A new ring system has been discovered around a dwarf planet, called Quaoar, which is about half the size of Pluto and orbits the sun beyond Neptune.

The ring system orbits much farther out than normal for other ring systems, calling into question current theories about how ring systems form.

Rings around a dwarf planet, Quaoar
The discovery, published in Nature, was made by an international team of astronomers using HiPERCAM, an extremely sensitive high-speed camera developed by scientists at the University of Sheffield that is mounted on the world’s largest optical telescope, the Gran Telescopio Canarias de 10.4 meters in diameter (GTC) on La Palma.

The rings are too small and faint to see directly in an image. Instead, the researchers made their discovery by observing an occultation, when Quaoar blocked the light from a background star as it orbited the sun. The event lasted less than a minute, but was unexpectedly preceded and followed by two dips in light, indicative of a ring system around Quaoar.

Quaoar’s rare rings
Ring systems are relatively rare in the solar system. Besides the well-known rings around the giant planets Saturn, Jupiter, Uranus, and Neptune, only two other minor planets possess rings: Chariklo and Haumea. All previously known ring systems can survive because they orbit close to the main body, so tidal forces prevent ring material from building up and forming moons.

What makes the ring system around Quaoar remarkable is that it is located at a distance of more than seven planetary radii, double what was thought to be the maximum radius according to the so-called “Roche limit”, which is the limiting outer radius of where ring systems were thought to survive. For comparison, the main rings around Saturn are within three planetary radii. Therefore, this discovery has forced us to rethink ring formation theories.

Professor Vik Dhillon, 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 doubly unexpected to find the rings so far out in Quaoar, defying our “Previous notions of how those rings form. Using 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 directly.”

Reference

Bruno Morgado, A dense ring of the trans-Neptunian object Quaoar outside its Roche limit, Nature (2023). DOI: 10.1038/s41586-022-05629-6. www.nature.com/articles/s41586-022-05629-6