Provisional designation in astronomy
Provisional designation in astronomy is the naming convention
Astronomical naming conventions
In ancient times, only the Sun and Moon, a few hundred stars and the most easily visible planets had names. Over the last few hundred years, the number of identified astronomical objects has risen from hundreds to over a billion, and more are discovered every year...

 applied to astronomical object
Astronomical object
Astronomical objects or celestial objects are naturally occurring physical entities, associations or structures that current science has demonstrated to exist in the observable universe. The term astronomical object is sometimes used interchangeably with astronomical body...

s 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 The provisional designation is usually superseded by a permanent designation once a reliable orbit has been calculated.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 asteroids, so many have been discovered that many will never be named by their discoverers.

Minor planets

The current system of provisional designation of minor planet
Minor planet
An asteroid group or minor-planet group is a population of minor planets that have a share broadly similar orbits. Members are generally unrelated to each other, unlike in an asteroid family, which often results from the break-up of a single asteroid...

s (asteroid
Asteroids are a class of small Solar System bodies in orbit around the Sun. They have also been called planetoids, especially the larger ones...

s, centaurs and trans-Neptunian object
Trans-Neptunian object
A trans-Neptunian object is any minor planet in the Solar System that orbits the Sun at a greater distance on average than Neptune.The first trans-Neptunian object to be discovered was Pluto in 1930...

s) has been in place since 1925, and superseded several previous conventions, each of which was rendered obsolete by the increasing numbers of asteroid discoveries.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 the 15th of the month, regardless of the numbers of days in the second "half".

The second letter and the number indicate the order or 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 since 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 asteroid discovered in the second half of March 1950 would be . For technical reasons, such as ASCII
The American Standard Code for Information Interchange is a character-encoding scheme based on the ordering of the English alphabet. ASCII codes represent text in computers, communications equipment, and other devices that use text...

 limitations, the subscript is sometimes "flattened out", so that this could be written 1950 FC1. The subscripts were first used with .

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.

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


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 . The next discovery is , then , etc. Eventually one could get to something like . 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
Trans-Neptunian object
A trans-Neptunian object is any minor planet in the Solar System that orbits the Sun at a greater distance on average than Neptune.The first trans-Neptunian object to be discovered was Pluto in 1930...

 90377 Sedna
90377 Sedna
90377 Sedna is a trans-Neptunian object discovered in 2003, which was about three times as far from the Sun as Neptune. For most of its orbit it is even further from the Sun, with its aphelion estimated at 960 astronomical units , making it one of the most distant known objects in the Solar System...

 had the provisional designation , 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
28978 Ixion
28978 Ixion is a Kuiper belt object discovered on May 22, 2001. Ixion is a plutino and a very likely dwarf planet; its diameter of 650 km estimated by Spitzer makes it about the fifth largest plutino. It is named after Ixion, a figure from Greek mythology...

, originally , was discovered in the latter half of May 2001, and was the (X->23 + 76*25 = 1923) 1,923rd object discovered during that time.

In practice, the numerical suffix is not always subscripted. For example, the provisional designation of 7934 Sinatra
7934 Sinatra
7934 Sinatra is a main-belt asteroid discovered on September 26, 1989 by E. W. Elst at the European Southern Observatory.- External links :*...

 can be expressed as either "" or "1989 SG1" (that is, 1989 is the discovery year, "S" is the eighteenth half-month of the year, and "G1" or "" indicates this was the thirty-third discovery during that half-month).

As of May 18, 2010, the busiest half-month has been the second half of October 2005. During those 16 days, 13,268 minor planets were observed and provisionally discovered, and the last one was named . As observations made then are further analyzed, that number may continue to climb.

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 asteroid in the Palomar-Leiden Survey is 2040 P-L
(185643) 2040 P-L
2040 P-L is a Mars-crossing minor planet. It was discovered by Cornelis Johannes van Houten, Ingrid van Houten-Groeneveld, and Tom Gehrels at the Palomar Observatory in San Diego County, California, on September 24, 1960.-External links:*...

. The majority of these bodies have since been assigned a number.

Historical designations

The first four asteroid
Asteroids are a class of small Solar System bodies in orbit around the Sun. They have also been called planetoids, especially the larger ones...

s 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 asteroids, 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
2 Pallas
Pallas, formally designated 2 Pallas, is the second asteroid to have been discovered , and one of the largest. It is estimated to constitute 7% of the mass of the asteroid belt, and its diameter of 530–565 km is comparable to, or slightly larger than, that of 4 Vesta. It is however 20%...

 a lozenge with a crossed handle (⚴) 3 Juno
3 Juno
Juno , formal designation 3 Juno in the Minor Planet Center catalogue system, was the third asteroid to be discovered and is one of the larger main-belt asteroids, being one of the two largest stony asteroids, along with 15 Eunomia. Juno is estimated to contain 1% of the total mass of the asteroid...

