Quaoar had one “impossible” ring, then astronomers found two

Scientists still don’t fully understand how dust and gas in the early solar system coalesced into moons and planets.

Like the first ring around Quaoar, which was announced in February by a team of astronomers, the second ring lies beyond what is known as the Roche Limit. Material orbiting close to this distance tends to be torn apart by tidal forces. Thus, a ring within Roche’s boundary would tend to remain a ring, while a ring of debris outside Roche’s boundary would normally coalesce into a moon.

For Quaoar, Roche’s limit was calculated to be 1,100 miles. The second ring, at a distance of 1,500 miles from Quaoar’s center, is even closer than the ring announced in February, which has a radius of about 2,500 miles.

Quaoar (pronounced KWA-wahr, the name of the creator deity of the Tongva natives who live around Los Angeles) orbits the Sun in the Kuiper Belt, a region of frozen debris beyond Neptune that includes Pluto.

The ring is not visible in telescope images. Instead, astronomers found it indirectly, when distant stars passed behind Quaoar, blocking out the starlight. From 2018 to 2021, Quaoar passed in front of four stars, and astronomers on Earth were able to observe shadow eclipses, also known as stellar eclipses.

They also noticed some dimming in the starlight before and after the star’s flash, indicating the presence of the first ring.

Another occultation occurred on August 9 of last year, and astronomers once again pointed telescopes, large and small, at Quaoar in hopes of learning more about the ring.

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The new observations revealed more details including a narrow, dense core in the ring just a few miles wide, which is surrounded by more dispersed enveloped material. The notes also revealed the second episode.

Another disappearance will occur on May 13, visible to telescopes in the United States and Canada.

“This event includes a bright star and will be useful to better constrain the shape of the Quaoar, as well as a good opportunity to get more details on these two remarkable rings,” said Mr. Pereira.

A possible explanation for Quaoar’s distant rings is the presence of the moon Weywot. The moon may have caused gravitational perturbations that prevented ring particles from accumulating on additional moons. Both rings occur at locations close to what is known as resonance with Weywot, and the resonance may turn out to be more important than the Roche limit for determining whether rings turn into moons or remain rings.

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