Provisional designation in astronomy

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Provisional designation in astronomy is the naming convention applied to astronomical objects immediately following their discovery. The provisional designation is usually superseded by a permanent designation once a reliable orbit has been calculated. In the case of minor planets, so many have been discovered that many will never be named by their discoverers.

Minor planets

The current system of provisional designation of minor planets (asteroids, centaurs and trans-Neptunian objects) has been in place since 1925, and superseded several previous conventions, each of which was rendered obsolete by the increasing numbers of minor planet discoveries.

The first element in a minor planet's provisional designation is the year of discovery, followed by two letters and, optionally, a number.

The first letter indicates the half-month of the object's discovery within that year —"A" denotes discovery in the first half of January, "D" is for the second half of February, "J" is for the first half of May ("I" is not used), and so on until "Y" for the second half of December. The first half is always the 1st through to the 15th of the month, regardless of the numbers of days in the second "half".

The second letter and the number indicate the order of discovery within that half-month. The 8th minor planet discovered in the second half of March 1950, for example, would be provisionally designated 1950 FH. But because modern techniques typically yield far more than 25 objects (again, "I" is not used) in a half-month, a subscript number is appended to indicate the number of times that the letters have cycled through. Thus, the 28th minor planet discovered in the second half of March 1950 would be 1950 FC1. For technical reasons, such as ASCII limitations, the subscript is sometimes "flattened out", so that this could be written 1950 FC1. The subscripts were first used with 1926 GA1.

An idiosyncrasy of this system is that the second letter is listed before the number, even though the second letter is considered "least-significant". This is in contrast to most of the world's numbering systems. This idiosyncrasy is not seen, however, in online and electronic documents, where the number is frequently written before the final letter in so-called "packed form". For example, in electronic communications regarding minor planets 1926 GA1 would usually be written 1926G01A.

First letter
Jan 1 Jan 16 Feb 1 Feb 16 Mar 1 Mar 16 Apr 1 Apr 16 May 1 May 16 Jun 1 Jun 16 Jul 1 Jul 16 Aug 1 Aug 16 Sep 1 Sep 16 Oct 1 Oct 16 Nov 1 Nov 16 Dec 1 Dec 16
Second letter
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25
none 1 2 3 4 5 6 7 8 9 10 11 12 ... n
0 25 50 75 100 125 150 175 200 225 250 275 300 25 * n

Further examples

In the year 2004, the first minor planet discovery of January 1 would be named 2004 AA. Then the naming continues to 2004 AZ, followed by 2004 AA1. The next discovery is 2004 AB1, then 2004 AC1, etc. Eventually one could get to something like 2004 AA276. Following the end of the half-month, the next body to be discovered would receive the provisional designation 2004 BA.

The large trans-Neptunian object 90377 Sedna had the provisional designation 2003 VB12, meaning it was discovered in the first half of November 2003, and that it was the 302nd object (B->2 + 12*25 = 302) discovered during that time. 28978 Ixion, originally 2001 KX76, was discovered in the latter half of May 2001, and was the (X->23 + 76*25 = 1923) 1,923rd object discovered during that time.

As mentioned earlier, in practice the numerical suffix is not always subscripted. For example, the provisional designation of 7934 Sinatra can be expressed as either "1989 SG1" or "1989 SG1" (that is, 1989 is the discovery year, "S" is the eighteenth half-month of the year, and "G1" or "G1" indicates this was the thirty-second discovery during that half-month).

As of March 20, 2012, the busiest half-month was the second half of October 2005.1 During those 16 days, 13,276 minor planets were observed and provisionally discovered, the last one being 2005 UA531 (a precovery of 2010 CC172);2 the highest-numbered main designation is 2005 UX530.3 As observations made then are further analyzed, that number may continue to climb slightly.

Survey designations

Minor planets discovered during four special past surveys have designations that consist of a number (order in the survey) followed by a space and one of the identifiers:

  • P-L Palomar-Leiden Survey (1960)
  • T-1 First Trojan Survey (1971)
  • T-2 Second Trojan Survey (1973)
  • T-3 Third Trojan Survey (1977)

For example, the 2040th minor planet in the Palomar-Leiden Survey is 2040 P-L. The majority of these bodies have since been assigned a number.

