Astrologers Shed Light on Quaoar's Astonishing Ring System
The Story
Astronomers using ESA's Cheops space telescope discovered a ring system around Quaoar, a distant dwarf planet orbiting beyond Neptune, at a surprising location far outside the body's Roche limit.
The Roche limit marks the boundary within which tidal forces should keep material from clumping into a moon, so finding a dense ring well past it, at roughly 7.5 times Quaoar's radius, overturns long held assumptions.
Under conventional theory such material should have gathered into a moon within decades, yet the ring persists at this greater distance.
Researchers detected it through stellar occultations recorded between 2018 and 2021, moments when Quaoar passed in front of distant stars, marking the first time a trans Neptunian object was observed this way from space.
The team combined Cheops data with ground based telescopes and citizen scientists to confirm the finding, which appeared in Nature in 2023.
One leading idea holds that the extreme cold at Quaoar's distance may keep icy particles from sticking together during collisions, opening fresh questions about how rings form and endure across the solar system.
The Roche limit marks the boundary within which tidal forces should keep material from clumping into a moon, so finding a dense ring well past it, at roughly 7.5 times Quaoar's radius, overturns long held assumptions.
Under conventional theory such material should have gathered into a moon within decades, yet the ring persists at this greater distance.
Researchers detected it through stellar occultations recorded between 2018 and 2021, moments when Quaoar passed in front of distant stars, marking the first time a trans Neptunian object was observed this way from space.
The team combined Cheops data with ground based telescopes and citizen scientists to confirm the finding, which appeared in Nature in 2023.
One leading idea holds that the extreme cold at Quaoar's distance may keep icy particles from sticking together during collisions, opening fresh questions about how rings form and endure across the solar system.
Why It Matters
Quaoar keeps embarrassing ring theory. A second ring, Q2R, turned up in 2022 Gemini North data at 2,520 km, still outside the 1,780 km Roche limit, and on June 25, 2025 two California observers caught a 1.23 second blackout from something else: most likely a 38 km moon on a 3.6 day orbit, per Sci.News. Resonances with Weywot and Quaoar's spin, not cold sticky ice, now carry the burden of explaining why nothing clumps, and Webb sees no trace of the moon. The loser is the tidy Roche rule for small bodies. Rubin Observatory logged 380 candidate objects beyond Neptune in under two months, per Sky & Telescope, and Quaoar stays well placed for occultations for another 10 years.
Go Deeper
Read the original reporting at ESA.
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