Far beyond the orbit of Neptune, a population of tiny, frozen worlds is preserving clues about the earliest days of our Solar System.

For the first time, astronomers have combined observations from NASA’s Hubble Space Telescope and the James Webb Space Telescope to study some of the smallest and faintest known objects in the outer Solar System. The observations are giving scientists a new look at the ancient building blocks from which planets formed.

These distant objects are known as Trans-Neptunian Objects (TNOs). They orbit the Sun beyond Neptune and are so faint that many are more than 100 million times dimmer than objects visible to the unaided eye.

Tiny Survivors From the Early Solar System

When the Solar System was young, a disk of dust and pebbles surrounded the newborn Sun. Over time, these particles collided and stuck together, eventually forming larger bodies called planetesimals.

Planetesimals were the building blocks that eventually came together to create planets, moons, asteroids and other larger objects.

But beyond Neptune, the process stopped before these bodies could grow into full-sized worlds.

As a result, the distant region beyond Neptune contains a population of frozen planetesimals that may preserve some of the original material from the Solar System’s formation billions of years ago.

Hubble and Webb Work Together

The new observations involved looking at the same region of sky with both space telescopes.

Hubble observed the objects in visible light, while Webb examined them in infrared wavelengths.

This combination allowed researchers to investigate the objects’ colors, compositions, sizes and orbits.

Scientists studied 27 newly discovered, extremely faint TNOs, including objects that are among the smallest ever directly observed at these distances.

One of the smallest objects detected has a diameter of only about 3 miles (5 kilometers).

That is roughly five times smaller than the size of TNOs that can normally be detected using the most sensitive ground-based telescopes.

Two Different Populations

The researchers studied two major groups of TNOs known as “cold” and “hot” populations.

Cold TNOs generally travel on relatively circular orbits that remain close to the plane of the Solar System. Scientists believe many of these objects have remained relatively close to their original locations.

Hot TNOs are different. They are thought to have formed closer to the Sun, between the present-day orbits of Uranus and Neptune, before gravitational interactions with the giant planets pushed them farther outward.

Today, these objects generally travel on more elongated orbits and can move well above or below the Solar System’s main plane.

The Objects Still Carry Their Ancient Colors

One of the most surprising discoveries came from studying the colors of these tiny worlds.

Scientists expected frequent collisions between small TNOs to significantly alter their surfaces. If that were happening, the smallest objects should have looked different from their larger relatives.

Instead, the researchers found that the small TNOs generally follow the same color relationships as the larger objects in their respective populations.

In other words, their surfaces appear to have preserved important characteristics from their formation.

This suggests that collisions may have been less destructive than previously expected, or that some TNOs have managed to preserve their original, pre-collision material.

The finding is particularly interesting for the dynamically “hot” objects. Although their orbits have been dramatically rearranged over the Solar System’s history, their surfaces still appear to retain clues about where they were born.

Fewer Tiny Objects Than Expected

Webb also provided scientists with information about how many objects exist at different sizes.

Researchers found that the size distributions of the hot and cold populations were surprisingly similar, even though the two groups formed in different regions of the early Solar System.

The observations also revealed fewer very small TNOs than some planet-formation models predicted.

This could provide an important clue about how planetesimals originally formed.

If similar size distributions developed under very different conditions, it may indicate that the process of planetesimal formation was less dependent on the environment of the early Solar System than scientists previously thought.

A Fossil Record of Planet Formation

The distant TNO population can be thought of as a kind of fossil record of Solar System formation.

Unlike the planets, which experienced billions of years of geological and atmospheric evolution, many of these small icy bodies have remained relatively isolated in the Solar System’s outer regions.

Studying them allows astronomers to investigate a stage of planetary evolution that is difficult to observe anywhere else.

The fact that some of these tiny objects appear to preserve their original surface characteristics makes them particularly valuable for understanding how the first planetary building blocks formed.

Hubble and Webb Reveal More Together

Neither telescope could provide exactly the same information on its own.

Hubble’s sensitivity in visible light and Webb’s powerful infrared capabilities complement each other, allowing scientists to detect and characterize objects that are extraordinarily faint and distant.

The study demonstrates how combining observations from different wavelengths can reveal details about objects that would otherwise remain almost invisible.

And these tiny worlds may have something important to tell us.

They are remnants of a much younger Solar System — and despite billions of years of orbital changes and collisions, some of them still appear to “remember” how they were made.

The Bigger Picture

The discovery gives astronomers another way to investigate one of the biggest questions in planetary science: How did the Solar System’s first solid building blocks come together to eventually create worlds like Earth?

By studying the smallest surviving objects beyond Neptune, researchers can work backward through time and reconstruct the conditions that existed when our planetary system was still taking shape.

The outer Solar System may therefore be more than a collection of distant icy objects. It could be one of the best places to look for the ancient fingerprints of planet formation.

Source: NASA, September 8, 2026.