Provisional designation is the internationally standardized naming convention applied to astronomical objects immediately following their discovery announcement.
In the case of minor planets, more than one provisional designation may be assigned to independent discoveries of an object. Once they are recognized as denoting the same object, one of these (not necessarily the earliest) will be chosen as the primary designation for the object, based on who will get credit for the discovery. The provisional designation is augmented by a permanent designation – a catalog number – once a reliable orbit has been calculated. Provisional designations are superseded by a name in the minority of cases where one is given. , approximately 47% of the more than 1,100,000 known minor planets remain unnumbered, as hundreds of thousands had been discovered in the previous two decades, and 4% of numbered objects have been assigned a name. This system is overseen by the Minor Planet Center of the International Astronomical Union.
Minor planets
The current system of provisional designation of minor planets (asteroids, centaurs and trans-Neptunian objects) has been in place since 1925. It superseded several previous conventions, each of which was in turn rendered obsolete by the increasing numbers of minor planet discoveries.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, possibly, a suffixed number.
Modern provisional designations The modern convention for designating bodies was established in 1925. It includes the year of discovery, a two-letter code that indicates the (half) month and order of discovery within that month, and optionally a numerical suffix once those codes have been used up. For example, the provisional designation (corresponding to 15760 Albion) stands for the 27th body identified during 16–31 Aug 1992: 1992 – the first element indicates the year of discovery. Q – the first letter indicates the half-month of the object's discovery within that year and ranges from A (first half of January) to Y (second half of December), while the letters I and Z are not used (see table below). The first half is always the 1st through to the 15th of the month, regardless of the numbers of days in the second "half". Thus, Q indicates the period from Aug 16 to 31. B1 – the second letter and a numerical suffix indicate the order of discovery within that half-month. The first 25 discoveries of the half-month receive a letter A to Z (excluding the letter I, which is not used to avoid confusion with the digit 1). Because modern techniques typically yield hundreds if not thousands of discoveries per half-month, a subscript number is appended to subsequent discoveries within that half-month to indicate the number of times that the letters A to Z have been cycled through. Thus the suffix 1 indicates discoveries after one completed cycle, namely the 26th through 50th discoveries. Combined with the letter B designating the 2nd discovery in that cycle, B1 indicates the 27th minor planet discovered in the half-month. The packed form of is . First letter A B C D E F G H J K L M N O P Q R S T U V W X Y — 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 A B C D E F G H J K L M N O P Q R S T U V W X Y Z 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 Subscript 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
This scheme is now also used retrospectively for pre-1925 discoveries. For these, the first digit of the year is replaced by an A. For example, A801 AA indicates the first object discovered in the first half of January 1801 (1 Ceres).
Further explanations During the first half-month of January 2014, the first minor planet identification was assigned the provisional designation . Then the assignment continued to the end of the cycle at , which was in turn followed by the first identification of the second cycle, . The assignment in this second cycle continued with , , ... until , and then was continued with the first item in the third cycle. With the beginning of a new half-month on 16 January 2014, the first letter changed to "B", and the series started 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. This idiosyncrasy is not seen, however, in the so-called packed form (packed designation). A packed designation has no spaces. It may also use letters to codify for the designation's year and subscript number. It is frequently used in online and electronic documents. For example, the provisional designation is written as K07Tf8A in the packed form, where "K07" stands for the year 2007, and "f8" for the subscript number 418. 90377 Sedna, a large trans-Neptunian object, had the provisional designation , meaning it was identified in the first half of November 2003 (as indicated by the letter "V"), and that it was the 302nd object identified during that time, as 12 cycles of 25 letters give 300, and the letter "B" is the second position in the current cycle. Survey designations do not follow the rules for new-style provisional designations. For technical reasons, such as ASCII limitations, the numerical suffix is not always subscripted, but sometimes "flattened out", so that can also be written as . A very busy half month was the second half of January 2015 (letter "B"), which saw a total of 15,502 new minor planet identifications . One of the last assignments in this period was and corresponds to the 15,502nd position in the sequence.
Effective numbering limit Because of the limits of the #packed designation, which is the format used in databases, the number of provisional designations was effectively capped at 15,500 per half-month until 2025. This corresponded to an upper limit in the index of 619. January 2015 exceeded this limit; the last assignable designation was (the 15,500th object). The Vera Rubin LSST was expected to find a quarter million minor planets in its most productive months, far beyond the capacity of the packed notation. The MPC therefore developed an extended packed notation, which has allowed them to assign higher provisional designations.New packed provisional designations. Minor Planet Center Newsletter: October 2023. Accessed 2026-03-31. The first provisional designations beyond the new limit were announced in November 2025: and .
Survey designations
Minor planets discovered during the Palomar–Leiden survey and three subsequent Trojan-campaigns, which altogether discovered more than 4,000 asteroids and Jupiter trojans between 1960 and 1977, have custom designations that consist of a number (order in the survey) followed by a space and one of the following identifiers: P-L Palomar–Leiden survey (1960–1970) T-1 Palomar–Leiden Trojan survey (1971) T-2 Palomar–Leiden Trojan survey (1973) T-3 Palomar–Leiden Trojan survey (1977)
For example, the asteroid 6344 P-L is the 6344th minor planet in the original Palomar–Leiden survey, while the asteroid 4835 T-1 (now 20936 Nemrut Dagi) 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 so assign a planetary 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 stylized lance or spear (⚴), 3 Juno a scepter (⚵), and 4 Vesta an altar with a sacred fire (). All had various graphic forms, some of considerable complexity.
It soon became apparent, though, that continuing to assign pictorial symbols was impractical when the number of known minor planets was in the dozens. Johann Franz Encke introduced a new system in the Berliner Astronomisches Jahrbuch (BAJ) for 1854, published in 1851, in which he used numbered planetary disks as symbols. Encke's system began the numbering with Astraea, which was given the numbered symbol ①, and went through Eunomia with ⑪, while Ceres, Pallas, Juno and Vesta continued to be denoted by the original symbols ⚳ ⚴ ⚵ , but in the following year's BAJ, the numbering was reset to start with Ceres, so that Astraea's symbol was changed to ⑤.
The new system found popularity among astronomers, and since then, the permanent designation of a minor planet is a number indicating its order of discovery. Even after the adoption of this system, though, several more minor planets received pictorial symbols, including for 28 Bellona (the morning star and lance of Mars's martial sister); for 35 Leukothea (an ancient lighthouse); and for 37 Fides (a Latin cross). (See Astronomical_symbols#Asteroid_table for more.)
134340 Pluto is an exception: it received a graphical symbol with significant astronomical use (♇), because it was considered a major planet upon discovery, and did not receive a minor-planet number until 2006.
Graphical symbols continue to be used for some minor planets, and assigned for some recently discovered larger ones, mostly by astrologers (see astronomical symbol and astrological symbol). Three centaurs – 2060 Chiron, 5145 Pholus, and 7066 Nessus – and the largest trans-Neptunian objects – 50000 Quaoar, 90377 Sedna, 90482 Orcus, 136108 Haumea, 136199 Eris, 136472 Makemake, and 225088 Gonggong – have relatively standard symbols among astrologers: the symbols for Haumea, Makemake, and Eris have even been occasionally used in astronomy. However, such symbols are generally not in use among astronomers.
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 , 163 Erigone was , 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 followed 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 .