Quaoar is an icy world in the Kuiper belt, the zone of small, icy bodies beyond Neptune. It is about 1,090 kilometers (680 miles) across on average, a little less than half the width of Pluto. Quaoar has a moon, Weywot, and two rings that lie much farther out than rings are expected to survive.

Size

Quaoar's size is measured by watching it pass in front of distant stars, an event called a stellar occultation. Each observer who sees a star blink out records one line, or chord, across Quaoar's shadow. Many chords from different places trace its outline.

A 2026 study, released before peer review, combined 37 occultations and found that Quaoar is slightly flattened. It is about 1,132 kilometers across its equator and 1,022 kilometers from pole to pole, the same volume as a sphere 1,094 kilometers across. A 2024 study that combined the occultation shape with the heat Quaoar gives off found a diameter of 1,090 kilometers, give or take about 40 kilometers.

The first measurement, made with the Hubble Space Telescope in 2002, gave about 1,300 kilometers. It was the first time a Kuiper belt object had been seen as a disk rather than a point of light, but it overestimated the size by about a fifth.

Size comparisons

If Quaoar were shrunk to the size of a basketball, its outer ring would form a circle about 1.8 meters (6 feet) across, a little more than the height of a person 1.7 meters tall.
Charon, Pluto's largest moon and the next larger round world in the explorer, is 1,212 kilometers across, about 11% wider than Quaoar.
Sedna, another distant icy world, is about 995 kilometers across, a little smaller than Quaoar.
Pluto is about 2.2 times as wide as Quaoar.

Rings where they should not be

The rings were found the same way as Quaoar's size, from brief dips in a star's light as a ring passed in front of it. The outer ring was detected in occultations between 2018 and 2021. It circles about 4,057 kilometers from Quaoar's center, more than seven times Quaoar's own radius. An occultation on August 9, 2022, revealed a second, fainter ring about 2,520 kilometers from the center.

Both rings lie outside a boundary called the Roche limit, which for Quaoar is about 1,780 kilometers from its center. Beyond that limit, ring particles are expected to clump together into moons in less than 100 years. One proposed explanation is that Quaoar's ring particles bounce off each other more than those in Saturn's rings do, instead of sticking together.

Weywot, Quaoar's moon, orbits about three times as far out as the outer ring. From Weywot's orbit, astronomers can work out Quaoar's mass, and from that its density. In 2025, astronomers reported a second, much smaller moon, detected once during an occultation.

Discovery, orbit and surface

Chad Trujillo and Mike Brown discovered Quaoar in 2002 with the Oschin Schmidt telescope at Palomar Observatory. At the time, it was the largest object found orbiting the Sun since Pluto in 1930. They named it after a creation god of the Tongva people, the original inhabitants of the Los Angeles Basin. The name is pronounced "kwa-whar."

Quaoar circles the Sun on a nearly round orbit about 44 times as far out as Earth. The James Webb Space Telescope has found water ice, carbon dioxide ice and frozen methane and ethane on its surface. It is not one of the five dwarf planets the International Astronomical Union recognizes as of 2026, but the 2026 study found that its shape and spin fit a body shaped by its own gravity, which would make it eligible.

Sources

Size, shape, density, and atmospheric limit of (50000) Quaoar revealed from 14 years of stellar occultation. Margoti et al., arXiv preprint, 2026.
The visible and thermal light curve of the large Kuiper belt object (50000) Quaoar. Kiss et al., Astronomy and Astrophysics, 2024.
The two rings of (50000) Quaoar. Pereira et al., Astronomy and Astrophysics, 2023.
Orbital Characterization of a Newly Discovered Small Satellite Around Quaoar. Proudfoot et al., The Astrophysical Journal Letters, 2025.
A Tale of 3 Dwarf Planets: Ices and Organics on Sedna, Gonggong, and Quaoar from JWST Spectroscopy. Emery et al., Icarus, 2024.
Hubble Spots an Icy World Far Beyond Pluto. NASA, 2002.
Pluto and the Developing Landscape of Our Solar System. International Astronomical Union.
Pluto Fact Sheet. NASA, 2024.
Official Basketball Rules 2026: Basketball Equipment. FIBA, 2026.

Report a Problem

for Quaoar