TL;DR: NASA's Hubble and Webb telescopes jointly studied 27 newly found Trans-Neptunian Objects and found the tiniest ones keep the same colors as larger bodies, preserving clues to planet formation.

First Joint Hubble-Webb Survey Goes Deep Beyond Neptune

For the first time, scientists used the joint power of NASA's Hubble and James Webb Space Telescopes to study some of the most far-flung bodies in our solar system, Trans-Neptunian Objects, according to NASA Science.

The project examined 27 newly discovered tiny, dim Trans-Neptunian Objects, or TNOs, in what researchers described as the deepest TNO survey to date.

Results appeared in two complementary papers published Tuesday in The Astronomical Journal, according to NASA Science.

The release describing the work is identified as Release ID 2026-018 from the Space Telescope Science Institute, dated September 08, 2026 at 10:00AM EDT.

NASA Science reported that some of the objects are among the smallest and faintest ever directly seen.

These objects are typically small, faint, icy bodies orbiting the Sun beyond the orbit of Neptune, according to NASA Science.

Most are more than 100 million times dimmer than objects visible to the unaided eye, according to NASA Science.

The Space Telescope Science Institute summary described the work as offering the best view yet into an early stage of planet-building.

Why Tiny Frozen Worlds Matter for Planet Building

This class of small bodies offers the best view into an early stage of planet-building, when a disk of dust and pebbles in orbit around the Sun coalesced into city-sized "planetesimals," according to NASA Science.

Planetesimals are described as the solid building blocks that clump together to form planets, according to NASA Science.

Beyond Neptune, this second stage of merging into full-sized worlds never happened, leaving behind a frozen population of planetesimals, according to NASA Science.

The NAU Review reported that TNOs hold some of the history of the formation and evolution of the outer solar system.

In that university account, Northern Arizona University Ph.D. candidate Anastasia Morgan said TNOs tell researchers what was present at the beginning.

Morgan also said in the NAU Review account that TNOs give clues into how other planetary systems are formed.

The two university teams examined a patch of sky simultaneously with Hubble and Webb, according to NASA Science.

Hubble observed the TNOs' visible light, while Webb observed their infrared light, according to NASA Science.

The NAU Review similarly reported that Morgan and her colleagues studied TNOs in one tiny patch of sky using Hubble for visible light and Webb for infrared light.

Who Led the Two-Team Effort

In the deepest TNO survey to date, teams led by PhD candidates from the University of Victoria in Canada, under the guidance of the National Research Council of Canada, and Northern Arizona University in Flagstaff examined the target field, according to NASA Science.

The color and composition study was led by Northern Arizona University PhD candidate Anastasia Morgan, according to NASA Science.

The size-distribution study was led by University of Victoria PhD candidate Marielle Eduardo, according to NASA Science.

The NAU Review reported that Morgan's study was published Sept. 8 in The Astronomical Journal alongside a complementary study led by Eduardo.

The combined optical-near-infrared paper lists authors including Anastasia N. Morgan, Marielle R. Eduardo, David E. Trilling, Wesley C. Fraser, John Stansberry, G. M. Bernstein, B. Hilbert, Matthew J. Holman, W. M. Grundy, Kevin J. Napier, S. C. Tegler and Cesar I. Fuentes, with affiliations including Northern Arizona University, University of Victoria, Space Telescope Science Institute, Center for Astrophysics Harvard & Smithsonian, University of Michigan and University of Chile, according to the journal abstract record.

The same abstract record identifies funding support from the Space Telescope Science Institute, the National Aeronautics and Space Administration, the National Science Foundation and Agencia Nacional de Investigación y Desarrollo.

The teams measured the objects' colors, which are like a fingerprint of the surface composition, as well as their sizes and determined their orbits, according to NASA Science.

Cold and Hot Populations Tell Different Origin Stories

In the coordinated observations, the teams studied two different types of TNOs, according to NASA Science.

The first, dynamically "cold" TNOs, are on their original, relatively circular orbits around the Sun in the plane of the solar system, according to NASA Science.

The second type, dynamically "hot" TNOs, formed between the current locations of Uranus and Neptune but were pushed outward where they are today when the outer gas giants migrated early in the solar system's history, according to NASA Science.

Today the hot population resides in highly elliptical orbits and moves in and out of the plane of our solar system, according to NASA Science.

The journal abstract for the color study describes the small cold classical discoveries as occupying a single reflectance color sequence previously identified for larger cold classical TNOs, with no evidence for a change in that sequence at smaller sizes.

