Young stars, similar to our Sun, are not born in a void. Around them swirl dense disks of gas and dust—true cosmic cradles where planets are born. But the gas, the main building material for the atmospheres of giants like Jupiter and Saturn, is not eternal. It gradually slips away, and the window of opportunity closes rapidly.
New observations from the James Webb Space Telescope, covering 72 young stellar systems, have for the first time allowed us to see exactly how this happens at different stages of protoplanetary disk evolution. The study, whose results were published in The Astronomical Journal, was led by Naman Bajaj from the University of Arizona. Among the co-authors is SETI Institute scientist Uma Gorti, who has studied the dispersal processes of such disks for decades.
Data from Webb's MIRI instrument became a kind of film reel: each system is a frame in a movie about the first millions of years of planetary evolution. In the youngest disks, where matter is still actively falling onto the star, powerful jets and broad winds dominate. They are driven by magnetic fields permeating the disk. Molecular hydrogen—the most common molecule in these regions—and ionized neon help scientists track the flows that carry away mass and angular momentum.
Over time, the picture changes. When the flow of matter onto the star weakens, jets quiet down, and winds become predominantly atomic. High-energy radiation from the star itself—ultraviolet and X-rays—breaks through the thinning gas, heats it, and causes it to fly away. This process, known as photoevaporation, gains increasing importance. It is precisely this that Gorti has long studied, and now observations confirm how theory aligns with reality across dozens of systems.
"Planet formation is a race against time," noted Bajaj. "Gas giants like Jupiter must gather their massive atmospheres while the disk is still dense enough to supply them, before winds and jets carry this raw material away into space."
Gorti adds: disk dispersal sets the fundamental clock. Once the gas disappears, the opportunity to build gas-rich planets practically ends. In 66 of the 72 disks, scientists observed extended outflows of molecular hydrogen and ionized neon. Conical molecular winds were detected in 46 systems, fast neon jets in 40. Each system with a neon jet also showed signs of a wind in hydrogen or oxygen.
These data continue earlier work by the same group. In 2024, using Webb, they managed to photograph how gas escapes from the disk around the young star T Cha. Now the scale has grown to dozens of objects, and it becomes clear: no single mechanism acts alone. Systems transition from a stage of strong magnetic jets to an era of atomic winds, including photoevaporation.
Ahead lie precise measurements of how much gas is carried away and from which zones of the disk. This will help understand not only how quickly the window for giants closes, but also where exactly different types of planets manage to form. For now, the observations remind us: in the Universe, everything is connected in astonishing ways. Giant outflows, magnetic fields, radiation from young stars, and subtle chemical traces work together, creating conditions in which worlds like ours sometimes manage to be born. We live in a cosmos where even the birth of planets is a dramatic race over millions of years, and the Webb telescope for the first time allows us to see it in all its grand fullness.
