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| ‡ 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.
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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.[1] 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.
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:
See also the comparison with the distribution of the cubewanos.
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.[2] 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.[3]
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 |
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