Plutino
In astronomy, the plutinos are a dynamical group of trans-Neptunian objects that orbit in 2:3 mean-motion resonance with Neptune. This means that for every two orbits a plutino makes, Neptune orbits three times. The dwarf planet Pluto is the largest member as well as the namesake of this group. Plutinos are named after mythological creatures associated with the underworld.
Plutinos form the inner part of the Kuiper belt and represent about a quarter of the known Kuiper belt objects. They are also the most populous known class of resonant trans-Neptunian objects . Aside from Pluto itself, the first plutino, 1993 RO, was discovered on September 16, 1993.
Orbits
Origin
It is thought that the objects that are currently in mean orbital resonances with Neptune initially followed a variety of independent heliocentric paths. As Neptune migrated outward early in the Solar System's history, 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 a low-order resonance and is thus the strongest and most stable among all resonances. This is the primary reason it has a larger population than the other Neptunian resonances encountered in the Kuiper Belt. The cloud of low-inclination bodies beyond 40 AU is the cubewano family, while bodies with higher eccentricities and semimajor axes close to the 3:2 Neptune resonance are primarily plutinos.Orbital characteristics
While the majority of plutinos have relatively low orbital inclinations, a significant fraction of these objects follow orbits similar to that of Pluto, with inclinations in the 10–25° range and eccentricities around 0.2–0.25; such orbits result in many of these objects having perihelia close to or even inside Neptune's orbit, while simultaneously having aphelia that bring them close to the main Kuiper belt's outer edge.The orbital periods of plutinos cluster around 247.3 years, varying by at most a few years from this value.
Unusual plutinos include:
- , which follows the most highly inclined orbit
- , which has the most elliptical orbit, with the perihelion halfway between Uranus and Neptune
- following a quasi-circular orbit
- lying almost perfectly on the ecliptic
Long-term stability
Pluto's influence on the other plutinos has historically been neglected due to its relatively small mass. However, the resonance width is very narrow and only a few times larger than Pluto's Hill sphere. Consequently, depending on the original eccentricity, some plutinos will eventually 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
Brightest objects
The plutinos brighter than HV=6 include:| Object | a | q | i | H | Diameter | Mass | Albedo | V−R | Discovery year | Discoverer | Refs |
| 134340 Pluto | 39.3 | 29.7 | 17.1 | −0.7 | 2322 | 130 | 0.49–0.66 | 1930 | Clyde Tombaugh | ||
| 90482 Orcus | 39.2 | 30.3 | 20.6 | 0.37 | 2004 | M. Brown, C. Trujillo, D. Rabinowitz | |||||
| 39.4 | 32.3 | 13.6 | ≈ 3 | 2003 | M. Brown, C. Trujillo | ||||||
| 28978 Ixion | 39.7 | 30.1 | 19.6 | ≈ 3 | 0.61 | 2001 | Deep Ecliptic Survey | ||||
| 39.5 | 31.3 | 13.6 | ≈ 380–680 | ? | ? | ? | 2017 | D. J. Tholen, S. S. Sheppard, C. Trujillo | |||
| 39.3 | 36.4 | 14.8 | ≈ 1.5 | 2003 | NEAT | ||||||
| 39.2 | 30.4 | 12.0 | ≈ 600 | ≈ 2 | ? | 2001 | M. Brown, C. Trujillo, D. Rabinowitz | ||||
| 39.5 | 36.0 | 15.4 | ≈ 240–670 | ? | ? | ? | 2014 | Pan-STARRS | |||
| 39.5 | 36.7 | 19.4 | ≈ 240–670 | ? | ? | ? | 2014 | Pan-STARRS | |||
| 38628 Huya | 39.4 | 28.5 | 15.5 | ≈ 0.5 | 2000 | Ignacio Ferrin | |||||
| 39.3 | 27.4 | 12.0 | ≈ 0.012 | 2006 | Marc W. Buie | ||||||
| 39.3 | 34.5 | 13.3 | ≈ 1.7 | 2001 | M.W.Buie | ||||||
| 39.3 | 34.9 | 22.4 | ≈ 0.7 | 2001 | Marc W. Buie | ||||||
| 47171 Lempo | 39.3 | 30.6 | 8.4 | | 1999 | E. P. Rubenstein, L.-G. Strolger | |||||
| 39.3 | 31.2 | 14.0 | ≈ 0.16 | 2002 | Marc W. Buie | ||||||
| 39.3 | 28.9 | 14.0 | ≈ 1 | 2002 | NEAT | ||||||
| 39.4 | 30.4 | 16.3 | ≈ 0.15 | 2002 | NEAT |