Provisional designation in astronomy

Yearly number of provisional minor planet designations assigned by the MPC since 1990. As of May 2019, a total of 1,426,477 designations have been assigned since 1869.[1]

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 The provisional designation is usually superseded by a permanent designation once a reliable orbit has been calculated.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 more than 900,000 minor planets,[2] approximately a third remains provisionally designated, as hundreds of thousands have been discovered in the last two decades.[3]

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designation of minor planets (asteroids, centaurs and trans-Neptunian objects) has been in place since 1925, and superseded several previous conventions, each of which was rendered obsolete by the increasing numbers of minor planet discoveries. A modern or new-style provisional designation consists of the year of discovery, followed by two letters and, optionally, a suffixed number.[4]

New-style provisional designation[]

For example, the provisional designation 2016 EK156 stands for the 3910th body identified during 1–15 March 2016:

First letter [4][5]
January February March April May June July August September October November December
1–15 16–31 1–15 16–29 1–15 16–31 1–15 16–30 1–15 16–31 1–15 16–30 1–15 16–31 1–15 16–31 1–15 16–30 1–15 16–31 1–15 16–30 1–15 16–31
Second letter
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 25n

Further explanations[]

Survey designations[]

Minor planets discovered during the Palomar–Leiden survey including three subsequent Trojan-campaigns, which altogether discovered more than 4,000 asteroids and Jupiter trojans between 1960 and 1977,[6] have custom designations that consist of a number (order in the survey) followed by a space and one of the following identifiers:[4][5]

For example, the asteroid 6344 P-L is the 6344th minor planet in the original Palomar–Leiden survey, while the asteroid 4835 T-1 was discovered during the first Trojan-campaign. The majority of these bodies have since been assigned a number and many are already named.

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 (3 Juno symbol alternate.svg, later became a star with a crossed handle, ⚵) and 4 Vesta a sacred fire altar (Simbolo di Vesta.svg).[7]

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,[8] 35 Leukothea an ancient lighthouse[9] and 37 Fides a Latin cross (37 Fides symbol.svg).[10] 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.[11] 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.[4]

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.

Temporary minor planet designations[]

Temporary designations are custom designation given by an observer or discovering observatory prior to the assignment of a provisional designation by the MPC.[12] These intricate designations were used prior to the Digital Age, when communication was slow or even impossible (e.g. during WWI). The listed temporary designations by observatory/observer use uppercase and lowercase letters (LETTER, letter), digits, numbers and years, as well Roman numerals (ROM) and Greek letters (greek).[12]

Observatory Temp. designation Examples
Algiers Obs. Alger LETTER Alger A, Alger CM
Alg LETTER Alg A, Alg CM
Alma-Ata Alma-Ata [Nr.] number Alma-Ata Nr. 1
year A number 1952 A1, A1
Arequipa Arequipa letter Arequipa a
Areq letter Areq a
Arequipa number Arequipa 17
Areq number Areq 17
Belgrade Obs. year letter [(Beograd)] 1956 x (Beograd), 1956 x
letter x
Lowell Obs.
A number A0, A7
Heidelberg Obs. Wolf [Nr.] number Wolf Nr. 18, Wolf 18
Wolf letter Wolf u
Wolf greek Wolf alpha
Heid number Heid 1, Heid 234
Johannesburg Obs. LETTER A, E
G number G 1, G 21
T number T 9, T 16
Kyoto-Kwasan number 1, 6
letter d
La Plata Obs. [La Plata] year ROM La Plata 1951 I, 1951 I
[La Plata] year LETTER La Plata 1950 G, 1950 G
Lick [Asteroid] LETTER Asteroid B, B
Mount Wilson Obs. [Asteroid] LETTER Asteroid A, A
Purple Mountain Obs.
P.O. number P.O. 32, P.O. 189
PO number PO 32, PO 189
Crimean Astrophysical Obs.
N number N1
K number K1, K3423
Simeiz Obs. [1942] SIGMA K number 1942 SIGMA K1, SIGMA K1
[1942] SIG K number 1942 SIG K1, SIG K1
sigma number sigma 1, sigma 229
Taunton Obs. Taunton digit Taunton 83
Tokyo-Mitaka Tokyo LETTER Tokyo B
Tokyo letter Tokyo b
Tokyo number Tokyo 20
Tokyo year LETTER Tokyo 1954 D
Turku Obs. T- number T-1, T-774
Uccle Obs. letter [(Uccle)] p (Uccle), p
letter number [(Uccle)] x2 (Uccle), x2
[ year] U number 1945 U 12, U 12
Washington year W digit 1917 W 15, 1923 W 21
Yerkes Obs. Y.O. number Y.O. 23
YO number YO 23


The system used for comets was complex previous to 1995. Originally, 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 to pass perihelion in 1881) and Comet 1880c (third comet to be discovered in 1880).

The system since 1995 is similar to the provisional designation of minor planets.[13] 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 (to avoid confusion with the number 1 or the numeral I) and not reaching Z), and finally a number (not subscripted as with minor planets), indicating the sequence of discovery within the half-month. 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.

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.

Periodic comets[]

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 (see List of periodic comets).

Non-periodic comets[]

Comets which do not fulfill the "periodic" requirements receive the "C" prefix (e.g. C/2006 P1, the Great Comet of 2007). Comets initially labeled as "non-periodic" may, however, 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 for which no reliable orbit could be calculated, but are known from historical records, are prefixed "X" as in, for example, X/1106 C1. (Also see List of non-periodic comets and List of hyperbolic comets.)

