Plutino

This article is about objects in a 2:3 orbital resonance with Neptune; it is not to be confused with the proposed but rejected IAU term, Plutonian object.

Types of distant minor planets

Cis-Neptunian objects Centaurs Neptune trojans Trans-Neptunian objects (TNOs)‡ Kuiper belt objects (KBOs) Classical KBOs (Cubewanos) Resonant KBOs Plutinos (2:3 Resonance) Scattered disc objects (SDOs) Resonant SDOs Detached objects Oort cloud objects (OCOs)

‡ Trans-Neptunian dwarf planets are called "plutoids"

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.

Orbits

Origin

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.

Orbital characteristics

File:TheKuiperBelt 60AU LargePlutinos.svg

This diagram compares the sizes and orbits of the larger plutinos.¹ The largest, Pluto, Orcus and Ixion, are represented by white circles. The eccentricity of the orbits is represented by red segments (extending from perihelion to aphelion) and the inclination is represented on the vertical axis. (Pluto's moon Charon is omitted; its size is similar to that of Orcus). To illustrate the range of orbits, three smaller plutinos with 'extreme' orbits are plotted in yellow.
¹For the few large objects whose diameters are known with some precision, the current estimates are shown. For all others, the size of the object plotted is proportional to their absolute magnitude, assuming the albedo.

File:TheKuiperBelt 60AU Plutinos distribution.svg

This diagram plots the distribution of all known plutinos (153 as of February, 2006). Small inserts show histograms for orbital inclinations ('i', at 5^o intervals) and eccentricity ('e' at 0.05 intervals).

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^o 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 (40^o)
• 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 0.5^o).

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

• David Jewitt (Univ. of Hawaii) on Plutinos
• Minor Planet Center, List of TNOs
• MPC List of Distant Minor Planets

References

• 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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