Webb telescope shows planet formation is a race against time

New observations from the James Webb Space Telescope suggest that giant planets have only a limited time to form before the raw material they need is blown away.

A team led by Naman Bajaj of the University of Arizona studied 72 young stars similar to the Sun, each surrounded by a protoplanetary disc, the swirling cloud of gas and dust from which planets are born. The research, which involved scientists from the SETI Institute, was published in The Astronomical Journal.

How discs disappear

The astronomers found that discs lose their gas through different processes at different stages of their lives. In the youngest systems, powerful jets and molecular winds driven by magnetic fields carry material away. As systems mature, they shift towards atomic winds and photoevaporation, in which radiation from the star heats the gas until it escapes.

Webb detected extended emission in 66 of the 72 discs. Conical winds of molecular hydrogen were seen in 46 systems, and fast-moving jets traced by neon in 40.

A deadline for giant planets

"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 co-author Uma Gorti of the SETI Institute.

That means gas giants such as Jupiter and Saturn must gather their thick atmospheres before winds clear the disc, setting a strict deadline for how giant planets form.

Why Webb makes the difference

The telescope's sensitivity to infrared light lets it see the faint glow of gas in and above these discs in far greater detail than earlier instruments. By comparing many systems of different ages, the team could piece together the sequence of events rather than relying on a single snapshot.

The findings help explain why planetary systems vary so much, and why our own solar system, with its mix of gas giants and rocky planets, turned out the way it did. Ilaria Pascucci was among the other authors of the study.