planetary science Planetary science (or more rarely, planetology) is the scientific study of planets (including Earth), celestial bodies (such as moons, asteroids, comets) and planetary systems (in particular those of the Solar System) and the processes of their f ...

, the term unusual minor planet, or ''unusual object'', is used for a

minor planet According to the International Astronomical Union (IAU), a minor planet is an astronomical object in direct orbit around the Sun that is exclusively classified as neither a planet nor a comet. Before 2006, the IAU officially used the term ''minor ...

that possesses an unusual physical or orbital characteristic. For the

Minor Planet Center The Minor Planet Center (MPC) is the official body for observing and reporting on minor planets under the auspices of the International Astronomical Union (IAU). Founded in 1947, it operates at the Smithsonian Astrophysical Observatory. Function ...

(MPC), which operates under the auspices of the

International Astronomical Union The International Astronomical Union (IAU; french: link=yes, Union astronomique internationale, UAI) is a nongovernmental organisation with the objective of advancing astronomy in all aspects, including promoting astronomical research, outreac ...

, any non-classical

main-belt asteroid The asteroid belt is a torus-shaped region in the Solar System, located roughly between the orbits of the planets Jupiter and Mars. It contains a great many solid, irregularly shaped bodies, of many sizes, but much smaller than planets, called ...

, which account for the vast majority of all minor planets, is an unusual minor planet. These include the

near-Earth object A near-Earth object (NEO) is any small Solar System body whose orbit brings it into proximity with Earth. By convention, a Solar System body is a NEO if its closest approach to the Sun (perihelion) is less than 1.3 astronomical units (AU). ...

s and

Trojans Trojan or Trojans may refer to: * Of or from the ancient city of Troy * Trojan language, the language of the historical Trojans Arts and entertainment Music * ''Les Troyens'' ('The Trojans'), an opera by Berlioz, premiered part 1863, part 1890 ...

as well as the

distant minor planet A distant minor planet, or ''distant object'', is any minor planet found beyond Jupiter in the outer Solar System that is not commonly thought of as an "asteroid". The umbrella term is used by IAU's Minor Planet Center (MPC), which is responsibl ...

s such as

centaurs A centaur ( ; grc, κένταυρος, kéntauros; ), or occasionally hippocentaur, is a creature from Greek mythology with the upper body of a human and the lower body and legs of a horse. Centaurs are thought of in many Greek myths as being ...

and

trans-Neptunian object A trans-Neptunian object (TNO), also written transneptunian object, is any minor planet in the Solar System that orbits the Sun at a greater average distance than Neptune, which has a semi-major axis of 30.1 astronomical units (au). Typically, ...

s. In a narrower sense, the term is used for a group of bodies – including

Mars-crosser A Mars-crossing asteroid (MCA, also Mars-crosser, MC) is an asteroid whose orbit crosses that of Mars. Some Mars-crossers numbered below 100000 are listed here. They include the two numbered Mars trojans 5261 Eureka and . Many databases, for i ...

s, centaurs and otherwise non-classifiable minor planets – that show a high

orbital eccentricity In astrodynamics, the orbital eccentricity of an astronomical object is a dimensionless parameter that determines the amount by which its orbit around another body deviates from a perfect circle. A value of 0 is a circular orbit, values betwee ...

, typically above 0.5 and/or a

perihelion An apsis (; ) is the farthest or nearest point in the orbit of a planetary body about its primary body. For example, the apsides of the Earth are called the aphelion and perihelion. General description There are two apsides in any ellip ...

of less than 6 AU. Similarly, an unusual asteroid (UA) is an

inner Solar System The Solar SystemCapitalization of the name varies. The International Astronomical Union, the authoritative body regarding astronomical nomenclature, specifies capitalizing the names of all individual astronomical objects but uses mixed "Solar S ...

object with a high eccentricity and/or

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

but with a perihelion larger than 1.3 AU, which does exclude the

Other unusual objects

According to the MPC, other unusual minor planets are objects, which orbital characteristics do not fit those of the near-Earth and distant populations. These objects typically have high eccentricities, and inclinations often more than 90 degrees (retrograde orbits), a criterion that is common among the members of the

damocloid Damocloids are a class of minor planets such as 5335 Damocles and 1996 PW that have Halley-type or long-period highly eccentric orbits typical of periodic comets such as Halley's Comet, but without showing a cometary coma or tail. ...

population. Object in this list have a T_Jupiter of less than 3 and a

between 1.67 and 5.5 AU, that is, they do not cross the orbit of Mars but cross or at least come close to Jupiter's orbit at 5.2 AU. According to the SSBN07 classification, such objects have cometary dynamics. , the list contains 211 objects, most of which remain unnumbered. A bold designation links to an object's stand-alone article.

