Planets form in rotating disks of gas and dust that surround young stars. These protoplanetary disks supply the raw material from which solid cores and later gaseous envelopes can grow.
However, young stars are far from tranquil. They launch powerful stellar winds and high‑energy radiation that can strip away or even destroy the gas in the disk.
Consequently, planet formation is a race against time. Gas giants, which need to accrete large amounts of hydrogen and helium, have only a few million years before the gas reservoir is depleted.
Observations with radio telescopes reveal that many disks show significant gas loss after just one to two million years. This limited timespan explains why some planetary systems end up with only rocky worlds, while others also produce massive gas planets.