Historical designations

The first four minor planets were discovered in the early 19th century, after which there was a lengthy gap before the discovery of the fifth. Astronomers initially had no reason to believe that there would be countless thousands of minor planets, and strove to assign a symbol to each new discovery, in the tradition of the symbols used for the major planets. For example, 1 Ceres was assigned a stylized sickle (⚳) 2 Pallas a lozenge with a crossed handle (⚴) 3 Juno a Venus mirror crowned by a star (noframe, later became a star with a crossed handle, ⚵) and 4 Vesta a sacred fire altar (noframe).4

It soon became apparent, though, that continuing to assign symbols was impractical and provided no assistance when the number of known minor planets was in the tens. Johann Franz Encke introduced a new system in the Berliner Astronomisches Jahrbuch (BAJ) for 1854, published in 1851, in which he used encircled numbers instead of symbols. Encke's system began the numbering with Astrea which was given the number (1) and went through (11) Eunomia, while Ceres, Pallas, Juno and Vesta continued to be denoted by symbols, but in the following year's BAJ, the numbering was changed so that Astraea was number (5).

The new system found popularity among astronomers, and since then, the final designation of a minor planet is a number indicating its order of discovery followed by a name. Even after the adoption of this system, though, several more minor planets received symbols, including 28 Bellona the whip and lance of Mars' martial sister,5 35 Leukothea an ancient lighthouse6 and 37 Fides a Latin cross (noframe).7 According to Webster's A Dictionary of the English Language, four more minor planets were also given symbols: 16 Psyche, 17 Thetis, 26 Proserpina, and 29 Amphitrite.8 However, there is no evidence that these symbols were ever used outside of their initial publication in the Astronomische Nachrichten.

Genesis of the current system

Several different notation and symbolic schemes were used during the latter half of the nineteenth century, but the present form first appeared in the journal Astronomische Nachrichten (AN) in 1892. New numbers were assigned by the AN on receipt of a discovery announcement, and a permanent designation was then assigned once an orbit had been calculated for the new object.

At first, the provisional designation consisted of the year of discovery followed by a letter indicating the sequence of the discovery, but omitting the letter I (historically, sometimes J was omitted instead). Under this scheme, 333 Badenia was initially designated 1892 A, 163 Erigone was 1892 B, etc. In 1893, though, increasing numbers of discoveries forced the revision of the system to use double letters instead, in the sequence AA, AB...AZ, BA and so on. The sequence of double letters was not restarted each year, so that 1894 AQ followed 1893 AP and so on. In 1916, the letters reached ZZ and, rather than starting a series of triple-letter designations, the double-letter series was restarted with 1916 AA.

Because a considerable amount of time could sometimes elapse between exposing the photographic plates of an astronomical survey and actually spotting a small Solar System object on them (witness the story of Phoebe's discovery), or even between the actual discovery and the delivery of the message (from some far-flung observatory) to the central authority, it became necessary to retrofit discoveries into the sequence — to this day, discoveries are still dated based on when the images were taken, and not on when a human realised they were looking at something new. In the double-letter scheme, this was not generally possible once designations had been assigned in a subsequent year. The scheme used to get round this problem was rather clumsy and used a designation consisting of the year and a lower-case letter in a manner similar to the old provisional-designation scheme for comets. For example, 1915 a (note that there is a space between the year and the letter to distinguish this designation from the old-style comet designation 1915a, Mellish's first comet of 1915), 1917 b. In 1914 designations of the form year plus Greek letter were used in addition.


The system used previous to 1995 was complex. The year was followed by a space and then a Roman numeral (indicating the sequence of discovery) in most cases, but difficulties always arose when an object needed to be placed between previous discoveries. For example, after Comet 1881 III and Comet 1881 IV might be reported, an object discovered in between the discovery dates but reported much later couldn't be designated "Comet 1881 III½". More commonly comets were known by the discoverer's name and the year. An alternate scheme also listed comets in order of time of perihelion passage, using lower-case letters; thus "Comet Faye" (modern designation 4P/Faye) was both Comet 1881 I (first comet discovered in 1881) and Comet 1880c (third comet to pass at its perihelion in 1880 —note how the comet was discovered on its way out of our vicinity).

The system since 1995 is similar to the provisional designation of minor planets.9 For comets, the provisional designation consists of the year of discovery, a space, ONE letter (unlike the minor planets with two) indicating the half-month of discovery within that year (A=first half of January, B=second half of January, etc. skipping I and not reaching Z), and finally a number (not subscripted as with minor planets), indicating the sequence of discovery. Thus, the eighth comet discovered in the second half of March 2006 would be given the provisional designation 2006 F8, whilst the tenth comet of late March would be 2006 F10.

