astronomy Astronomy is a natural science that studies celestial objects and the phenomena that occur in the cosmos. It uses mathematics, physics, and chemistry in order to explain their origin and their overall evolution. Objects of interest includ ...

, the plutinos are a dynamical group of trans-Neptunian objects that orbit in 2:3

mean-motion resonance In celestial mechanics, orbital resonance occurs when orbiting bodies exert regular, periodic gravitational influence on each other, usually because their orbital periods are related by a ratio of small integers. Most commonly, this relation ...

with

Neptune Neptune is the eighth and farthest known planet from the Sun. It is the List of Solar System objects by size, fourth-largest planet in the Solar System by diameter, the third-most-massive planet, and the densest giant planet. It is 17 t ...

. This means that for every two orbits a plutino makes, Neptune orbits three times. The dwarf planet

Pluto Pluto (minor-planet designation: 134340 Pluto) is a dwarf planet in the Kuiper belt, a ring of Trans-Neptunian object, bodies beyond the orbit of Neptune. It is the ninth-largest and tenth-most-massive known object to directly orbit the Su ...

is the largest member as well as the namesake of this group. The next largest members are , , and . Plutinos are named after mythological creatures associated with the underworld. Plutinos form the inner part of the

Kuiper belt The Kuiper belt ( ) is a circumstellar disc in the outer Solar System, extending from the orbit of Neptune at 30 astronomical units (AU) to approximately 50 AU from the Sun. It is similar to the asteroid belt, but is far larger—20 times ...

and represent about a quarter of the known Kuiper belt objects. They are also the most populous known class of resonant trans-Neptunian objects ''(also see adjunct box with hierarchical listing)''. The first plutino after Pluto itself, (385185) 1993 RO, was discovered on September 16, 1993.

Orbits

Origin

It is thought that the objects that are currently in mean

orbital resonance In celestial mechanics, orbital resonance occurs when orbiting bodies exert regular, periodic gravitational influence on each other, usually because their orbital periods are related by a ratio of small integers. Most commonly, this relation ...

s with Neptune initially followed a variety of 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 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 A classical Kuiper belt object, also called a cubewano ( "QB1-o"), is a low-eccentricity Kuiper belt object (KBO) that orbits beyond Neptune and is not controlled by an orbital resonance with Neptune. Cubewanos have orbits with semi-major axe ...

family, while bodies with higher eccentricities (0.05 to 0.34) and semimajor axes close to the 3:2 Neptune resonance are primarily plutinos.

Orbital characteristics

While the majority of plutinos have relatively low

orbital inclination Orbital inclination measures the tilt of an object's orbit around a celestial body. It is expressed as the angle between a reference plane and the orbital plane or axis of direction of the orbiting object. For a satellite orbiting the Earth ...

s, 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

's outer edge (where objects in a 1:2 resonance with Neptune, the Twotinos, are found). 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: * , which follows the most highly inclined orbit (34.5°) *, which has the most elliptical orbit (its eccentricity is 0.33), with the perihelion halfway between Uranus and Neptune * following a quasi-circular orbit * lying almost perfectly on the

ecliptic The ecliptic or ecliptic plane is the orbital plane of Earth's orbit, Earth around the Sun. It was a central concept in a number of ancient sciences, providing the framework for key measurements in astronomy, astrology and calendar-making. Fr ...

(inclination less than 1.5°) * 15810 Arawn, a quasi-satellite of Pluto See also the comparison with the distribution of the cubewanos.

Long-term stability

Pluto's influence on the other plutinos has historically been neglected due to its relatively 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 The Hill sphere is a common model for the calculation of a Sphere of influence (astrodynamics), gravitational sphere of influence. It is the most commonly used model to calculate the spatial extent of gravitational influence of an astronomical ...

(gravitational influence). 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

File:OrcusandPlutoRotatingFrame.gif, The motions of Orcus and

in a

rotating frame A rotating frame of reference is a special case of a non-inertial reference frame that is rotation, rotating relative to an inertial reference frame. An everyday example of a rotating reference frame is the surface of the Earth. (This article co ...

with a period equal to

orbital period The orbital period (also revolution period) is the amount of time a given astronomical object takes to complete one orbit around another object. In astronomy, it usually applies to planets or asteroids orbiting the Sun, moons orbiting planets ...

(holding Neptune stationary). Pluto is grey, Orcus is red, and Neptune is the white (stationary) dot at 5 o'clock. Uranus is blue, Saturn yellow, and Jupiter red. File:TheKuiperBelt 60AU LargePlutinos.svg, Orbits and sizes of the larger plutinos (and the reference non-plutino ). Orbital

eccentricity Eccentricity or eccentric may refer to: * Eccentricity (behavior), odd behavior on the part of a person, as opposed to being "normal" Mathematics, science and technology Mathematics * Off-Centre (geometry), center, in geometry * Eccentricity (g ...

is represented by segments extending horizontally from

perihelion An apsis (; ) is the farthest or nearest point in the orbit of a planetary body about its primary body. The line of apsides (also called apse line, or major axis of the orbit) is the line connecting the two extreme values. Apsides perta ...

aphelion An apsis (; ) is the farthest or nearest point in the orbit of a planetary body about its primary body. The line of apsides (also called apse line, or major axis of the orbit) is the line connecting the two extreme values. Apsides perta ...

;

inclination Orbital inclination measures the tilt of an object's orbit around a celestial body. It is expressed as the angle between a reference plane and the orbital plane or axis of direction of the orbiting object. For a satellite orbiting the Eart ...

is shown on the vertical axis. File:TheKuiperBelt 60AU Plutinos distribution.svg, The distribution of plutinos (and the reference non-plutino ). Small inserts show

histogram A histogram is a visual representation of the frequency distribution, distribution of quantitative data. To construct a histogram, the first step is to Data binning, "bin" (or "bucket") the range of values— divide the entire range of values in ...

s for the distributions of orbital inclination and eccentricity.

Brightest objects

The plutinos brighter than H_V=6 include: (link to all of the orbits of these objects listed above ar
here

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., (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

was used for orbit classification.

External links

{{Trans-Neptunian objects Solar System