In astronomy, a plutino is a trans-Neptunian object in 2:3 mean motion resonance with Neptune. For every 2 orbits that a Plutino makes, Neptune orbits 3 times. 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 (hence the diminutive) following similar orbits. The class includes Pluto itself and its moons.

Plutinos form the inner part of the Kuiper belt and represent about a quarter of the known Kuiper Belt objects (KBOs). Plutinos are the largest class of the resonant trans-Neptunian objects (i.e. bodies in orbital resonances with Neptune).

Aside from Pluto itself and Charon, the first plutino, 1993 RO, was discovered on September 16, 1993.

The largest plutinos include Pluto, 90482 Orcus, 28978 Ixion, (84922) 2003 VS2, 38628 Huya, and 2003 AZ84.



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

Orbital characteristics

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 10-25° 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:

  • , which follows the most highly inclined orbit of a plutino (34.5°)
  • , which has the most elliptical orbit of a plutino (its eccentricity is 0.33, with the perihelion halfway between Uranus and Neptune and the aphelion well into the scattered disk region).
  • , which has a quasi-circular orbit (its eccentricity is 0.04), lying almost perfectly on the ecliptic (inclination less than 0.5°).

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.

External links


  • 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
  • Minor Planet Circular 2005-X77 Distant Minor planets was used for plutinos' orbits classification. The updated data can be found in MPC 2006-D28, MPEC 2006-X45 and MPEC 2008-O05

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