Plutino

This article is about objects in a 2:3 orbital resonance with Neptune; they are not to be confused with plutoids or plutons.

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 "plutoids"

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.

Orbits

Some of the first known plutinos compared in size, albedo and colour

Origin

It is thought that objects that are currently in mean orbital resonances with Neptune initially followed independent heliocentric paths. As Neptune migrated outward early in the Solar System's history (see origins of the Kuiper belt), the bodies it approached would have been scattered; during this process, some of them would have been captured into resonances. The 3:2 resonance is the strongest and most stable among all resonances. This is the main reason it contains the largest number of bodies.

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 perihelia inside (or close to) the orbit of Neptune and aphelia 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 × Neptune's orbital period), varying by at most a few years from this value.

Unusual plutinos include:

• 2005 TV₁₈₉, which follows the most highly inclined orbit (34.5°)
• (15875) 1996 TP₆₆, which has the most elliptical orbit (its eccentricity is 0.33), with the perihelion halfway between Uranus and Neptune
• 2007 JH₄₃ following a quasi-circular orbit
• 2002 VX₁₃₀ lying almost perfectly on the ecliptic (inclination less than 1.5°)

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 the orbits of plutinos with an eccentricity 10%–30% smaller or larger than that of Pluto are not stable over Ga timescales.

Orbital diagrams

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  The motions of Orcus and Pluto in a rotating frame with a period equal to Neptune's orbital period (holding Neptune stationary.)

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  Orbits and sizes of the larger plutinos (and the reference non-plutino 2002 KX14). Orbital eccentricity is represented by segments extending horizontally from perihelion to aphelion; inclination is shown on the vertical axis.

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  The distribution of plutinos (and the reference non-plutino 2002 KX14). Small inserts show histograms for the distributions of orbital inclination and eccentricity.

Brightest objects

The 10 brightest plutinos include:

Name	Semi-major axis, AU	Perihelion, AU	Inclination, °	(H)	Size, km	Mass, 1020 kg	Albedo	V–R	Discovery year	Discoverer
Pluto	39.3	29.7	17.1	−0.7	2322	130	0.49–0.66		1930	Clyde Tombaugh
Orcus	39.2	30.3	20.6	2.3	850 ± 90	6.32 ± 0.05	0.28 ± 0.06	0.37	2004	M. Brown, C. Trujillo, D. Rabinowitz
(208996) 2003 AZ84	39.4	32.3	13.6	3.8	910 ± 60	~5	0.07 ± 0.02	0.36	2003	M. Brown, C. Trujillo
Ixion	39.7	30.1	19.6	3.8	650+250 −220	~3	0.12+.14 −.06	0.61	2001	Deep Ecliptic Survey
(84922) 2003 VS2	39.3	36.4	14.8	4.4	725 ± 200	~3	0.058+.04 −.02	0.59	2003	NEAT
2003 UZ413	39.2	30.4	12.0	4.4	~600	~2	?	?	2001	M. Brown, C. Trujillo, D. Rabinowitz
2002 XV93	39.3	34.5	13.3	4.7	~ 560	~ 1.5	~0.09	0.37	2001	M.W.Buie
38628 Huya	39.4	28.5	15.5	5.2	532 ± 25	~1	0.05+0.005 −0.004	0.65	2000	Ignacio Ferrin
2001 QF298	39.3	34.9	22.4	5.3	~500	~1	~0.09	?	2001	Marc W. Buie
(47171) 1999 TC36	39.3	30.6	8.4	5.4	414 ± 38	0.1275 ± 0.0006	0.07 ± 0.01	0.65	1999	E. P. Rubenstein, L.-G. Strolger
(55638) 2002 VE95	39.4	30.4	16.3	5.8	~380	~0.5	~0.09	0.71	2002	NEAT

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
• Minor Planet Center Orbit database (MPCORB) as of 2008-10-05.
• Minor Planet Circular 2008-S05 (October 2008) Distant Minor planets was used for orbit classification.

External links

• David Jewitt on Plutinos
• Minor Planet Center, List of TNOs
• MPC List of Distant Minor Planets