Hubble and Webb Uncover Solar System Relics Preserving 4.5 Billion-Year-Old Origins

New insights from NASA’s Hubble Space Telescope and James Webb Space Telescope reveal that some of the tiniest bodies located beyond Neptune have retained characteristics from the early solar system, providing fresh clues about how planets formed billions of years ago.

The collaborative study examined trans-Neptunian objects (TNOs), icy small-scale entities orbiting past Neptune that stand among the faintest directly observed targets. Despite expectations that these ancient objects would show effects of frequent collisions and surface weathering, the smallest TNOs exhibit striking similarities to their larger counterparts.

Results from two reports in the Astronomical Journal detail the analysis of colors, materials, sizes, and orbits of 27 newly identified small TNOs. Findings indicate these distant bodies may preserve chemical traces from the era when the earliest building blocks of planets coalesced.

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Revisiting the Frozen Origins of Our Solar System

The region beyond Neptune contains a collection of icy remnants that have endured since the solar system’s infancy. These objects are relics from a time when dust and tiny particles around the newborn Sun clumped together to form larger bodies called planetesimals, which would eventually serve as the foundations for planets.

Unlike the inner solar system where planetesimals combined into planets and moons, the outer zones have preserved many of these objects in nearly unchanged states. Studying TNOs offers direct insights into the materials and mechanisms that shaped our system over 4 billion years ago.

For this project, teams from the University of Victoria in Canada and Northern Arizona University leveraged the complementary capabilities of both telescopes. Hubble captured visible light to assess color data, while Webb used infrared to examine faint objects and accurately estimate their dimensions.

The scientists investigated two TNO categories: the dynamically “cold” TNOs, which follow near-circular orbits close to the solar system’s original plane, and the dynamically “hot” TNOs, believed to have formed near Uranus and Neptune before migrating outward during giant planet movements.

Small TNOs Maintain Ancient Color Signatures

Contrary to expectations that smaller TNOs would appear distinct due to repeated impacts altering their surfaces, the study found their colors closely match those of larger TNOs. This suggests their surfaces have remained largely unchanged since formation.

“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. So it’s really fascinating to see that the smallest objects are somehow ‘remembering’ and preserving the history of how they were made,” said Northern Arizona University Ph.D. candidate Anastasia Morgan, who led the study of color and composition.

Published in two accompanying papers in the Astronomical Journal, the research demonstrates that even dynamically “hot” TNOs retain clues to their formation locations despite significant orbital reshuffling over the solar system’s lifetime.

“These dynamically ‘hot’ TNOs retain a signature of where they were born, even though they’ve been orbitally scrambled since then,” commented co-author David Trilling from Northern Arizona University.

This new understanding indicates that the outer solar system may have experienced fewer surface-altering collisions than some theories predicted or that these bodies possess mechanisms to maintain their original chemical makeup over billions of years.

Webb’s Infrared Vision Reveals Surprising Size Distributions

The advanced infrared observations from the James Webb Space Telescope enabled researchers to precisely measure the sizes of distant TNOs, unveiling unexpected patterns: both cold and hot populations display similar size ranges.

These findings challenge earlier models predicting that different formation zones in the early solar system would produce distinct size distributions among planetesimals.

Instead, the data imply that planetesimal formation processes yielded comparable size outcomes across the various early solar system environments, regardless of local temperature or density.

“It’s remarkable that planetesimals from both cold and hot populations formed with similar size distributions, despite originating under very different disk conditions—whether hot, cold, dense, or tenuous,” explained University of Victoria Ph.D. candidate Marielle Eduardo, who led the investigation of size characteristics.

Additionally, fewer extremely small TNOs were detected than prior formation theories anticipated. Among the Webb discoveries was an object only about 3 miles (5 kilometers) in diameter—a size too small to be observed by many earlier surveys.

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