The curiously warped mean plane of the kuiper belt

Kathryn Volk, Renu Malhotra

Research output: Contribution to journalArticlepeer-review

43 Scopus citations


We measured the mean plane of the Kuiper Belt as a function of semimajor axis. For the classical Kuiper Belt as a whole (the nonresonant objects in the semimajor axis range 42-V48 au), we find a mean plane of inclination im 1°.8+0°7 -0°4 and longitude of ascending node Ωm = 77°+18° -14° (in the J2000 ecliptic-equinox coordinate system), in accord with theoretical expectations of the secular effects of the known planets. With finer semimajor axis bins, we detect a statistically significant warp in the mean plane near semimajor axes 40-V42 au. Linear secular theory predicts a warp near this location due to the v18 nodal secular resonance; however, the measured mean plane for the 40.3-V42 au semimajor axis bin (just outside the v18) is inclined ~13° to the predicted plane, a nearly 3σ discrepancy. For the more distant Kuiper Belt objects of semimajor axes in the range 50-V80 au, the expected mean plane is close to the invariable plane of the solar system, but the measured mean plane deviates greatly from this: it has inclination im= 9°.1+6°6 -3°8 and longitude of ascending node Ωm= 227°+18° -44°. We estimate this deviation from the expected mean plane to be statistically significant at the ~97%-V99% confidence level. We discuss several possible explanations for this deviation, including the possibility that a relatively close-in (a ≲ 100 au), unseen, small planetary-mass object in the outer solar system is responsible for the warping.

Original languageEnglish (US)
Article number62
JournalAstronomical Journal
Issue number2
StatePublished - Aug 2017


  • Kuiper belt
  • celestial mechanics
  • general

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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