article · The Astrophysical Journal
Research based on 28 stellar occultations of the large trans-Neptunian object (50000) Quaoar, combined with nine previously published events, has precisely determined its physical characteristics. Quaoar was found to have an oblate ellipsoid shape, with equatorial semiaxes of approximately 566 km and a polar semiaxis of about 511 km, resulting in an equivalent volumetric diameter of 1094.4 km. The study also established a geometric albedo of 0.125 and new upper limits for the surface pressure of a methane atmosphere, at 0.15 nbar (1 sigma). A density of 1.760 g cm−3 was calculated, which is compatible with Quaoar being in a Maclaurin hydrostatic equilibrium state, supporting its eligibility as a dwarf planet.
Understanding the precise physical properties, such as size, shape, and density, of distant trans-Neptunian objects like Quaoar provides crucial insights into the formation and evolution of our solar system. It also helps refine the classification of celestial bodies, contributing to our knowledge of planetary science.
The abstract describes fundamental research in planetary science and does not indicate any direct application pathways, potential users, or commercialisation opportunities.
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Abstract We present results from 28 stellar occultations by the large trans-Neptunian object (50000) Quaoar registered between 2018 and 2025. By performing a joint analysis of this occultation dataset, along with nine other published events, we were able to fit an oblate ellipsoid shape, with equatorial semiaxes a and b of 566 . 1 − 2.2 + 2.5 km, and a polar semiaxis, c , of 511 . 2 − 3.7 + 3.6 km. It provides an equivalent volumetric diameter of 1094.4 ± 4.6 km and polar oblateness of 0.097 ± 0.011. Considering an absolute magnitude of H = 2.79 ± 0.35, we derive a geometric albedo of p V = 0.125 ± 0.038. We have derived new upper limits to the surface pressure of a CH 4 atmosphere of 0.15 nbar (1 σ ) and 0.65 nbar (3 σ ). We also provide a table with the 36 new astrometric positions for Quaoar. Using the new system mass derived from Weywot’s orbit around Quaoar, we calculated a density of 1.760 ± 0.109 g cm −3 . Moreover, from the derived size and rotation period (8.8394 ± 0.0002 hr, we calculated that, if Quaoar is in Maclaurin hydrostatic equilibrium state, it would have a density of 1.859 ± 0.200 g cm −3 . This result, within the error bars, is compatible with the value we found. Therefore, this work shows that Quaoar can be a Maclaurin object, being eligible as a dwarf planet.
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DOI: 10.3847/1538-4357/ae907e
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