Characteristics

Extinct comet An extinct comet is a comet that has expelled most of its volatile ice and has little left to form a tail and coma. In a dormant comet, rather than being depleted, any remaining volatile components have been sealed beneath an inactive surface la ...

, are considered unusual minor planets in having the orbital characteristics of a

long period Long may refer to: Measurement * Long, characteristic of something of great duration * Long, characteristic of something of great length * Longitude (abbreviation: long.), a geographic coordinate * Longa (music), note value in early music mensur ...

, Jupiter-family or

Halley-type comet A comet is an icy, small Solar System body that, when passing close to the Sun, warms and begins to release gases, a process that is called outgassing. This produces a visible atmosphere or coma, and sometimes also a tail. These phenomena are ...

but showing no sign of cometary activity. *

Damocloid Damocloids are a class of minor planets such as 5335 Damocles and 1996 PW that have Halley-type or long-period highly eccentric orbits typical of periodic comets such as Halley's Comet, but without showing a cometary coma or tail. ...

, with typically highly inclined orbits, often being retrograde.

Examples

1996 PW is an exceptionally eccentric trans-Neptunian object and damocloid on an orbit typical of long-period comets but one that showed no sign of cometary activity around the time it was discovered. The Unusual minor planet, unusual object measures app ...

(TNO, LPC) * 1998 WU24 (CEN, HTC) * (33342) 1998 WT24 (NEO) * 2011 YU75 (CEN)

References

{{Reflist, refs= {{cite web , title = Unusual Minor Planets , work = Minor Planet Center , url = https://www.minorplanetcenter.net/iau/Unusual.html , access-date = 14 November 2018 {{cite web , title = List Of Other Unusual Objects , work = Minor Planet Center , url = https://www.minorplanetcenter.net/iau/lists/t_others.html , access-date= 19 August 2021 {{Cite journal , display-authors = 6 , first1 = John K. , last1 = Davies , first2 = David J. , last2 = Tholen , first3 = Robert J. , last3 = Whiteley , first4 = Simon F. , last4 = Green , first5 = Jon K. , last5 = Hillier , first6 = Michael J. , last6 = Foster , first7 = Neil , last7 = McBride , first8 = Tom. H. , last8 = Kerr , first9 = Erica , last9 = Muzzerall , date = March 2001 , title = The Lightcurve and Colors of Unusual Minor Planet 1998 WU 24 , journal = Icarus , volume = 150 , issue = 1 , pages = 69–77 , bibcode = 2001Icar..150...69D , doi = 10.1006/icar.2000.6554 {{Cite journal , first1 = Yanga R. , last1 = Fernández , first2 = David C. , last2 = Jewitt , first3 = Scott S. , last3 = Sheppard , date = July 2005 , title = Albedos of Asteroids in Comet-Like Orbits , journal = The Astronomical Journal , volume = 130 , issue = 1 , pages = 308–318 , bibcode = 2005AJ....130..308F , doi = 10.1086/430802 , citeseerx = 10.1.1.507.2206 {{cite journal , last1 = Gladman , first1 = B. , last2 = Marsden , first2 = B. G. , last3 = Vanlaerhoven , first3 = C. , title = Nomenclature in the Outer Solar System , journal = The Solar System Beyond Neptune , page = 43 , date = 2008 , url = https://www.lpi.usra.edu/books/ssbn2008/7002.pdf , bibcode = 2008ssbn.book...43G}

External links

MPC data page

1996 PW, JPL, August 1996
The lightcurve and colors of unusual minor planet 1996 PW

(remanzacco)

(remanzacco)

Other unusual objects

Characteristics

Examples

See also

References

External links