In astronomy, a plutino is a trans-Neptunian object in 2:3 mean motion resonance with Neptune. Plutinos are named after Pluto, which follows an orbit trapped in the same resonance, with the Italian diminutive suffix -ino. The name refers only to the orbital resonance and does not imply common physical characteristics; it was invented to describe those bodies smaller than Pluto with the resonance (hence the diminutive) but now includes Pluto itself.

Plutinos form the inner part of the Kuiper belt and represent about a quarter of the known Kuiper Belt objects (KBOs). Aside from Pluto itself, the first plutino, 1993 RO, was discovered on September 16, 1993.

The largest plutinos include Pluto, 90482 Orcus, 28978 Ixion, 38083 Rhadamanthus, and 38628 Huya.



It is thought that objects that are currently in mean orbital resonances with Neptune followed initially independent heliocentric paths. During Neptune’s migration (see Kuiper Belt), the objects have been caught into the resonances sweeping outward.[1]

Orbital characteristics

File:TheKuiperBelt 60AU LargePlutinos.svg
File:TheKuiperBelt 60AU Plutinos distribution.svg

While the majority of plutinos have low orbital inclinations, a substantial number of them follow orbits similar to that of Pluto, with inclinations in the 10-25o range and eccentricities around 0.2-0.25, resulting in perihelions inside (or close to) the orbit of Neptune and aphelions close to the main Kuiper belt's outer edge (where objects have 1:2 resonance with Neptune).

The orbital periods of plutinos cluster around 247.3 years (1.5 x Neptune's orbital period), varying by at most a few years from this value.

Unusual plutinos include:

  • 2005 EK298, which follows the most highly inclined orbit of a plutino (40o)
  • 2003 QV91, which has the most elliptical orbit of a plutino (its eccentricity is 0.35, with the perihelion halfway between Uranus and Neptune and the aphelion well into the scattered disk region).
  • 2002 KX14, which has a quasi-circular orbit (its eccentricity is 0.04), lying almost perfectly on the ecliptic (inclination less than 0.5o).

See also the comparison with the distribution of the cubewanos.

Long-term stability

The gravitational influence of Pluto is usually neglected given its small mass. However, the resonance width (the range of semi-axes compatible with the resonance) is very narrow and only a few times larger than Pluto’s Hill sphere (gravitational influence). Consequently, depending on the original eccentricity, some Plutinos will be driven out of the resonance by interactions with Pluto. Numerical simulations suggest that Plutinos with the eccentricity 10%-30% smaller or bigger than that of Pluto are not stable in Ga timescales.[2]

External links


  1. Malhotra The Origin of Pluto's Orbit: Implications for the Solar System Beyond Neptune Astronomical Journal, 110 (1995), p420. Preprint in arXiv
  2. Qingjuan Yu and Scott Tremaine The Dynamics of Plutinos The Astronomical Journal, 118 (1999), pp. 1873–1881 Preprint in arXiv
  • D.Jewitt, A.Delsanti The Solar System Beyond The Planets in Solar System Update : Topical and Timely Reviews in Solar System Sciences , Springer-Praxis Ed., ISBN 3-540-26056-0 (2006). Preprint of the article (pdf)
  • Bernstein G.M., Trilling D.E., Allen R.L. , Brown K.E , Holman M., Malhotra R. The size Distribution of transneptunian bodies. The Astronomical Journal, 128, 1364-1390. preprint on arXiv (pdf)
  • Minor Planet Circular 2005-X77 Distant Minor planets was used for plutinos' orbits classification. The updated data can be found in MPC 2006-D28.
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