About the image. Drawn as a reddish icy world with a thin outer ring and its moon Weywot. The rings were found by watching starlight flicker and have never been seen directly; their brightness and the surface are imagined, and the inner ring is left out.
Quaoar was discovered on 4 June 2002 by Chad Trujillo and Mike Brown at Palomar Observatory. It was named after the creator god of the Tongva, the people native to the Los Angeles area. About 1 100 kilometres across, it is one of the larger worlds of the Kuiper belt, and for twenty years it seemed fairly ordinary.
A ring in the wrong place
In 2023 a team led by Bruno Morgado reported in Nature that Quaoar has a ring. Nobody photographed it. Instead, telescopes on the ground and in space watched as Quaoar passed in front of distant stars. Just before and after the star vanished behind Quaoar itself, its light briefly dimmed: something thin was circling the dwarf planet.
The surprise was the ring’s distance. Every planet has a Roche limit: inside it, tides tear loose material apart and it stays a ring; outside it, the material is expected to clump together into a moon. All known dense rings, Saturn’s included, lie inside this limit. Quaoar’s ring sits about 4 057 kilometres from its centre, more than twice its Roche limit, yet it has not formed a moon. It lies near a resonance with Quaoar’s spin, which may help keep it spread out, but exactly why it survives is still being studied.
A second, fainter ring closer in, at 2 520 kilometres, was announced later the same year.
Weywot
Quaoar has a moon, Weywot, discovered in 2006 and named after a son of Quaoar in Tongva tradition. Recent measurements put it at about 146 kilometres across. Its orbit, 12.4 days long, gives Quaoar’s mass: about 1.21 × 10²¹ kilograms.
Quaoar circles the Sun on a nearly round orbit between about 42 and 45 AU, taking about 285 years. Its surface holds water ice, small amounts of methane and ethane, and carbon dioxide.
How far out it would be
Quaoar goes around once every 285 years, at 43.335 AU from its star. Dashed circles show Jupiter, Saturn and Neptune around the Sun, on the same scale.
Earth days passing: 0
Your weight on Quaoar
On Quaoar
Gravity there is about 0.03× Earth's. Calculated from the measured mass and radius.
Gallery
A small reddish-brown cratered world inside a wide, bright white ring, with the Sun as a small star in the corner, an impression of the dwarf planet Quaoar and its ring. AI-generated painting.A broad stream of glittering ice particles sweeping across the foreground and curving away towards a small reddish world in the distance, an impression of the ring of Quaoar. AI-generated painting.Quaoar, 3D artist's impression, rendered from the interactive model.Quaoar, 3D artist's impression, from another angle, rendered from the interactive model.Quaoar, 3D artist's impression, close-up, rendered from the interactive model.
Timeline
2002Discovered on 4 June at Palomar Observatory.
2006Its moon Weywot is found.
2023A ring far outside the Roche limit is reported in Nature; a second ring follows.
Questions people ask
Does Quaoar have rings?
Yes, two. The outer one lies more than twice as far out as the Roche limit, where rings were thought unable to survive.
How big is Quaoar?
About 1 116 km across, roughly half the size of Pluto.
Does Quaoar have a moon?
Yes, Weywot, about 146 km across, orbiting every 12.4 days.