We've discovered 27 new bodies beyond Neptune. They could tell us how our Solar System began

We've discovered 27 new bodies beyond Neptune. They could tell us how our Solar System began

Hubble and JWST reveal surprisingly unaltered billion-year-old icy bodies

Get monthly inspiration to your door with BBC Sky At Night Magazine - subscribe today
Astronomers using NASA's Spitzer Space Telescope have gathered the most detailed data yet on a gap in a protoplanetary, or planet-forming, disk surrounding a young star.
Astronomers using NASA's Spitzer Space Telescope have gathered the most detailed data yet on a gap in a protoplanetary, or planet-forming, disk surrounding a young star. This artist's concept illustrates one interpretation of the data, which attributes the disk gap to planet formation. At the center lies a young star that is pulling in material from an inner disk of dust and gas. The gap between this inner disk and the thick outer disk is believed to be occupied by developing gas giant planets. The putative planets prevent the outer disk material from naturally falling in toward the star, thereby creating the gap. The inner disk is roughly the size of our inner solar system, or the distance between the Sun and Jupiter. The gap would span orbits equivalent to those of Jupiter and Saturn. The Saturn-like rings around the planets hint that they are very young and still surrounded by debris left over from their own formation. (Note: the planets in this illustration are exaggerated in size.) At the edges of the solar system, the thick disk is expected to coalesce into asteroids, comets and possibly more planets. The bipolar flow, or dim jets of material, shooting out of the star's north and south poles, is a characteristic typical of young stars that are not yet fully formed.

Jamie Middleton

Some of the smallest objects in the outer Solar System appear to have preserved clues to how they formed billions of years ago, despite expectations that collisions should have altered them.

Astronomers combined observations from the Hubble Space Telescope and James Webb Space Telescope to study 27 newly discovered trans-Neptunian objects (TNOs), small, icy bodies orbiting beyond Neptune.

Some are the faintest, tiniest objects ever directly observed, at just 5km (3 miles) across. The results provide a new look at planetesimals, the building blocks of planets. 

They expected the smallest TNOs to show more evidence of collisions than larger objects.

Read more

An artist's impression of the hypothetical Planet 9.
An artist's impression of the hypothetical Planet 9.

Researchers say the tiny trans-Neptunian objects ‘remember’ how they formed. Credit: NASA, ESA, Leah Hustak (STScI)

Repeated impacts should have broken up their surfaces and mixed their materials, producing different colours and compositions.

Instead, the small objects largely follow the same colour relationships seen among much larger TNOs.

Because colour provides clues to surface composition, this suggests their surfaces have changed surprisingly little.

They also uncovered fewer tiny TNOs than some models of planet formation predict.

“It’s really fascinating to see that the smallest objects are somehow ‘remembering’ and preserving the history of how they were made,” says lead author Anastasia Morgan of Northern Arizona University.

The team are now planning deeper observations. Future JWST observations could search for TNOs as small as 1km (0.6 miles) across, potentially providing an even clearer picture of how the Solar System’s planetary building blocks formed.
Author avatar

Jamie Middleton

Commissioning Editor

Jamie Middleton is a seasoned science journalist and BBC Sky at Night Magazine's Commissioning Editor.
Footer banner
This website is owned and published by Our Media Ltd. www.ourmedia.co.uk
© Our Media 2026