 a Venus mirror crowned by a star and 4 Vesta
4 Vesta
Vesta, formally designated 4 Vesta, is one of the largest asteroids, with a mean diameter of about . It was discovered by Heinrich Wilhelm Olbers on March 29, 1807, and is named after the Roman virgin goddess of home and hearth, Vesta....

 a sacred fire altar (

It soon became apparent, though, that continuing to assign symbols was impractical and provided no assistance when the number of known asteroids was in the tens. Johann Franz Encke
Johann Franz Encke
Johann Franz Encke was a German astronomer. Among his activities, he worked on the calculation of the periods of comets and asteroids, measured the distance from the earth to the sun, and made observations on the planet Saturn.-Biography:Encke was born in Hamburg, where his father was a...

 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 asteroids received symbols, including 28 Bellona
28 Bellona
28 Bellona is a large main-belt asteroid.Bellona was discovered by R. Luther on March 1, 1854. It is named after Bellona, the Roman goddess of war; the name was chosen to mark the beginning of the Crimean War.-External links:...

 the whip and lance of Mars' martial sister, 35 Leukothea
35 Leukothea
35 Leukothea is a large, dark main-belt asteroid.It was discovered by R. Luther on April 19, 1855, and named after Leukothea, a sea goddess in Greek mythology.-References:...

 an ancient lighthouse and 37 Fides
37 Fides
37 Fides is a large main-belt asteroid.It was discovered by R. Luther on October 5, 1855, and named after Fides, the Roman goddess of loyalty.-References:...

 a Latin cross (
). According to Webster's A Dictionary of the English Language, four more asteroids were also given symbols: 16 Psyche
16 Psyche
16 Psyche )is one of the ten most massive main-belt asteroids. It is over 200 kilometers in diameter and contains a little less than 1% of the mass of the entire asteroid belt. It is the most massive of the metallic M-type asteroids....

, 17 Thetis
17 Thetis
17 Thetis is a large main-belt asteroid. It is an S-type asteroid, therefore giving it a relatively bright silicate surface.It was discovered by R. Luther on April 17, 1852. It was his first asteroid discovery. Its name comes from Thetis, the mother of Achilles in Greek mythology.One Thetidian...

, 26 Proserpina
26 Proserpina
26 Proserpina is a main-belt asteroid.It was discovered by R. Luther on May 5, 1853.It is named after the Roman goddess Proserpina, the daughter of Ceres and the Queen of the Underworld.-References:...

, and 29 Amphitrite
29 Amphitrite
29 Amphitrite is one of the largest S-type asteroids, probably third in diameter after Eunomia and Juno, although Iris and Herculina are similar in size.-Discovery:...

. 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
Astronomische Nachrichten
Astronomische Nachrichten , one of the first international journals in the field of astronomy, was founded in 1821 by the German astronomer Heinrich Christian Schumacher. It claims to be the oldest astronomical journal in the world that is still being published...

(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
333 Badenia
333 Badenia is a large C-type asteroid in the outer asteroid belt.It was discovered by Max Wolf on August 22, 1892 in Heidelberg.-References:###...

 was initially designated 1892 A, 163 Erigone
163 Erigone
163 Erigone is a dark-coloured, fairly big Main belt asteroid, the namesake of the Erigone family of asteroids. It was discovered by J. Perrotin on April 26, 1876 and named after one of the two Erigones in Greek mythology....

 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
379 Huenna
379 Huenna is a large Themistian asteroid. It is classified as a C-type asteroid and is probably composed of carbonaceous material.It was discovered by Auguste Charlois on January 8, 1894 in Nice...

 followed 1893 AP
378 Holmia
378 Holmia is a typical Main belt asteroid.It was discovered by Auguste Charlois on December 6, 1893 in Nice....

 and so on. In 1916, the letters reached ZZ
830 Petropolitana
-External links:*...

 and, rather than starting a series of triple-letter designations, the double-letter series was restarted with 1916 AA
831 Stateira
-External links:*...


Since a considerable amount of time could sometimes elapse between exposing the photographic plates of an astronomical survey and actually spotting an asteroid on them (witness the story of Phoebe
Phoebe (moon)
Phoebe is an irregular satellite of Saturn. It was discovered by William Henry Pickering on 17 March 1899 from photographic plates that had been taken starting on 16 August 1898 at the Boyden Observatory near Arequipa, Peru, by DeLisle Stewart...

'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 he was 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
6484 Barthibbs
6484 Barthibbs is a main-belt asteroid discovered on March 23, 1990 by Helin, E. F. at Palomar.- External links :*...

 (note that there is a space between the year and the letter to distinguish this designation from the old-style comet designation 1915a), 1917 b
886 Washingtonia
-External links:*...

