The mass and density of the dwarf planet (225088) 2007 OR10

Csaba Kiss*, Gábor Marton, Alex H. Parker, Will M. Grundy, Anikó Farkas-Takács, John Stansberry, Andras Pál, Thomas Müller, Keith S. Noll, Megan E. Schwamb, Amy C. Barr, Leslie A. Young, József Vinkó

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

3 Citations (Scopus)


The satellite of (225088) 2007 OR10 was discovered on archival Hubble Space Telescope images and along with new observations with the WFC3 camera in late 2017 we have been able to determine the orbit. The orbit's notable eccentricity, e ≈ 0.3, may be a consequence of an intrinsically eccentric orbit and slow tidal evolution, but may also be caused by the Kozai mechanism. Dynamical considerations also suggest that the moon is small, Deff < 100 km. Based on the newly determined system mass of 1.75 ·1021 kg, 2007 OR10 is the fifth most massive dwarf planet after Eris, Pluto, Haumea and Makemake. The newly determined orbit has also been considered as an additional option in our radiometric analysis, provided that the moon orbits in the equatorial plane of the primary. Assuming a spherical shape for the primary this approach provides a size of 1230 ± 50 km, with a slight dependence on the satellite orbit orientation and primary rotation rate chosen, and a bulk density of 1.75 ± 0.07 g cm−3 for the primary. A previous size estimate that assumed an equator-on configuration (1535−225 +75 km) would provide a density of 0.92−0.14 +0.46 g cm−3, unexpectedly low for a 1000 km-sized dwarf planet.

Original languageEnglish
Pages (from-to)3-10
Number of pages8
Early online date21 Mar 2019
Publication statusPublished - Dec 2019
Externally publishedYes


  • Asteroids: General
  • Kuiper belt objects: Individual ((225088) 2007OR)
  • Methods: Observational
  • Minor planets
  • Techniques: Photometric

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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