The ring was discovered by telltale dips in brightness before and after Quaoar passed in front of distant stars
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Astronomers have discovered a ring around the dwarf planet Quaoar, one of over 100,000 small planetesimals in the outer reaches of the Solar System, in the Kuiper belt beyond the orbit of Pluto. Ground-based telescope, and the space observatory Cheops observed Quaoar as it passed in front of a succession of stars. The ring was discovered as the distant star blinked out before and after the occultation by the dwarf planet. About 3,000 trans-Neptunian objects are known, with Pluto and Eris being the largest and well known ones. The small sizes and the extreme distances from the Sun makes it a challenge to study these remote worlds.
ESA’s star mapping mission Gaia, which continuously tracks the movements of millions of stars in the Milky Way, has improved scientific understanding of the movements of stars, allowing astronomers to predict exactly when stellar occultations are likely to take place. This has enabled astronomers in turn to study more occultations. Recently, the James Webb Space Telescope discovered a ring around the asteroid 10199 Chariklo, while it passed in front of a distant star. Astronomers used the data from ESA’s Gaia instrument for that observation as well. It is likely that the increased observations of occultations will also increase the detections of ring systems.
Astronomer Bruno Morgado says, “When we put everything together, we saw drops in brightness that were not caused by Quaoar, but that pointed to the presence of material in a circular orbit around it. The moment we saw that we said, ‘Okay, we are seeing a ring around Quaoar.” The ring system around Quaoar is unusual because the ring is outside the Roche limit, the distance at which a body approaching a world will disintegrate under the influence of the gravity of the world, overcoming the gravity of the body itself. Ring systems are only expected to exist within the Roche limit. The icy temperatures at the extreme distances are suspected to play a role in the formation of the ring.