Direct measurement of the size of the large Kuiper belt object (50000) Quaoar

Michael E. Brown, Chadwick A. Trujillo

Research output: Contribution to journalArticlepeer-review

64 Scopus citations


We imaged the recently discovered bright Kuiper belt object (50000) Quaoar with the Hubble Space Telescope High Resolution Camera to directly determine its size. The point-spread function (PSF) of each of 16 images was carefully measured from a field star 13″ from Quaoar, and the expected PSF at the location of Quaoar was convolved with Quaoar's motion vector and a model resolved disk. A least-squares analysis was performed to find the best-fit disk size. The apparent diameter of Quaoar was resolved as 40.4 ± 1.8 milliarcseconds. Accounting for the uncertainty due to an unknown limb-darkening function, the size of Quaoar is 1260 ± 190 km with red and blue albedos of 0.092-0.023+0.036 and 0.101 -0.024+0.039, respectively. These albedos are significantly higher than the canonically assumed value of 4%. Quaoar is the largest currently known minor planet.

Original languageEnglish (US)
Pages (from-to)2413-2417
Number of pages5
JournalAstronomical Journal
Issue number4 1780
StatePublished - Apr 2004
Externally publishedYes


  • Minor planets, asteroids
  • Techniques: image processing

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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