The James Webb Space Telescope just gave us our best look yet at how planets are born — by watching them smash into each other. A team led by Kate Su of the Space Science Institute in Boulder, Colorado, used Webb to map 21 “extreme debris disks”: the dusty wreckage left behind when young planets collide. The findings, published October 1 in The Astrophysical Journal, read like a forensic report on the most violent construction project in the universe.

And the most exciting part? Our own solar system probably went through exactly this phase. Including the collision that made the Moon.

Reading the wreckage

Extreme debris disks are rare — only about 1% of young stars show them, rarer than theory predicted. But they’re precious, because they’re the only direct evidence of the giant-impact phase of planet formation: the era when planetary embryos, Moon-sized and Mars-sized, crashed into each other and merged into the planets we know.

Webb’s mid-infrared spectra let the team do chemistry on the wreckage. One-third of the sample is silica-rich — the signature of high-energy impacts between Mars-sized bodies, found only around stars younger than 300 million years. The other two-thirds are silica-poor, pointing to gentler grazing collisions between Moon-sized objects. Co-author Agnes Kospal of Konkoly Observatory put it well: there’s “no other way to study these planetary embryos directly because they are too small.” The dust is the fossil record.

The Moon connection

Here’s where it gets personal. The silica-rich collisions mirror the Theia impact — the Mars-sized body that slammed into the early Earth and created the Moon. We’re watching, around other stars, the same kind of event that gave us our night sky. The silica-poor older disks may even connect to the Late Heavy Bombardment, the ancient era of impacts that scarred the Moon’s face.

Three shared properties confirmed across the sample: smaller dust grains than normal disks, a high concentration of warm dust, and irregular brightness variations — the flickering signature of fresh collisions still settling. These aren’t quiet, finished systems. They’re active construction sites.

Why this is a first

Sixteen of the disks were observed by Webb (12 of them new), with five more from Spitzer archival data — the first sample large enough to actually understand this phase of planet formation rather than just glimpse it. Before Webb, astronomers could see that something dusty was there. Now they can tell you what smashed into what, and how big the pieces were.

Every time Webb turns its eye to a new corner of planet formation, the story gets richer — from stellar nurseries hiding newborn brown dwarfs to, now, the collision zones where worlds are assembled. The universe builds planets the messy way: by breaking things. And for the first time, we can read the breakage like a book.