Astronomers using NASA’s Hubble and James Webb Space telescopes have discovered 27 tiny, distant Trans-Neptunian Objects beyond Neptune. Published in The Astronomical Journal, the research reveals that these miniature icy bodies, some just 3 miles wide, share surprising similarities with larger members of their family, preserving clues about early planet formation.
For billions of years, the smallest inhabitants of our solar system have drifted quietly in the frozen darkness far beyond Neptune out of reach of traditional observation. These distant icy bodies, known as Trans-Neptunian Objects or TNOs, represent some of the most primitive leftover building blocks from the birth of the solar system. By pointing two of humanity’s most powerful space telescopes at the exact same patch of sky, researchers have managed to peer into this distant realm to study objects orbiting between 30 and over 100 astronomical units away from the Sun.
Joint Hubble and Webb Observations Reveal 27 New TNOs
The breakthrough came when teams coordinated simultaneous observations using different instruments. While Hubble tracked the visible signatures of the TNOs as they moved against background stars in the constellation Sagittarius, the Webb telescope captured their infrared emissions.
This dual-telescope approach allowed scientists to determine precise orbits, measure surface colors, and gauge the physical dimensions of 27 newly discovered, remarkably dim objects. Some of these newly mapped bodies measure roughly 5 kilometers—about 3 miles—in width.
Surprising Surface Properties Challenge Planet Formation Models
Before the coordinated survey, prevailing astronomical models suggested that small TNOs should look drastically different from their larger siblings. Because these objects have spent billions of years traveling through the outer solar system, scientists assumed frequent collisions would have battered the smaller bodies, stripping away their primordial outer layers and exposing fresh interior ice.
Instead, the observations delivered a surprise. The tiny TNOs displayed surface colors and compositions that closely mirrored those of larger objects in the same families, indicating that collisional evolution has not altered them as heavily as expected. You could imagine a scenario where getting knocked around and fragmented would change the surface composition, and then you would see a different surface color for tiny TNOs compared to their larger siblings. So it’s really fascinating to see that the smallest objects are somehow ‘remembering’ and preserving the history of how they were made,
said Anastasia Morgan, a Northern Arizona University PhD candidate who led the study of color and composition.
Cold and Hot Populations Retain Ancient Signatures
The research teams analyzed two distinct dynamical populations among these distant bodies. The dynamically cold
TNOs maintain relatively circular orbits along the original plane of the solar system, while the dynamically hot
TNOs follow highly elliptical paths after being scattered outward during the early migration of the outer gas giants.
Co-author David Trilling emphasized that these objects preserve a unique window into the past, noting that these dynamically ‘hot’ TNOs retain a signature of where they were born, even though they’ve been orbitally scrambled since then.
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