Scientists have discovered a new ring system around a dwarf planet at the edge of the Solar System. The ring system orbits much farther than is typical of other ring systems, challenging current theories of how ring systems form.
The ring system is around a dwarf planet called Quaoar, which is about half the size of Pluto and orbits the Sun behind Neptune. 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, which is mounted on the world’s largest optical telescope, the 10.4-metre Gran Telescopio. Canarias (GTC) to La Palma.
The rings are too small and faint to be seen directly in the image. Instead, scientists made their discovery by observing an eclipse, when light from a background star is blocked by Quaoar as it orbits the Sun. The event lasted less than a minute, but was unexpectedly preceded and followed by two drops of light, indicating a ring system around Quaoar.
Ring systems are relatively rare in the Solar System – as well as the well-known rings around the giant planets Saturn, Jupiter, Uranus and Neptune, only two other smaller planets – Chariklo and Haumea – have rings. All previously known ring systems are able to survive because they orbit close to the parent body, so tidal forces prevent the ring material from accreting and forming moons.
What makes the ring system around Quaoar remarkable is that it lies at a distance of more than seven planetary radii – twice as far as what was previously thought to be the maximum radius according to the so-called ‘Roche limit’, the outer limit of where assumed that circular systems were able to survive. By comparison, the main rings around Saturn lie within three planetary radii. This discovery therefore forced a re-evaluation of 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 rings so far away. from Quaoar, challenging our previous ideas about how such rings form. The use of our high-speed camera — HiPERCAM — was key to this discovery because the event lasted less than one minute and the rings are too small and faint to see a direct image.
“Everyone learns about Saturn’s beautiful rings when they’re a child, so hopefully this new discovery will provide further insight into how they formed.” 59 academics from around the world participated in the study, led by the Federal University of Rio de Janeiro, Brazil. The research was part-funded by the Science and Technology Facilities Council (STFC) and involved six UK universities – Sheffield, Edinburgh, St Andrews, Warwick, Birmingham and the Open University.
