These observations reveal that icy bodies in the outer solar system are scarcer than some planet formation models predicted, while their surface colors indicate they may preserve traces of their origins despite billions of years of potential collisions.
Detecting Faint TNOs With Hubble and Webb
Spotting objects in the outermost reaches of the solar system requires immense observational power. According to the study findings, TNOs are frequently more than 100 million times dimmer than objects visible to the unaided human eye. One newly identified body was so faint that researchers compared detecting it to standing on Earth and spotting a small swarm of fireflies on the Moon. The smallest measured roughly 3 miles, or 5 kilometers, across, making it about five times smaller than sizes detectable by the most sensitive ground-based telescopes.
The joint survey utilized simultaneous observations of the same patch of sky. Hubble captured visible light, while Webb recorded infrared data. Together, these instruments allowed the science teams to calculate orbits, estimate physical sizes, and measure surface colors. The research efforts were led by doctoral candidates at the University of Victoria in Canada and Northern Arizona University in Flagstaff, operating under the guidance of the National Research Council of Canada.
Did you know? Trans-Neptunian objects are icy remnants left over from the material that originally built the planets. Studying the smallest among them helps researchers piece together how planetary construction began.
Comparing Cold and Hot Populations Beyond Neptune
The survey analyzed two distinct dynamical groups of TNOs that experienced different origins and orbital evolutions. Dynamically “cold” TNOs maintain relatively circular orbits close to the plane of the planets. Conversely, dynamically “hot” TNOs formed between the current locations of Uranus and Neptune before giant planet migration pushed them outward into elongated orbits.
Webb’s data demonstrated that both groups share similar size distributions, meaning the proportional numbers of small and large bodies follow much the same pattern. University of Victoria PhD candidate Marielle Eduardo noted that planetesimal formation appears largely insensitive to disk conditions, producing similar sizes whether the original disk was hot, cold, dense, or fluffy.
Surface Composition and Collision History
Color measurements collected by the research teams provided insight into what these bodies experienced after formation. Astronomers previously hypothesized that small TNOs in both orbital groups would undergo repeated collisions that altered their surface compositions, resulting in color profiles distinct from larger objects.
Instead, the data showed that small TNOs match the color relationships of their larger siblings.
Frequently Asked Questions
What are trans-Neptunian objects?
TNOs are small, icy bodies orbiting the Sun at distances beyond the orbit of Neptune. They are remnants from the early era of planet formation.
How did telescopes spot such small objects?
Researchers combined simultaneous observations from NASA’s Hubble Space Telescope (measuring visible light) and James Webb Space Telescope (measuring infrared light) to detect objects down to 3 miles across.
Why do surface colors matter?
Surface colors provide clues about composition. Finding that small TNOs share the colors of larger objects suggests that collisions have not substantially changed their surface compositions.
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