWST, researchers could not directly observe molecular hydrogen, but the team predicted that molecular winds should exist and could be dense enough during the earliest stages to block X-ray photons. By directly tracing molecular hydrogen in the new observations, Bajaj's team confirmed those predictions with JWST images.
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