Planet-sized crashes are shaking up young star systems, Webb data suggest

Twenty-one young stars wrapped in unusually bright, dusty disks have given astronomers their largest sample yet of what looks like the aftermath of worlds colliding. About a third of the disks carry a chemical signature consistent with Mars-sized bodies smashing together at high speed, and the rest point to gentler impacts, including grazing hits between Moon-sized objects.

Kate Su of the Space Science Institute in Boulder, Colorado, led the study, which relies on the James Webb Space Telescope and on archival data from its predecessor in the infrared, Spitzer. It was published in The Astrophysical Journal, volume 1010, issue 1, on 1 October 2026 (DOI 10.3847/1538-4357/ae88fe), and NASA announced it the same day with a Webb feature on planet-shattering collisions.

A 21-disk sample from Webb and Spitzer

The disks belong to a rare class called extreme debris disks. They hold smaller dust grains than a typical debris disk, an unusually large amount of warm dust close to the star, and brightness that changes irregularly over time. According to NASA’s account of the work, scientists estimate roughly 1 percent of young stars show this phase, even though models predict it should be more common.

Five of the 21 disks come from archival observations by NASA’s Spitzer Space Telescope, which retired on 30 January 2020. The other 16 were studied with Webb: 12 newly observed systems and follow-up observations of four disks Spitzer had examined. Both observatories characterized the dust through mid-infrared spectra, which reveal what the grains are made of. Su said it is the first time enough systems have been gathered to truly understand the subclass, and that before Webb the available information was limited.

The category has a precise astronomical definition. As the Wikipedia entry on debris disks describes it, an extreme debris disk radiates more than 1 percent of its star’s luminosity in the infrared, from warm dust at roughly 200 to 600 kelvin located within a few astronomical units of the star, the zone where terrestrial planets form. Spitzer spectra showed that this dust is mostly small silicate particles, and about 24 such disks were known as of 2024. Dust that fine is blown away or dragged into the star within about 10 million years, so a disk that stays bright must be fed by fresh collisions between large bodies.

Silica-rich disks and the Mars-sized collisions behind them

Composition splits the sample. About one-third of the disks are silica-rich, and the authors link them to high-energy impacts between Mars-sized bodies that vaporize much of the material. The remaining two-thirds are silica-poor, which the authors tie to lower-energy events such as grazing collisions between Moon-sized objects.

The planetary embryos in question are far too small to see directly. Ágnes Kóspál of Konkoly Observatory in Budapest said astronomers have no other way to study these planetary embryos directly, which makes the dust they throw off the only available evidence. A debris disk is normally fed by collisions between leftover planetesimals, but extreme debris disks are thought to come from one or more giant collisions rather than the smaller, ongoing grinding behind most.

Stars younger than 300 million years and the Moon’s origin

Age sorts the two groups too. Silica-rich disks turn up only around stars younger than 300 million years, while silica-poor disks occur across a wider age range and tend to vary more in brightness. Only three disks in the sample fit the older age criteria. Attila Moór of Konkoly Observatory said no silica-rich systems are expected among older extreme debris disks, a prediction that further Webb observations of older systems can test directly.

The timing echoes the solar system’s own history. NASA notes that Earth and the Moon formed about 100 million years after the Sun, and NASA’s account of lunar origins holds that the Moon was born when a large object, perhaps a single body about the size of Mars and named Theia, struck the young Earth roughly 4.5 billion years ago and threw molten and vaporized debris into orbit. Su and colleagues also report that the silica-rich systems line up with the period when terrestrial planets form, which is why the Earth-Moon episode is the natural comparison. The older silica-poor disks may also fit the Late Heavy Bombardment hypothesis, in which giant planet migration triggered catastrophic collisions.

The paper itself, summarized on ScienceDaily, lists co-authors Attila Moór, Ágnes Kóspál, George H. Rieke, Antranik A. Sefilian, Renu Malhotra, Ilaria Pascucci, Alan P. Jackson, Péter Ábrahám and Nicholas P. Ballering. Its sample of 21 disks is still small beside the roughly 1 percent of young stars estimated to pass through the phase, so the age-dependent split between silica-rich and silica-poor systems rests on a handful of stars, and only three of them are old enough to test the 300-million-year boundary.

This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.

More from Morning Overview