Hubble and Webb telescopes uncover insights into early solar system

These distant objects offer a unique window into the materials that contributed to planet formation. Most are incredibly faint, requiring exceptional observational capabilities to detect – shining more than 100 million times less brightly than objects visible to the naked eye. Two studies, published in The Astronomical Journal, analyzed the new discoveries to understand their sizes, compositions, and histories.

Scientists believe planets formed from dust and pebbles accumulating into larger bodies called planetesimals. These planetesimals eventually coalesced into the planets we observe today. However, many objects beyond Neptune did not fully develop into planets, preserving a record of the solar system’s early formation.

Research teams from the University of Victoria in Canada, the National Research Council of Canada, and Northern Arizona University conducted the most extensive survey of TNOs to date. Hubble captured visible light while Webb observed in infrared, allowing researchers to analyze color, estimate size, and map orbital paths. Color provides clues about surface composition, acting like a fingerprint of an object’s history.

The study focused on two groups of TNOs: dynamically “cold” and “hot” objects. Cold objects remain in their original formation regions, following circular paths close to the planets’ orbital plane. Hot objects have experienced more chaotic histories, scattered outward by the shifting giant planets, resulting in elongated orbits.

Surprisingly, despite their differing histories, both populations showed similar surface characteristics, even in the smallest objects. Scientists had anticipated that smaller TNOs would display evidence of frequent collisions, altering their surfaces. Instead, the newly discovered objects exhibited color patterns similar to their larger counterparts, suggesting fewer impacts than initially predicted.

“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 Anastasia Morgan, a Northern Arizona University PhD candidate.

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

The observations also revealed a surprising lack of very small TNOs compared to predictions from some planet formation models. The James Webb Space Telescope’s sensitivity allowed scientists to detect 27 exceptionally faint objects, one so dim it would be akin to spotting fireflies on the Moon from Earth. The smallest object measured just 3 miles (5 kilometers) across.

Marielle Eduardo, a University of Victoria PhD candidate, noted, “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.”