A young star during star formation is surrounded by a rotating cloud of cosmic dust and gas — an accretion disk (raw material for future planets). Often, jets of gas shoot out from it, like a fountain. This fountain carries away excess rotation, allowing material to fall onto the star. The longer the jets fire, the more the disk is altered, and so are the future planets.

Using the MIRI instrument aboard the JWST, astronomers studied 72 such disks. They applied spectroscopy — a technique that splits light into colors to reveal gas motion. The Doppler effect (the shift in wave color due to source motion) exposed speeds: in young systems, jets raced faster than 30 km/s. But as the star’s fueling waned, the dense jets vanished. Only a faint atomic wind remained — a gentle evaporation.

The transition is explained by how the star’s radiation interacts with the disk. While the disk is dense, it shrouds the star, and the jets are sustained by magnetic forces (processes described long ago by James Clerk Maxwell). Then, as the gas disperses, harsh ultraviolet and X-rays break through and “blow away” the leftovers: this is photoevaporation. The cosmic fountain quiets, leaving behind a cleared system where exoplanets (planets of other stars) will later emerge. The winds also slow planetary migration (orbital shifts), preventing planets from plunging into the star. Our Earth likely endured such a turbulent youth, surrounded by a fading fountain.