Minor planet designation

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For the provisional designation of minor planets, see Provisional designation in astronomy.

Formal minor planet designations are number–name combinations overseen by the Minor Planet Center, a branch of the IAU. They are used for dwarf planets and small Solar System bodies such as asteroids, but not comets. They are assigned to a body once its orbit is secured, and are unrelated to provisional designations, which are automatically assigned when an object is discovered.

A formal designation consists of two parts: a catalog number, historically assigned in approximate order of discovery, and either a name, typically assigned by the discoverer, or, the minor planet's provisional designation (see details in § Syntax).:[1]

Nowadays a number is assigned only after the orbit has been secured by 4 well-observed oppositions.[2] For unusual objects, such as near-Earth asteroids (NEAs), numbering might already occur after three, maybe even only two, oppositions.[2] Among the nearly half a million minor planets that received a number,[3] only about 20 thousand (or 4%) have received a name. In addition, more than 200,000 minor planets have not even been numbered.[3]

The convention for satellites of minor planets, such as the formal designation (87) Sylvia I Romulus for the asteroid moon Romulus, is an extension of the Roman numeral convention that had been used, on and off, for the moons of the planets since Galileo's time. Comets are also managed by the Minor Planet Center, but use a different cataloguing system.


The permanent syntax is:

For example, the unnamed minor planet (388188) 2006 DP14 has its number always written in parentheses, while for named minor planets such as (274301) Wikipedia, the parentheses may be dropped as in 274301 Wikipedia. Parentheses are now often omitted in prominent databases such as the SDBD. (Note: on English Wikipedia, named minor planets never use parentheses in their designations. However, redirects form parenthetical versions exist for most lower-numbered and well-known objects.)

Since minor planet designations change over time, different versions may be used in astronomy journals. When the main-belt asteroid 274301 Wikipedia was discovered in August 2008, it was provisionally designated 2008 QH24, before it received a number and was then written as (274301) 2008 QH24. On 27 January 2013, it was named Wikipedia after being published in the Minor Planet Circulars.[4][5]

According to the preference of the astronomer and publishing date of the journal, 274301 Wikipedia, may be referred to as 2008 QH24, or simply as (274301). In practice, for any reasonably well-known object the number is mostly a catalogue entry, and the name or provisional designation is generally used in place of the formal designation. So Pluto is rarely written as 134340 Pluto, and 2002 TX300 is more commonly used than the longer version (55636) 2002 TX300.


By 1851 there were 15 known asteroids, all but one with their own symbol. The symbols grew increasingly complex as the number of objects grew, and, as they had to be drawn by hand, astronomers found some of them difficult. This difficulty was addressed by Benjamin Apthorp Gould in 1851, who suggested numbering asteroids in their order of discovery, and placing this number in a circle as the symbol for the asteroid, such as ④ for the fourth asteroid, Vesta. This practice was soon coupled with the name itself into an official number-name designation, "④ Vesta", as the number of minor planets increased. By the late 1850s, the circle had been simplified to parentheses, "(4)" and "(4) Vesta", which was easier to typeset. Other punctuation such as "4) Vesta" and "4, Vesta" was also used, but had more or less completely died out by 1949.[6]

The major exception to the convention that the number tracks the order of discovery or determination of orbit is the case of Pluto. Since Pluto was initially classified as a planet, it was not given a number until a 2006 redefinition of "planet" that excluded it. At that point, Pluto was given the formal designation (134340) Pluto.

See also[edit]


  1. ^ "How Minor Planet Are Named". IAU – International Astronomical Union. 2005. Archived from the original on 16 February 2006. Retrieved 5 January 2017. 
  2. ^ a b "How Are Minor Planets Named?". Minor Planet Center. Retrieved 2014-02-25. 
  3. ^ a b "How Many Solar System Bodies". Jet Propulsion Laboratory. Retrieved 5 January 2017. 
  4. ^ "274301 Wikipedia (2008 QH24)". Minor Planet Center. Retrieved 5 January 2017. 
  5. ^ "MPC/MPO/MPS Archive". Minor Planet Center. Retrieved 5 January 2017. 
  6. ^ From Dr. James Hilton's When Did the Asteroids Become Minor Planets?, particularly the discussion of Gould, B. A. 1852, On the Symbolic Notation of the Asteroids, Astronomical Journal, Vol. 2, and immediately subsequent history. The discussion of C. J. Cunningham (1988), also from there, explains the parenthetical part.

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