Hubble and JWST's first joint survey finds 27 pristine small Trans-Neptunian Objects
Hubble and James Webb teamed up for the first time to discover 27 small Trans-Neptunian Objects, revealing fewer tiny icy bodies than models predicted and surfaces as pristine as those of larger worlds.
For the first time, scientists used the joint power of NASA’s Hubble and James Webb Space Telescopes to study some of the most far-flung bodies in the solar system, Trans-Neptunian objects (TNOs) orbiting beyond Neptune. The two observatories collectively discovered 27 new TNOs, all less than 25 miles (40 km) across, with the smallest only 6 miles (10 km) in diameter, and researchers unexpectedly found fewer small TNOs than expected while the colors followed the same relationships as larger TNOs — meaning the small bodies remained pristine since formation.
The deficit of small bodies is the surprise. The campaign turned up fewer tiny TNOs than models had predicted, even though every one of the 27 new objects sits below the 25-mile (40 km) size cutoff and the smallest measures just 6 miles (10 km). A population count that thins out at the small end runs against the standard expectation that collisions would grind larger bodies into many smaller fragments.
Color data supplies the second result. The new TNOs displayed the same color relationships seen in larger known bodies, which indicates these small worlds have not been churned by impacts since they formed. Their surfaces still record primordial conditions rather than a mixed mantle laid down by later collisions.
Independent reporting confirmed the Hubble–Webb discovery of 27 new Trans-Neptunian Objects beyond Neptune and noted the findings were led by PhD candidates Anastasia Morgan (NAU) and Marielle Eduardo (U Victoria), with the small bodies appearing as pristine as when they formed, contradicting models predicting impact-mixed surfaces. The account, published after NASA’s September 8 summary, reinforces that the pristine-state signal is not an artifact of one telescope’s processing.
What makes the contradiction interesting is that impact mixing was the expected norm for small bodies. A 6-mile (10 km) object has weak gravity and a high surface-to-volume ratio, so models predicted its icy surface would be shuffled by even minor collisions, blurring any original color grouping. The observed continuity with larger TNOs therefore suggests the outer solar system’s collision environment was calmer than assumed, or that these bodies formed already coherent enough to resist churning.
The joint observing run also marks a practical milestone: two flagship telescopes, paired for the first time on this class of target, extended detection into the sub-25-mile (40 km) regime at extreme distance. Twenty-seven new objects is a small catalog, but as a first cross-calibration of Hubble and JWST on the solar system’s outer fringe, it establishes a baseline for future surveys that may finally resolve whether the missing small TNOs were never there in modeled numbers or simply await a deeper search.