Provisional Designations


Unpacked Provisional Designations

This section describes the formats for both new-style provisional designations for minor planets (as used from the start of 1925) and the old-style designations (as used prior to 1925).

Current Provisional Designations (Post-1925)

The Minor Planet Center assigns new provisional designations when an object cannot be identified immediately with some already designated object and the orbit of the object is good enough to not require immediate additional follow-up.

The standard designation consists of the following parts, all of which are related to the date of discovery of the object: a 4-digit number indicating the year; a space; a letter to show the half-month; another letter to show the order within the half-month; and an optional number to indicate the number of times the second letter has been repeated in that half-month period.

The half-month of discovery is indicated using the following scheme:

  Letter     Dates             Letter      Dates
    A      Jan. 1-15             B       Jan. 16-31
    C      Feb. 1-15             D       Feb. 16-29
    E      Mar. 1-15             F       Mar. 16-31
    G      Apr. 1-15             H       Apr. 16-30
    J      May  1-15             K       May  16-31
    L      June 1-15             M       June 16-30
    N      July 1-15             O       July 16-31
    P      Aug. 1-15             Q       Aug. 16-31
    R      Sept.1-15             S       Sept.16-30
    T      Oct. 1-15             U       Oct. 16-31
    V      Nov. 1-15             W       Nov. 16-30
    X      Dec. 1-15             Y       Dec. 16-31

             I is omitted and Z is unused
The order within the month is indicated using letters as follows:
    A = 1st     B = 2nd     C = 3rd     D = 4th     E = 5th
    F = 6th     G = 7th     H = 8th     J = 9th     K = 10th
    L = 11th    M = 12th    N = 13th    O = 14th    P = 15th
    Q = 16th    R = 17th    S = 18th    T = 19th    U = 20th
    V = 21st    W = 22nd    X = 23rd    Y = 24th    Z = 25th

                        I is omitted
If there are more than 25 discoveries in any one half-month period, the second letter is recycled and a numeral '1' is added to the end of the designation. If there are more than 50 discoveries, the second-letter is again recycled, with a numeral '2' appended after the second letter. Discoveries 76-100 have numeral '3' added, numbers 101-125 numeral '4', etc. When possible, these additional numbers should be indicated using subscript characters.

Thus the order of assignment of designations in a particular half-month period is as follows: 1995 SA, 1995 SB, ..., 1995 SY, 1995 SZ, 1995 SA1, ...,1995 SZ1, 1995 SA2, ..., 1995 SZ2, ..., 1995 SA10,..., 1995 SZ10, etc.

This scheme has been extended to pre-1925 discoveries--such designations are indicated by the replacement of the initial digit of the year by the letter `A'. Thus, A904 OA is the first object designated that was discovered in the second half of July 1904.

Survey Designations

Four special surveys, undertaken between 1960 and 1977, have designations that consist of a number (identifing the order within that survey), a space and a survey identifier. The survey identifiers are as follows:
   Survey                         Identifier
   Palomar-Leiden (1960)             P-L
   First Trojan Survey (1971)        T-1
   Second Trojan Survey (1973)       T-2
   Third Trojan Survey (1977)        T-3
Example designations are 2040 P-L, 3138 T-1, 1010 T-2 and 4101 T-3.

Old-Style Provisional Designations (Pre-1925)

In the first half of the 19th century, minor planets were referred to simply by name. The assignment of ordinal numbers, ostensibly in order of discovery, was introduced in the early 1850s. Initially, new numbers were assigned by the editors of the Astronomisches Nachrichten (AN) immediately upon receipt of the announcement of a new discovery from an observer.

In 1892 a system of provisional designations was introduced by the AN. A definitive number was subsequently given by the editors of the Berliner Astronomisches Jahrbuch to those objects for which reasonable orbital elements had been computed. The provisional designation scheme consisted initially of a year and a single letter: e.g., 1892 A, 1892 B, etc., omitting the letter 'I'.

In 1893, the 25 available letters proved to be insufficient and a series of double letter designations was introduced: e.g. 1893 AA, 1893 AB, etc., omitting the letter 'I'. The sequence of double letters was not restarted anew each year, so 1894 AQ followed 1893 AP (for example). 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.

[NOTE: In old publications, it is common to see 'J' as the omitted letter instead of 'I'--the sequence going 1892 H, 1892 I, 1892 K, etc. Modern usage would consider 1892 I to be the same as 1892 J and it is this latter designation which is recorded.]

In the double-letter scheme it was not generally possible to insert new discoveries into the sequence once designations had been assigned in a subsquent 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 in order to distinguish this designation from the old-style comet designation 1915a), 1917 b. In 1914 designations of the form year plus Greek letter were used in addition.

During World War I the active observers at Simëis in the Crimea, deprived of official designations for their discoveries, assigned their own. The designations came in two forms: year + Greek capital sigma + letter(s); Greek capital sigma + number. The Greek capital sigma is indicated as SIGMA.

Other designation schemes used at Simëis and other observatories are listed on a different page.

