Hubble and Webb Reveal Surprising Secrets About Tiny Worlds Beyond Neptune

A collaborative observation campaign pairing the James Webb Space Telescope with the Hubble Space Telescope has unveiled new details about the icy, ancient bodies orbiting in the farthest reaches of our solar system. By focusing on 27 previously elusive Trans-Neptunian Objects (TNOs), researchers have gained a rare glimpse into the primordial building blocks that shaped the planets we see today.

The findings, detailed in two papers published September 8, 2026, in The Astronomical Journal, challenge long-held assumptions regarding how these small, frozen remnants of the solar system’s infancy have evolved over billions of years.

Clues to a Pristine Past

TNOs are categorized into two primary groups: “cold” objects, which reside in relatively stable, circular orbits near the solar system’s plane, and “hot” objects, which were displaced into highly inclined, distant paths during the early, turbulent migration of the giant planets. Scientists hypothesized that smaller TNOs would show evidence of frequent, violent collisions, which should have resurfaced them and altered their color profiles compared to their larger counterparts.

However, the combined infrared data from Webb and visible-light imagery from Hubble revealed a surprising consistency. The smallest objects, some measuring as little as 10 kilometers across, displayed color patterns nearly identical to the larger bodies. This suggests that the outer solar system may be a more tranquil environment than previously modeled, or that surface impacts are simply not as effective at altering the chemical makeup of these icy, distant worlds.

“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,” explained Anastasia Morgan of Northern Arizona University, who spearheaded the study’s analysis of composition and color.

Furthermore, the “hot” population of TNOs appears to have retained a distinct chemical signature linked to their original birthplaces, even after the chaotic migration of the giant planets tossed them into new orbital territories. David Trilling, also of Northern Arizona University, noted that these objects act as time capsules, preserving the conditions of the early solar system rather than being entirely transformed by their subsequent history.

Peering Into the Deep Kuiper Belt

To reach these faint, distant targets, the research team utilized the advanced survey capabilities of Webb’s NIRCam, which measured object sizes with greater accuracy by bypassing the reflective surface biases that complicate visible-light observations. By employing a “shift-and-stack” imaging technique, the team identified bodies as small as 10 kilometers, marking the most profound look into this population to date.

The study, led by Marielle Eduardo, revealed a lower count of extremely small TNOs than many formation models predicted. Curiously, both the “cold” and “hot” populations exhibited similar size distributions, pointing toward a universal process of planetesimal formation that occurred consistently across the early solar disk, regardless of local environmental variations.

“It’s very interesting that the process of planetesimal formation ends up producing the same distribution of sizes for both cold and hot populations,” Eduardo remarked. By integrating data across a wavelength range of 0.35 to 3.2 micrometers, the team has established new constraints on how the outer solar system evolved, offering a clearer picture of the processes that transition a chaotic cloud of debris into a structured planetary system.

The research, published in The Astronomical Journal, underscores the power of international collaboration in space exploration, as these instruments continue to push the boundaries of what is observable in the dark, frigid reaches of the Kuiper Belt.