Quaoar
What is Quaoar?
Dwarf planets· Diameter 1,090 km. An icy Kuiper belt world on a nearly circular 289-year orbit, with a moon, Weywot, and two rings sitting far beyond where rings should be able to survive — a puzzle for astronomers. Named for the Tongva creator god; see its round orbit in the orbit view.
The orbit of Quaoar at this moment: https://nowsky.org/solar/orbit?fw=quaoar&sp=110 — replayed live, no login.
Orbit and size
| Diameter | ~1,090 km |
|---|---|
| Distance | 42~45 AU |
| Year | 289 yr |
| Note | two rings outside the Roche limit |
Figures are representative approximations. Source: compiled from NASA and IAU public data.
Frequently asked
- How big is Quaoar?
- ~1,090 km.
- How far is Quaoar from Earth?
- 42~45 AU.
- What is notable about Quaoar?
- two rings outside the Roche limit.
The size debate — from Hubble's 1,260 km to 1,110 km by occultation
Right after its discovery in 2002, Quaoar became the first Kuiper-belt object whose disk Hubble resolved directly, giving a diameter of 1,260 km — at the time the largest body found since Pluto, and a candidate "tenth planet". But the measurement sat at the edge of Hubble's angular resolution and carried a large error, and a stellar occultation in 2013 brought the diameter down to 1,110 km.
An occultation measures the size of the shadow by timing how long a star is hidden at several sites as the object passes in front, with errors of only tens of kilometres. Combined with the orbit of the moon Weywot, that diameter gives Quaoar a density twice that of water, rock-rich for a Kuiper-belt body. The same method found two rings in 2023, orbiting seven Quaoar radii out — a distance at which theory says they should have clumped into moons — and they remain a puzzle.
The dwarf planet in depth
Quaoar was discovered in 2002 by Chad Trujillo and Michael Brown and named for the creator god of the Tongva people of the Los Angeles area. At the time it was the largest solar-system body found since Pluto; its diameter is about 1,090 km. It follows a nearly circular orbit between 42 and 45 AU, completing a lap every 289 years.
Hubble found its moon Weywot, the Tongva sky god, in 2007. Then in 2023 a stellar occultation revealed a ring — at seven Quaoar radii, well outside the Roche limit where ring particles should clump into a moon. Why the ring survives is an open problem, and a second, inner ring has since been confirmed. Crystalline water ice and ammonia hydrate on its surface hint at past cryovolcanism.
Track Quaoar in the orbit view and, unlike Pluto's stretched ellipse, you will see an almost perfectly round path — a textbook example of the orbits followed by the 'classical' members of the Kuiper belt.
Related
Figures are representative approximations. Simulated positions use J2000 mean elements.