Planetary rings are observed around giant planets, small bodies and dwarf planets. Until now, all known dense rings have been close enough to their parent bodies where tidal forces prevent material of reasonable density from coalescing into a satellite.

In a new study, a large team of international scientists using HiPERCAM – a sensitive camera developed by scientists at the University of Sheffield – has discovered a new ring system in our solar system. The team has found a new ring system around a dwarf planet, Quaoar, at the edge of the solar system.

Quaoar is a Pluto-sized dwarf planet orbiting Neptune. This trans-Neptunian object has an estimated radius of 555 km and possesses a satellite of about 80 km orbiting with 24 Quaoar rays.

The rings are too small and faint to see directly in a photo. Instead, they discovered rings by tracking an occultation, which occurs when Quaoar obscures the light of a background star as it orbits the sun. The event lasted less than a minute, but two unexpected dips of light that appeared to be part of a ring system surrounding Quaoar came before and after.

What makes the ring system unique is that it lies more than seven planetary radii away — twice as far away as what was previously considered the maximum radius according to the so-called “Roche limit,” the outer limit of what was thought to be that ring systems could survive.

new ring system
Credit: Instituto de Astrofisica de Andalucia

By comparison, Saturn’s main rings are within three planetary radii. Therefore, hypotheses about ring formation need to be re-examined in light of this discovery.

Professor Vik Dhillon, a co-author of the study from the University of Sheffield’s Department of Physics and Astronomy, said: “It was unexpected to discover this new ring system in our solar system, and it was doubly unexpected to find the rings so far from Quaoar, challenging our previous understandings of how such rings form. Our high-speed camera – HiPERCAM – was key to this discovery, as the event lasted less than a minute and the rings are too small and faint to see in a direct image.

“Everyone learns about Saturn’s beautiful rings when they’re a kid, so hopefully this new find will provide more insight into how they formed.”

Magazine reference:

  1. Morgado, BE, Sicardy, B., Braga-Ribas, F. et al. A dense ring of the trans-Neptunian object Quaoar beyond its Roche limit. Nature 614, 239-243 (2023). DOI: 10.1038/s41586-022-05629-6