Quaoar
What is Quaoar?
Dwarf planets· Diameter 1,090 km. An icy Kuiper belt world on a nearly circular 289-year orbit. It has two rings far from its surface, where theory says rings should not survive — a puzzle for astronomers.
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.
Quaoar's rings that refuse to clump
Close to a body, its gravity pulls small grains apart, so they cannot gather together and stay as a ring. Farther out than a certain distance, however, the grains are expected to pull on each other and clump into a moon. This boundary is called the Roche limit, and Saturn's bright main rings all lie inside it.
A study announced in February 2023 challenged this rule. Astronomers had recorded starlight each time Quaoar passed in front of a star between 2018 and 2021, and the light dimmed briefly about 4,100 km from Quaoar's centre. A ring was orbiting more than seven Quaoar radii out, far beyond the Roche limit. Later that year a second ring was confirmed at about 2,500 km.
Why the rings do not clump is still uncertain. Grains in the outer ring go around once for every three turns of Quaoar on its axis. At a spot with a matching rhythm like this, the grains keep getting stirred, which may stop them from gathering. Some researchers think the moon Weywot's rhythm plays a part as well.
The dwarf planet in depth
Quaoar was discovered in 2002 by Chad Trujillo and Michael Brown. It is named after the creator god of the Tongva people of the Los Angeles area. When it was found, it was the largest object discovered in the solar system since Pluto. It is about 1,090 km across.
Quaoar moves between 42 and 45 AU from the Sun and takes 289 years to go around once. Unlike Pluto's stretched orbit, Quaoar's is nearly a circle. Kuiper belt bodies on such orbits are called 'classical' objects; they are thought to circle close to where they formed, without being pushed around much by Neptune.
Quaoar has a moon, Weywot, found by the Hubble Space Telescope in 2007. It is about 200 km across and goes around Quaoar every 12.4 days. Its name is that of the sky god who is Quaoar's son in Tongva myth. The moon's orbit allowed Quaoar's mass to be worked out: its density is about 1.75 times that of water, suggesting a rocky core wrapped in an icy shell.
Frequently asked
- How big is Quaoar?
- The diameter of Quaoar is ~1,090 km.
- How far is Quaoar from Earth?
- The distance of Quaoar is 42~45 AU.
- What is notable about Quaoar?
- The note of Quaoar is two rings outside the Roche limit.
Related
Figures are representative approximations. Simulated positions use J2000 mean elements.