Size, Shape, Density, and Atmospheric Limit of (50000) Quaoar Revealed from 14 years of Stellar Occultation
ASTROPHYSICAL JOURNAL, vol.1008, no.2, 2026 (SCI-Expanded, Scopus)
- Publication Type: Article / Article
- Volume: 1008 Issue: 2
- Publication Date: 2026
- Doi Number: 10.3847/1538-4357/ae907e
- Journal Name: ASTROPHYSICAL JOURNAL
- Journal Indexes: Science Citation Index Expanded (SCI-EXPANDED), Scopus, INSPEC, zbMATH, Directory of Open Access Journals, Academic Search Ultimate (EBSCO)
- Open Archive Collection: AVESIS Open Access Collection
- Istanbul University Affiliated: Yes
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 pV = 0.125 +/- 0.038. We have derived new upper limits to the surface pressure of a CH4 atmosphere of 0.15 nbar (1 sigma) and 0.65 nbar (3 sigma). 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.