For the first time, NASA’s Hubble and James Webb space telescopes were used together to study trans-Neptunian objects , the small, icy bodies that orbit the Sun beyond Neptune. of the work describes 27 newly discovered objects. The tiniest one measures approximately 3 miles (5 kilometers), which is about five times smaller than the faintest object that can be detected by the most sensitive telescope on Earth.




This study was done by two teams of doctoral candidates from the University of Victoria and Northern Arizona University. According to NASA, the findings were published on 8 September 2026. “The Luminosity Function of Ultra-Faint Trans-Neptunian Objects Detected by JWST,” led by Marielle Eduardo, appeared in The Astronomical Journal. Its companion, “Combined JWST and HST Deep Imaging to Characterize the Smallest Known Trans-Neptunian Objects,” led by Anastasia Morgan, was also published in The Astronomical Journal.



Webb scanned 0.05 square degrees of sky across three epochs




According to The they imaged the 20-tile mosaic with Webb’s NIRCam instrument three times, about five days apart, between 24 January and 4 February 2023. Using a shift-and-stack method along with a machine learning network, moving objects have been detected from these images. According to the researchers, the result obtained is the deepest solar system search till date. Ground-based searches can detect objects down to about 50 km, while the deepest Hubble search to date detected objects down to about 30 km.



Hubble recovered 13 of the objects and measured their colours




Webb made the discoveries and Hubble made the optical observations. The Morgan group used 99 Hubble orbits at nine different points covering 65% of Webb’s field of view. They recovered 13 of Webb’s discoveries in their Hubble images and combining Hubble’s optical data with Webb’s infrared data gave colours spanning 0.35 to 3.2 µm.



Small objects kept the same colours as larger ones




It was anticipated that the surfaces of smaller bodies would be affected by collisions, so their colours must have been different from those of bigger counterparts. However, the cold classical bodies within near-circular orbits had a limited colour range, corresponding to the same colour series exhibited by bigger bodies. The authors did not find evidence of a difference in colour at smaller sizes.






Fewer small objects turned up than some models predicted




Eduardo’s team found that the magnitude distribution of the detected bodies follows a single power law, with a slope of 0.29. The dynamically “hot” and “cold” subgroups follow the same power law, even though they are thought to have formed at different distances from the Sun. The authors say this suggests that planetesimal formation produced similar size distributions under different conditions in the disk. According to NASA, there were fewer tiny bodies than predicted by some models of planet formation.



Hot and cold objects began in different places




According to NASA, the cold objects are still in their original orbits within the plane of the solar system. The hot objects formed between the current locations of Uranus and Neptune, but were displaced further out due to migration of giant planets. The orbits of these objects are very eccentric and they are still in and out of the plane of the solar system. Both categories retained their original colour scheme like that of larger bodies, implying little has happened on their surfaces since the formation of the solar system.