// NASA BREAKING NEWS — SPAZIO & SCIENZA
NASA’s Webb Provides Crash Course on Planet-Shattering Collisions
In the early history of our solar system, scientists theorize that a Mars-sized object called Theia smashed into the infant Earth, vaporizing massive amounts of rock and blasting it into space. Some of that material coalesced into the Moon, where NASA’s Artemis program is returning humans, preparing for Mars, and shaping the future of space exploration.
That long-ago, violent collision reshaped our home planet. Astronomers have used NASA’s James Webb Space Telescope to examine a class of young stellar systems that show signs of similar upheavals, providing clues to the amount of energy in their collisions. The results offer insights into the composition and evolution of these chaotic systems.
The team’s findings published Thursday in The Astrophysical Journal.
The environment surrounding a star changes as it ages, beginning with a juvenile, gas-rich protoplanetary disk where forming planets can reside, before evolving to a gas-poor debris disk. During its mission lifetime, NASA’s retired Spitzer Space Telescope examined the debris disk stage and discovered a subclass termed extreme debris disks. These systems harbor unusually large amounts of warm dust close to the star, in the region comparable to where rocky planets orbit in our solar system. A team of astronomers led by Kate Su of the Space Science Institute in Boulder, Colorado investigated these intriguing objects with Webb.
Contrary to theoretical predictions, which suggest we should observe many extreme debris disks, observations indicate that these environments are rare. Scientists estimate roughly only 1% of young stars show observable signatures of this phase based on the data collected so far, including possibly our own solar system during its formation. Despite their rarity, the team was able to compile a sample of 21 extreme debris disks, including five from Spitzer’s archival data and 16 from Webb, with 12 newly observed disks and follow-up observations on four of Spitzer’s.
“This is the first time we have gathered enough systems to truly understand this subclass that we call extreme debris disks,” said Su, lead author of the paper. “Before Webb, we had limited information. We knew that they are weird and very different from the typical cold debris disks that we know, like Vega and Fomalhaut. Now that we have more data, we can pin down what these disks represent for planet formation and evolution.”
The team confirmed that extreme debris disks share three key properties: smaller dust grains than those in protoplanetary or classic debris disks, a high concentration of warm dust, and irregular brightness variations, all revealed by mid-infrared spectra from Webb and Spitzer.
To determine the driving factor for these qualities, the team studied the mineralogical makeup of the disks. They found that their sample could be categorized into silica-rich and silica-poor disks. Volcanic glass like obsidian is one example of silica-rich material found on Earth, whereas the silica-poor mineral forsterite appears as green sand grains on some beaches in Hawaii. An extreme debris disk’s category relays information on the type of collisions producing the impact debris and may help account for its variability in infrared brightness.
“To just see their mid-infrared emission and beautiful spectral features with Webb, which allowed us to identify their compositions, was the most exciting thing for me,” said Agnes Kospal of Konkoly Observatory in Budapest, Hungary, and a coauthor of the study. “We have no other way to study these planetary embryos directly because they are too small.”
Of their sample, about one-third is silica-rich, suggesting these disks are produced by high-energy impacts between Mars-sized bodies where a significant portion of the material is vaporized. The remaining two-thirds of their sample is silica-poor, indicating that the collisions are occurring on smaller scales, like grazing, between Moon-sized objects. Silica-rich disks are found only around sta