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 written in upper case identifies the planet such as J and S for Jupiter and Saturn, respectively (see list of one-letter abbreviations), 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.

Packed designation[]

Packed designations are used in online and electronic documents as well as databases.

Packed minor planet designation[]

The Orbit Database (MPCORB)[14] of the Minor Planet Center (MPC) uses the "packed form" to refer to all provisionally designated minor planets.[15] The idiosyncrasy found in the new-style provisional designations, no longer exists in this packed-notation system, as the second letter is now listed after the subscript number, or its equivalent 2-digit code. For an introduction on provisional minor planet designations in the "un-packed" form, see § New-style provisional designation.

Provisional packed designations[]

The system of packed provisional minor planet designations:[16]

Contrary to the new-style system, the letter "i" is used in the packed form both for the year and the numeric suffix.[16] The compacting system provides upper and lowercase letters to encode up to 619 "cycles". This means that 15,500 designations ( = 619×25 + 25) within a half-month can be packed, which is a few times more than the designations assigned monthly in recent years.[1]

  1. 1995 XA is written as J95X00A
  2. 1995 XL1 is written as J95X01L
  3. 2016 EK156 is written as K16EF6K
  4. 2007 TA418 is written as K07Tf8A
  1. The year 1995 is compacted to J95. As it has no subscript number, 00 is used as placeholder instead, and directly placed after the half-month letter "X".
  2. The year 1995 is compacted to J95. Subscript number "1" is padded to 01 to maintain the length of 7 characters, and placed after the first letter.
  3. The year 2016 is compacted to K16. The subscript number "156" exceeds 2 digits and is converted to F6, (see table below)
  4. The year 2007 is compacted to K07. The subscript number "418" exceeds 2 digits and is converted to f8, (see table below)
Conversion tables
Compacting first two digits of year[16]
I J K L ...
1800s 1900s 2000s 2100s ...
Compacting 3-digit subscript numbers[16]
100s 110s 120s 130s 140s 150s 160s 170s 180s 190s 200s 210s 220s 230s 240s 250s 260s 270s
280s 290s 300s 310s 320s 330s 340s 350s 360s 370s 380s 390s 400s 410s 420s 430s 440s 450s
460s 470s 480s 490s 500s 510s 520s 530s 540s 550s 560s 570s 580s 590s 600s 610s

Packed survey designations[]

Survey designations used during the Palomar–Leiden Survey (PLS) have a simpler packed form, as for example:[1]

Note that the survey designations are distinguished from provisional designations by having the letter S in the third character, which contains a decimal digit in provisional designations and permanent numbers.

Permanent packed designations[]

A packed form for permanent designations also exists (these are numbered minor planets, with or without a name). In this case, only the designation's number is used and converted to a 5-character string. The rest of the permanent designation is ignored. Minor planet numbers below 100,000 are simply zero-padded to 5 digits from the left side. For minor planet above 100,000, a single letter (A–Z and a–z) is used, similar as for the provisional subscript number (also see table above):[16]


This system permits compression of numbers up to 619,999 (z99999). As of 2020 the list of minor planets already contains more than half a million numbered bodies.[3] For minor planets numbered 620,000 or higher, a tilde "~" will be used as the first character. The subsequent 4 characters encoded in Base62 (using 0–9, A–Z, and a–z) are used to store the difference of the object's number minus 620,000.[16] This extended system will allow for the encoding of more than 15 million minor planet numbers. For example:

See also[]


  1. ^ a b c d "Provisional Designations – (statistics)". IAU Minor Planet Center. 23 May 2019. Retrieved 5 February 2020.
  2. ^ "Running Tallies – Minor Planets Discovered". IAU Minor Planet Center. Retrieved 5 February 2020.
  3. ^ a b "Minor Planet Statistics – Orbits And Names". Minor Planet Center. 10 July 2017. Retrieved 6 September 2017.
  4. ^ a b c d e "New- And Old-Style Minor Planet Designations". IAU Minor Planet Center. Retrieved 5 January 2017.
  5. ^ a b c "Minor Planet Names: Readme". Institute of Applied Astronomy of the Russian Academy of Sciences. 17 January 2013. Archived from the original on 16 April 2016. Retrieved 5 April 2016.
  6. ^ "Minor Planet Discoverers". Minor Planet Center. 28 December 2015. Retrieved 1 January 2016.
  7. ^ J. Hilton (2001). "When Did the Asteroids Become Minor Planets?". US Naval Observatory (USNO). Archived from the original on 13 November 2011.
  8. ^ "1854AN 38..143 Page 143/144". Adsbit.harvard.edu. Retrieved 2014-06-13.
  9. ^ "1855AN 40..373K Page 373/374". Adsbit.harvard.edu. Retrieved 2014-06-13.
  10. ^ [1][dead link]
  11. ^ Porter, Noah (1884). Webster's Complete Dictionary of the English Language. p. 1780. ISBN 1-881275-24-8.
  12. ^ a b "Temporary Minor Planet Designations". IAU Minor Planet Center. Retrieved 5 January 2017.
  13. ^ Cometary Designation System
  14. ^ "The MPC Orbit (MPCORB) Database". IAU Minor Planet Center. Retrieved 8 January 2017.
  15. ^ "Export Format for Minor-Planet Orbits". IAU Minor Planet Center. Retrieved 8 January 2017.
  16. ^ a b c d e f "Packed Provisional and Permanent Designations". IAU Minor Planet Center. Retrieved 8 January 2017.

External links[]