Astronomers using NASA’s James Webb Space Telescope have found evidence of catastrophic collisions between Mars-sized worlds in young stellar systems. The study, published October 1 in The Astrophysical Journal, analyzed 21 rare extreme debris disks to see how high-energy impacts shape rocky planets.
Extreme debris disks appear around only about 1 percent of young stars, a rarity that contradicts theoretical models suggesting such environments should be common. These extreme debris disks concentrate unusually large amounts of warm dust close to their stars, mirroring the regions where rocky planets orbit in our own solar system.
Kate Su of the Space Science Institute in Boulder, Colorado, led a team using the James Webb Space Telescope (JWST)—an international program led by NASA with partners ESA (European Space Agency) and CSA (Canadian Space Agency)—to investigate these objects. The team identified three characteristic features of these disks: a high concentration of warm dust, irregular variations in brightness, and dust grains smaller than those found in typical debris or protoplanetary disks.
Dust Composition Reveals Impact Scale
Researchers analyzed the mineral composition of the dust to infer the scale of collisions because planetary embryos are too small to observe directly. Agnes Kospal of Konkoly Observatory in Budapest, Hungary, explained that the team identified disk contents by observing their light patterns and mid-infrared emissions.
- Silica-rich disks: Found in about one-third of the sample, these result from high-energy impacts between Mars-sized objects powerful enough to vaporize substantial amounts of rock. This debris is comparable to volcanic glass, such as obsidian.
- Silica-poor disks: Making up the remaining two-thirds, these stem from less energetic events, such as grazing collisions between Moon-sized bodies. These disks often contain forsterite, a silica-poor mineral seen as green sand grains on some Hawaiian beaches.
“To just see their mid-infrared emission and beautiful spectral features with the JWST, which allowed us to identify their compositions, was the most exciting thing for me,” said Agnes Kospal.
Agnes Kospal, Konkoly Observatory
Age Limits Define System Types
Every silica-rich disk was found around a star younger than 300 million years. This timeline aligns with computer simulations suggesting terrestrial planets like Earth typically form within the first few hundred million years of a system’s life.
Silica-poor disks appear across a much wider range of stellar ages and exhibit more irregular variations in infrared brightness. Scientists propose this flickering—where the dust thickens and thins, causing the disks to dim and brighten over years, months, or weeks—is caused by the rapid evolution of fresh debris as it undergoes further impacts and shifts in orbit.
Early Solar System History
Scientists theorize that a Mars-sized object called Theia slammed into the infant Earth, vaporizing rock and creating the debris that eventually coalesced into the Moon. This event likely occurred roughly 100 million years after the Sun formed, a window that fits the observed ages of silica-rich extreme debris disks.
The solar system may have also experienced a silica-poor phase during the Late Heavy Bombardment. During this period, collisions may have triggered the migration of gas giants from the inner solar system to their current positions.
“How rocky planets formed and giant planets evolved are part of the broader story of the solar system’s formation. Our work on extreme debris disks helps us bring together the big picture of what we currently understand.”
Kate Su, Space Science Institute
Sample Size Limits Conclusions
The study included 16 systems from Webb—12 of which were newly observed—and five from Spitzer archival data, four of which were re-examined. While this is the largest sample of its kind at 21 disks, uncertainties remain.
Only three disks in the sample fit the older age criteria, meaning the hypothesis that silica-rich systems vanish as stars age is based on a very small data set.
Kate Su noted that before the JWST, the team had limited information, stating, This is the first time we have gathered enough systems to truly understand this subclass that we call extreme debris disks.