In contrast, the dynamically excited TNOs discovered in that sample exhibit a broader range of colors consistent with multiple compositional classes seen at larger sizes, according to the same abstract.

Co-author David Trilling of Northern Arizona University said the dynamically "hot" TNOs retain a signature of where they were born, even though they have been orbitally scrambled since then, according to NASA Science.

The NAU Review account similarly quoted Trilling saying the objects retain a signature of where they were born despite scrambled orbits.

NASA Science reported that both the "hot" and "cold" populations seem to keep the same colors as when they were formed, with little change since the birth of the solar system.

Smallest Objects 'Remember' How They Were Made

Prior to these observations, astronomers thought that small TNOs from both hot and cold populations would have undergone many collisions, changing their surfaces compared to larger TNOs, according to NASA Science.

That is not what the observations showed, according to NASA Science.

Instead, the small bodies look like their larger counterparts, according to NASA Science.

This implies that collisions are not changing the surfaces significantly — perhaps because there are fewer collisions than expected, or because the TNOs somehow retain their primordial, pre-collision compositions, according to NASA Science.

The teams are still trying to unravel this mystery, according to NASA Science.

Morgan and her colleagues expected to find lots of variation in the TNOs' colors, shapes and materials, evidence that the objects have been traveling and colliding for eons, according to the NAU Review.

What they found instead was very little variation, suggesting much less movement than they imagined, according to the NAU Review.

"For these objects to have a lot of the same color and shape, it's telling us that they have probably sat there and not been very collisionally active," Morgan said in the NAU Review account.

The same account quoted Morgan saying models say the objects should have been altered by collisions, but that is not what the team is seeing.

"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," Morgan said, according to NASA Science. "So it's really fascinating to see that the smallest objects are somehow 'remembering' and preserving the history of how they were made."

How Faint, How Small, How Similar

Webb discovered 27 new, remarkably dim TNOs, one so faint it is equivalent to standing on Earth and seeing a small swarm of fireflies on the Moon, according to NASA Science.

The NAU Review gave the same comparison, quoting Morgan as asking readers to imagine standing on Earth and trying to measure a swarm of fireflies on the Moon without magnification.

The smallest object observed has a diameter of about 3 miles, or 5 kilometers, which is about five times smaller than what is possible to detect with the most sensitive ground-based telescopes, according to NASA Science.

The Webb data also allowed researchers to measure the number of objects of each size, according to NASA Science.

They found that the overall size distributions for both hot and cold populations were surprisingly similar, according to NASA Science.

"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," Eduardo said, according to NASA Science.

Eduardo added that the process seems to be insensitive to disk conditions, producing similar planetesimal sizes whether the disk is hot or cold, and dense or fluffy, according to NASA Science.

Researchers also found fewer of these very small bodies than they expected based on some planet formation models, according to NASA Science.

The Space Telescope Science Institute summary stated that researchers unexpectedly found fewer small TNOs than they expected.

How Hubble Plus Webb Made the Measurement Possible

This project would not have been possible without Hubble and Webb working together to detect and characterize these TNOs, according to NASA Science.

With Hubble's sensitivity in visible light and Webb's in infrared, the space telescopes provide more insights than either can on its own, according to NASA Science.

The journal abstract reported coordinated and nearly simultaneous observations from Webb and Hubble, with Webb's NIRCam providing detections and near-infrared photometry for faint TNOs and Hubble's ACS and WFC3 imaging enabling recovery in the optical.

Thirteen Webb-detected TNOs were recovered in the Hubble observations, and trailed point-spread-function photometry was used to derive mean magnitudes, colors and rotational lightcurves, according to the journal abstract.

Together the data yielded optical-to-near-infrared colors spanning 0.35 to 3.2 microns, according to the journal abstract.

Lightcurve amplitudes were generally low for both dynamical groups in the sample, according to the journal abstract.

The object 2015 GK56, a previously known TNO in the field, displays a large-amplitude, structured lightcurve consistent with a contact binary, according to the journal abstract.

The abstract concluded that the characteristic color distribution of TNOs extends to smaller sizes than previously studied, suggesting a primordial origin rather than size-dependent collisional processing.

The Hubble Space Telescope has been operating for over three decades and continues to make discoveries that shape understanding of the universe, according to NASA Science.

Hubble is a project of international cooperation between NASA and ESA, the European Space Agency, according to NASA Science.

NASA's Goddard Space Flight Center in Greenbelt, Maryland, manages the telescope and mission operations, according to NASA Science.

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