Hubble and Webb Reveal Surprising Preservation of Distant Solar System Objects

Using the combined capabilities of the Hubble Space Telescope and the James Webb Space Telescope (JWST), astronomers have identified 27 new Trans-Neptunian Objects (TNOs) orbiting well beyond Neptune. The study, led by PhD candidates Anastasia Morgan of Northern Arizona University and Marielle Eduardo of the University of Victoria, reveals that these diminutive bodies—ranging from 6 to 25 miles (10 to 40 kilometers) in diameter—retain surface compositions that appear unchanged since the dawn of the solar system.

According to traditional models, TNOs should have suffered extensive collisions that altered their surface materials, resulting in distinct colors compared to larger counterparts. However, observations indicate the opposite: even the smallest objects seem to “remember” their formation history. “It’s really fascinating to see that the smallest objects are somehow ‘remembering’ and preserving the history of how they were made,” Morgan stated.

The research highlights a distinction between dynamically “cold” TNOs, which orbit near the ecliptic plane in near-circular paths, and dynamically “hot” TNOs, which were likely ejected from the region between Uranus and Neptune into the scattered disk. Despite the gravitational scrambling experienced by the hot population, both groups show remarkably similar surface properties. David Trilling of Northern Arizona University noted, “These dynamically hot TNOs retain a signature of where they were born, even though they’ve been orbitally scrambled since then.”

This preservation presents a dilemma for astronomers: either impacts in the outer solar system are far less frequent than predicted, or the collisions do not disrupt surface compositions as expected. Additionally, JWST’s infrared observations allowed Eduardo to determine accurate sizes independent of surface reflectivity, revealing fewer small TNOs than formation models anticipate.

“The process seems to be insensitive to disk conditions, producing similar planetesimal sizes whether the disk is hot or cold, and dense or fluffy,” Eduardo explained. The findings were published on September 8 in The Astronomical Journal, marking the deepest survey yet conducted beyond Neptune.