. 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 III 1/2". 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
4P/Faye is a periodic comet discovered in November, 1843, by Hervé Faye at the Royal Observatory in Paris....

) 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 asteroids. For comets, the provisional designation consists of the year of discovery, a space, ONE letter (unlike the asteroids 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, asteroid 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 was reclassified as a comet, and because it was discovered by LINEAR
In mathematics, a linear map or function f is a function which satisfies the following two properties:* Additivity : f = f + f...

, 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
Comet Ikeya-Zhang is a comet discovered independently by two astronomers from Japan and China in 2002....

, 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
X/1106 C1
X/1106 C1, also known as the Great Comet of 1106, was a Great Comet that appeared on February 2, 1106, and was observed across the world from the beginning of February through to mid-March. It was recorded by astronomers in Wales, England, Japan, Korea, China and Europe. It was observed to split...


Provisional designations for comets are given condensed or "packed form" in the same manner as asteroids. 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 asteroid designations not to overlap.

Satellites and rings of planets

When satellites or rings
Planetary ring
A planetary ring is a ring of cosmic dust and other small particles orbiting around a planet in a flat disc-shaped region.The most notable planetary rings known in Earth's solar system are those around Saturn, but the other three gas giants of the solar system possess ring systems of their...

 are first discovered, they are given provisional designations such as "" (the 11th new satellite of Jupiter
Jupiter is the fifth planet from the Sun and the largest planet within the Solar System. It is a gas giant with mass one-thousandth that of the Sun but is two and a half times the mass of all the other planets in our Solar System combined. Jupiter is classified as a gas giant along with Saturn,...

 discovered in 2000), "" (the first new satellite of Pluto
Pluto, formal designation 134340 Pluto, is the second-most-massive known dwarf planet in the Solar System and the tenth-most-massive body observed directly orbiting the Sun...

 discovered in 2005), or "" (the second new ring of Saturn
Saturn is the sixth planet from the Sun and the second largest planet in the Solar System, after Jupiter. Saturn is named after the Roman god Saturn, equated to the Greek Cronus , the Babylonian Ninurta and the Hindu Shani. Saturn's astronomical symbol represents the Roman god's sickle.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 comet
A comet is an icy small Solar System body that, when close enough to the Sun, displays a visible coma and sometimes also a tail. These phenomena are both due to the effects of solar radiation and the solar wind upon the nucleus of the comet...

s. These designations are sometimes written as "", 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
Naiad (moon)
Naiad , also known as Neptune III, is the innermost satellite of Neptune, named after the Naiads of Greek legend.Naiad was discovered sometime before mid-September 1989 from the images taken by the Voyager 2 probe. The last moon to be discovered during the flyby, it was designated...

, the innermost moon of Neptune, was at first designated "". Later, once its existence and orbit were confirmed, it received its full designation, "".

The Roman numbering system arose with the very first discovery of natural satellites other than Earth's Moon: Galileo referred to the Galilean moons
Galilean moons
The Galilean moons are the four moons of Jupiter discovered by Galileo Galilei in January 1610. They are the largest of the many moons of Jupiter and derive their names from the lovers of Zeus: Io, Europa, Ganymede and Callisto. Ganymede, Europa and Io participate in a 1:2:4 orbital resonance...

 as I through IV (counting from Jupiter outward), in part to spite his rival Simon Marius
Simon Marius
Simon Marius was a German astronomer. He was born in Gunzenhausen, near Nuremberg, but he spent most of his life in the city of Ansbach....

, 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. "" is Amalthea
Amalthea (moon)
Amalthea is the third moon of Jupiter in order of distance from the planet. It was discovered on September 9, 1892, by Edward Emerson Barnard and named after Amalthea, a nymph in Greek mythology. It is also known as '....

, which orbits closer to Jupiter than does Io
Io (moon)
Io ) is the innermost of the four Galilean moons of the planet Jupiter and, with a diameter of , the fourth-largest moon in the Solar System. It was named after the mythological character of Io, a priestess of Hera who became one of the lovers of Zeus....

). 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
Timeline of discovery of solar system planets and their natural satellites
The timeline of discovery of Solar System planets and their natural satellites charts the progress of the discovery of new bodies over history...

). The convention has been extended to natural satellites of minor planets, such as "".

Moons of minor planets

The provisional designation system for minor planet satellites, such as asteroid moon
Asteroid moon
A minor planet moon is an astronomical body that orbits a minor planet as its natural satellite. It is thought that many asteroids and Kuiper belt objects may possess moons, in some cases quite substantial in size...

s, 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
87 Sylvia
87 Sylvia is one of the largest main-belt asteroids. It is a member of the Cybele group located beyond the core of the belt . Sylvia is remarkable for being the first asteroid known to possess more than one moon....

, 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.

External links

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