To summarise, the following forms of input are valid:

  • Year + Single Letter: 1892 A
  • Year + Double Letter: 1914 VV
  • Year + letter: 1913 a
  • Year + Greek letter: 1914 gamma
  • Year + SIGMA + letter: 1915 SIGMA r, 1916 SIGMA ci
  • SIGMA + number: SIGMA 27
For the purposes of searching, SIGMA may be abbreviated to SIG and the year is optional on the year+SIGMA+letter designations (i.e., SIGMA ci is a shorthand form for 1916 SIGMA ci).

Packed Provisional Designations

The Minor Planet Center (MPC) uses packed provisional designations to communicate designation information within the orbit and observations (MPC1992 80-character) format.

Original Packed Provisional Designation Scheme

The first two digits of the year are packed into a single character in column 1 (I = 18, J = 19, K = 20). Columns 2-3 contain the last two digits of the year. Column 4 contains the half-month letter and column 7 contains the second letter. The cycle count (the number of times that the second letter has cycled through the alphabet) is coded in columns 5-6, using a letter in column 5 when the cycle count is larger than 99. The uppercase letters are used, followed by the lowercase letters.

Where possible, the cycle count should be displayed as a subscript when the designation is written out in unpacked format.

   J95X00A = 1995 XA
   J95X01L = 1995 XL1
   J95F13B = 1995 FB13
   J98SA8Q = 1998 SQ108
   J98SC7V = 1998 SV127
   J98SG2S = 1998 SS162
   K99AJ3Z = 2099 AZ193
   K08Aa0A = 2008 AA360
   K07Tf8A = 2007 TA418
Survey designations of the form 2040 P-L, 3138 T-1, 1010 T-2 and 4101 T-3 are packed differently. Columns 1-3 contain the code indicating the survey and columns 4-7 contain the number within the survey.
   2040 P-L  = PLS2040
   3138 T-1  = T1S3138
   1010 T-2  = T2S1010
   4101 T-3  = T3S4101

Extended Packed Provisional Designation Scheme

As described in [Add link to newsletter], the packing-format described in Original Packed Provisional Designations that was originally chosen for the packed provisional designations has hitherto been limited to supporting only 15,500 new designations per half month (the standard unpacked designations described in Unpacked Provisional Designations have no such restrictions). When the Vera Rubin LSST commences operations, it is estimated that during its most productive months, approximately 250,000 objects will be discovered. To allow the community to continue using the orbit and observations files containing the packed provisional designation format while accommodating the predicted volume of LSST discoveries, the MPC is extending the packing-format as described below.

When more than 15,500 objects are designated within a half-month, designations will be indicated as follows:

  • The first character must be an underscore, simultaneously indicating (a) the use of the extended packed provisional format, and (b) that the first 2 digits of the year of discovery are 20.
    • N.B. This implies that the extended packed provisional designation format will not be applied to objects discovered prior to 2010 (see bullet point below for the encoding of the last two digits of the year).
  • The second character must be a capital letter (indicating the last 2 digits of the year of discovery, where 'P' = 25, 'Q' = 26, etc).
    • N.B. This encoding scheme is the same as that used for the first two digits of the year in the Original Packed Provisional Designations format. This implies that this extended packed provisional designation format is not expected to be employed beyond 2035 (as 'Z' = 35).
  • The third character is the capital letter for the half month.
  • Four alphanumeric characters [0-9A-Za-z] will be used as a base62 representation of the order of designation after 15,500.
    • N.B. This implies subtracting 15,501 from the sequence-number before converting to base-62 representation used
    • The base-62 representation uses the digits 0-9 to represent numbers from 0-9, then upper-case letters A-Z to represent numbers between 10 and 35 inclusive, then lower case letters a-z to represent numbers between 36 and 61 inclusive.

As such:

  • The 15,500th object designated in half-month “C” of 2026 will be 2026 CZ619 == K26Cz9Z
  • The 15,501st object designated in half-month “C” of 2026 will be 2026 CA620 == _QC0000
  • The 154,775th object designated in half-month “C” of 2026 will be 2026 CZ6190 == _QC0aEM
  • The final object designated in half-month “C” of 2026 that can be accommodated in this extended format will be number 14,791,836, i.e. 2026 CL591673 == _QCzzzz. This seems likely to be sufficient.

Some example designations are provided below to help elucidate the packed provisional designation in a variety of cases.

Year Half Month Order of Designation within Half Month
Order of Designation within Half Month
Order of Designation within Half Month
[Number minus 15501]
Unpacked Provisional Designation Packed Provisional Designation
2023 B 0 A - 2023 BA K23B00A
2024 C 100 Z3 - 2024 CZ3 K24C03Z
2025 D 15500 Z619 - 2025 DZ619 K25Dz9Z
2025 D 15501 A620 0 2025 DA620 _PD0000
2026 D 15524 Y620 23 2026 DY620 _QD000N
2027 E 154775 Z6190 139274 2027 DZ6190 _RD0aEM
2028 E 8493726 A339749 8478225 2028 EA339749 _SEZZZZ
2029 F 14791836 L591673 14776335 2029 FL591673 _TFzzzz

The MPC will not publish any designations using this extended packed provisional designation format before June 2024. After that date the MPC will begin publishing designations in the extended format as necessary in any publications.