Some of the most violent events in the universe leave behind the quietest evidence: dust. Around a small number of young stars, astronomers have found discs of dust far brighter and more chaotic than ordinary planet-forming material. These are extreme debris disks, and new observations from the James Webb Space Telescope have turned them into a forensic record of worlds colliding, grinding each other to vapour and rebuilding themselves from the wreckage.

Extreme debris disks are rare, appearing around only about one percent of young stars in surveys so far, which suggests the smash-up phase they record is brief in a star system's life. They differ from the gas-rich disks where planets are born, because the gas is mostly gone and the dust is freshly made, not primordial. The dust grains are also unusually small and their brightness changes irregularly, both signs of recent, energetic collisions rather than slow, steady grinding.

A team led by Kate Su combined Webb's mid-infrared spectra with archival data from the retired Spitzer telescope to build the largest sample of these systems yet: 21 extreme debris disks, 16 observed with Webb, 12 of them for the first time. By reading the mineral fingerprints in the dust's infrared light, the team could tell what kind of collision produced it, in much the same way a geologist reads a rock to reconstruct an ancient impact on Earth.

The key split in the sample is between silica-rich and silica-poor disks. About one-third of the disks are rich in silica, the same basic ingredient as glass, while the other two-thirds are silica-poor. The silica-rich disks are best explained by ultra-energetic collisions between Mars-sized planetary embryos, impacts violent enough to vaporise a substantial fraction of rock. The silica-poor disks point to gentler grazing encounters between bodies closer to the size of Earth's Moon.

That distinction maps directly onto the story of our own Moon. The leading explanation for the Moon's birth, the giant impact hypothesis, holds that a Mars-sized world often called Theia slammed into the young Earth billions of years ago, blasting molten and vaporised rock into orbit that later coalesced into the Moon. Webb's silica-rich disks may be distant replays of exactly that kind of event, caught in progress around other stars.

Age adds another clue. Every silica-rich disk in the sample surrounds a star younger than 300 million years, while silica-poor disks appear across a much broader range of ages. That pattern fits a picture in which the most violent embryo collisions happen early, while systems are still crowded and dynamically unsettled, and gentler collisions continue for far longer as leftover bodies keep crossing paths.

For planet formation theory, the survey matters because it tests ideas that were previously hard to observe. Models predicted that giant impacts should be common in young systems, yet extreme debris disks proved scarcer than expected, which means either the violent phase is shorter than models assumed or many collisions produce dust that fades quickly. Either way, the observations are now constraining the models rather than the other way around.

Future Webb observations will track how individual disks evolve over time, search for surviving planets inside the wreckage, and refine how much material ends up in new moons versus falling back onto the host planet. Each answer sharpens the picture of how rocky worlds, and moons like ours, are assembled. The dust around distant stars turns out to be a history book, and Webb is teaching us how to read it.

For readers who want to follow this field, the key names to watch are extreme debris disks and the FEAST and related Webb programmes, whose future papers will extend this 21-system sample and may reveal whether silica-rich disks fade quickly or persist for millions of years after their collisions.