Provisional designation in astronomy

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

• 2016 – the first element indicates the year of discovery.
• E – 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, E indicates the period from March 1 to 15.[4][5]
• K₁₅₆ – the second letter and a numerical suffix indicate the order of discovery within that half-month. The first 25 discoveries of the half-month only receive a letter (A to Z) without a suffix, while the letter I is not used (to avoid potential confusions with the digit 1). Because modern techniques typically yield hundreds if not thousands of discoveries per half-month, the subscript number is appended to indicate the number of times that the letters from A to Z have cycled through. The suffix 156 indicates 156 completed cycles (156 cycles × 25 letters = 3900), while K is the 10th position in the current cycle. Thus, K₁₅₆ stands for the 3910th minor planet discovered in a half-month.
• The packed form of 2016 EK₁₅₆ is written as K16EF6K.

• During the first half-month of January 2014, the first minor planet identification was assigned the provisional designation 2014 AA. Then the assignment continued to the end of the cycle at 2014 AZ, which was in turn followed by the first identification of the second cycle, 2014 AA₁. The assignment in this second cycle continued with 2014 AB₁, 2014 AC₁, 2014 AD₁... until 2014 AZ₁, and then was continued with 2014 AA₂ 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 2014 BA.
• 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 2007 TA₄₁₈ 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 2003 VB₁₂, 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 1989 SG₁ can also be written as 1989 SG1.
• A very busy half month was the second half of January 2015 (letter "B"), which saw a total of 14,751 new minor planet identifications. One of the last assignments in this period was 2015 BA₅₉₀ and corresponds to the 14,751st position in the sequence.[1]

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]

• 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 was discovered during the first Trojan-campaign. The majority of these bodies have since been assigned a number and many are already named.

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 (, later became a star with a crossed handle, ⚵) and 4 Vesta a sacred fire altar ().[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 ().[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.

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 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]

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).

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.)

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.

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

• uses exactly 7 characters with no spaces for all designations
• compacts 4 digit years to a 3-character code, e.g. 2014 is written as K14 (see tables below)
• converts all subscript numbers to a 2-character code (00 is used when there is no following subscript, 99 is used for subscript 99, A0 is used for subscript 100, and A1 is used for 101)
• the packed 2 character subscript code is placed between the half-month letter and the second (discovery order) letter (e.g. 2016 EK₁₀₂ has discovery order K₁₀₂ so the last three characters for its packed form are A2K)

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]

Examples

Description

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

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

• 6344 P-L is written as PLS6344
• 4835 T-1 is written as T1S4835
• 1010 T-2 is written as T2S1010
• 4101 T-3 is written as T3S4101

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.

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]

• A covers the number range 100,000–109,999
• B covers the number range 110,000–119,999
• a covers the number range 360,000–369,999
• z covers the number range 610,000–619,999

Examples

• 00001 encodes 1 Ceres
• 99999 encodes (99999) 1981 FP
• A0000 encodes 100000 Astronautica, (as A0= 100K)
• A9999 encodes (109999) 2001 SZ₆₂ (as A9= 109K)
• B0000 encodes (110000) 2001 SM₆₃ (as B0= 110K)
• G3693 encodes 163693 Atira (as G3= 163K)
• Y2843 encodes 342843 Davidbowie (as Y2= 342K)
• g0356 encodes 420356 Praamzius (as g0= 420K)

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:

• (620000) will be represented as ~0000 (620,000 − 620,000 = 0 = 0 × 62³ + 0 × 62² + 0 × 62¹ + 0 × 62⁰)
• (620061) will be represented as ~000z (620,061 − 620,000 = 61 = 0 × 62³ + 0 × 62² + 0 × 62¹ + 61 × 62⁰)
• (3140113) will be represented as ~AZaz (3,140,113 − 620,000 = 2,520,113 = 10 × 62³+ 35 × 62² + 36 × 62¹ + 61 × 62⁰)
• (15396335) will be represented as ~zzzz (15,396,335 − 620,000 = 14,776,335 = 61 × 62³ + 61 × 62² + 61 × 62¹ + 61 × 62⁰)