If a comet splits, its segments are given the same provisional designation with a suffixed letter A, B, C, ..., Z, a, b, c..., z. One presumes that tracking beyond 52 fragments is unlikely.

If an object is originally found asteroidal, and later develops a cometary tail, it retains its asteroidal designation. For example, minor planet 1954 PC turned out to be Comet Faye, and we thus have "4P/1954 PC" as one of the designations of said comet. Similarly, minor planet 1999 RE70 was reclassified as a comet, and because it was discovered by LINEAR, it is now known as 176P/LINEAR (LINEAR 52) and (118401) LINEAR.

Comets are assigned one of four possible prefixes as a rough classification. The prefix "P" (as in, for example, P/1997 C1, a.k.a. Comet Gehrels 4) designates a periodic comet, one which has an orbital period of less than 200 years or which has been observed during more than a single perihelion passage (e.g. 153P/Ikeya-Zhang, whose period is 367 years). They receive a permanent number prefix after their second observed perihelion passage (as of January 2007, there are 183 such comets).

Comets which do not fulfill the "periodic" requirements receive the "C" prefix (e.g. C/2006 P1, the Great Comet of 2007), but it should be noted that such comets may switch to "P" if they later fulfill the requirements. Comets which have been lost or have disintegrated are prefixed "D" (e.g. D/1993 F2, Comet Shoemaker-Levy 9). Finally, comets known from historical records but for which no reliable orbit could be calculated are prefixed "X" (e.g. X/1106 C1).

Provisional designations for comets are given condensed or "packed form" in the same manner as minor planets. 2006 F8, if a periodic comet, would be listed in the IAU Minor Planet Database as PK06F080. The last character is purposely a zero, as that allows comet and minor planet designations not to overlap.

Satellites and rings of planets

When satellites or rings are first discovered, they are given provisional designations such as "S/2000 J 11" (the 11th new satellite of Jupiter discovered in 2000), "S/2005 P 1" (the first new satellite of Pluto discovered in 2005), or "R/2004 S 2" (the second new ring of Saturn discovered in 2004). The initial "S/" or "R/" stands for "satellite" or "ring", respectively, distinguishing the designation from the prefixes "C/", "D/", "P/", and "X/" used for comets. These designations are sometimes written as "S/2005 P1", dropping the second space.

The prefix "S/" indicates a natural satellite, and is followed by a year (using the year when the discovery image was acquired, not necessarily the date of discovery). A one letter code identifies the planet (J, S, U, N, P for Jupiter, Saturn, Uranus, Neptune, and Pluto, respectively; see here for the full list), and then a number identifies sequentially the observation. For example, Naiad, the innermost moon of Neptune, was at first designated "S/1989 N 6". Later, once its existence and orbit were confirmed, it received its full designation, "Neptune III Naiad".

The Roman numbering system arose with the very first discovery of natural satellites other than Earth's Moon: Galileo referred to the Galilean moons as I through IV (counting from Jupiter outward), in part to spite his rival Simon Marius, who had proposed the names now adopted. Similar numbering schemes naturally arose with the discovery of moons around Saturn and Mars. Although the numbers initially designated the moons in orbital sequence, new discoveries soon failed to conform with this scheme (e.g. "Jupiter V" is Amalthea, which orbits closer to Jupiter than does Io). The unstated convention then became, at the close of the 19th century, that the numbers more or less reflected the order of discovery, except for prior historical exceptions (see the Timeline of discovery of Solar System planets and their natural satellites). The convention has been extended to natural satellites of minor planets, such as "(87) Sylvia I Romulus".

Moons of minor planets

The provisional designation system for minor planet satellites, such as asteroid moons, follows that established for the satellites of the major planets. With minor planets, the planet letter code is replaced by the minor planet number in parentheses. Thus, the first observed moon of 87 Sylvia, discovered in 2001, was at first designated S/2001 (87) 1, later receiving its permanent designation of (87) Sylvia I Romulus. Where more than one moon has been discovered, Roman numerals specify the discovery sequence, so that Sylvia's second moon is designated (87) Sylvia II Remus.

See also


External links

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