James Webb and Hubble Space Telescopes Discover 27 New Distant Objects Beyond Neptune

For billions of years, the smallest and faintest bodies in the solar system have lingered in darkness far beyond the orbit of Neptune. Invisible to backyard telescopes and difficult to resolve even with modern instruments, these distant icy worlds offer a rare, undisturbed archive of how planets first coalesced. Now, researchers have harnessed the combined muscle of two premier observatories to bring these remote objects into sharper focus, uncovering unexpected patterns in how the outer solar system was assembled.

Joint Hubble and Webb Observations Target 27 Far-Flung Trans-Neptunian Objects

In a coordinated campaign, scientists pointed NASA’s Hubble and James Webb Space Telescopes simultaneously at a single patch of sky to study 27 newly discovered bodies. The targets range in distance from approximately 30 to over 100 astronomical units from the sun. One astronomical unit equals about 93 million miles, or 150 million kilometers, placing these objects billions of miles away from Earth. Because direct imaging of such faint targets is exceedingly difficult, researchers paired Hubble’s visible-light sensitivity with Webb’s infrared power. By tracking how these faint specks of light moved against background stars over time, the teams determined their orbits, sizes, colors, and surface properties.

The survey represents the deepest look at Trans-Neptunian Objects to date. Among the 27 newly identified bodies, some measure roughly 5 kilometers, or about 3 miles wide. One object proved so faint that its brightness is equivalent to standing on Earth and spotting a small swarm of fireflies on the Moon.

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Cold and Hot Populations Retain Primordial Surface Properties

The coordinated observations examined two distinct categories of Trans-Neptunian Objects. The first group consists of dynamically cold TNOs resting on nearly circular orbits in the flat plane of the solar system, largely undisturbed since their formation. The second group comprises dynamically hot TNOs that formed between the current paths of Uranus and Neptune before being scattered outward into highly elliptical orbits when the outer gas giants migrated during the solar system’s infancy.

Astronomers previously theorized that small TNOs in both populations would show the physical scars of continuous impacts over eons. The common assumption was that repeated collisions would strip away primordial outer layers, exposing fresh interior ice and altering surface colors compared to larger family members. Instead, the data revealed that tiny TNOs share the same surface properties and color relationships as their larger counterparts, suggesting that collisions are not changing the surfaces significantly.

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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.

Anastasia Morgan, Northern Arizona University PhD candidate

Co-author David Trilling of Northern Arizona University noted that these dynamically hot bodies retain a signature of where they were born despite being orbitally scrambled during planetary migration.

Size Distributions Defy Traditional Planet Formation Models

In addition to surface color, Webb data allowed researchers to evaluate the physical dimensions of the newly spotted bodies. The findings demonstrated that overall size distributions remain remarkably consistent across both the hot and cold populations, pointing to a uniform building process across different regions of the early solar system.

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It’s very interesting that the process of planetesimal formation ends up producing the same distribution of sizes for both cold and hot populations, despite forming in different regions of the early solar system.

Marielle Eduardo, University of Victoria PhD candidate

Despite these consistent size ratios, the survey detected fewer very small bodies than certain established planet formation models had predicted. The findings were detailed in two complementary papers published in The Astronomical Journal by research teams led by PhD candidates from the University of Victoria under the guidance of the National Research Council of Canada, alongside researchers from Northern Arizona University.