Provisional designation

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fr:Désignation des astéroïdes

The provisional designation of comets and asteroids are similar to each other: they both follow a pattern set by the Minor Planet Center of the IAU.

The basis of the modern system retains features of the older system. The key components include:

1. The year of the observation
2. (a blank space)
3. A letter indicating the half-month of discovery (see table, below)
4. A number for a comet, a second letter for an asteroid (I omitted, but Z is used!)
5. Comet numbers continue indefinitely, but for an asteroid, a peculiar subscripting notation continues, assuming the first pass through the alphabets had implicit subscript 0. The second pass through uses 1, third 2, etc.

Comets are prefixed with C/ D/ P/ X/ depending on the type of comet orbit (or if it is now e"x"tinct). Asteroids can be prefixed with A/ but usually are not.

Examples

In the year 2004, the first asteroid discovery of January 1 would be named 2004 AA. Then the naming continues through 2004 AZ, followed by 2004 AA₁. Partly for technological reasons (ASCII limitations), the subscript is often "flattened out", so 2004 AA₁ is written 2004 AA1. The next discovery is 2004 AB1, then 2004 AC1, etc. Eventually one could get to something like 2004 AA276, BUT only if the calendar date has not passed to January 16. At that point, the system jumps onward to 2004 BA.

The object known as "90377 Sedna" had the provisional designation 2003 VB₁₂, meaning it was discovered in the first half of November 2004, and that it was the 302^nd object (B->2 + 12*25 = 302) discovered during that time. 28978 Ixion, originally 2001 KX₇₆, was discovered in the latter half of May 2001, and was the (X->23 + 76*25 = 1923) 1,923^rd object discovered during that time.

Comet discoveries work similarly. 2004 A1 is the first comet of January 1-15. 2004 A2 is the second, and so forth.

Many objects originally seen as asteroidal may develop clear tails and become comets. In that case they retain their asteroid designation with two letters, but gain the comet prefix C/ D/ or P/ as appropriate.

Packed Designations

Clearly the system isn't sorted well, so a 'translation' is used for indexing long lists. First, the year is written out using a single letter code for the century (18 = I, 19 = J, 20 = K, and so on; the first century would theoretically be 00 = A) and the last two digits in clear. Thus 2004 AA starts off as K04. Next, the implicit subscript becomes explicit and is inserted between the letters so the first pass sorts before the second pass. Thus 2004 AA becomes K04A00A, 2004 AA1 becomes K04A01A, and so on. The use of a two digit field (00 through 99) would have originally been enough, but in the late 1990's so many discoveries resulted that a hexadecimal-like notation had to be adopted for the tens, where A=10, B=11, etc. This first occurred with (17810) 1998 FM₁₀₀. Thus 2004 AZ99 becomes K04A99Z and 2004 AA100 becomes K04AA0A. This can continue through Z=35, so 2004 AZ359 becomes K04AZ9Z - the highest possible packed designation in this scheme.

The beginning of the 2000's led to 360 passes through the alphabet requiring a further adaptation. This first occurred with (62643) 2000 SH₃₆₀. The scheme adopted was to set a=36, b=37, etc. This also sorts well in ASCII but loses the all-capitals and might cause case problems. This system currently ends at the equivalent of 2004 AZ619 with z=61. The highest count reached as of 2004 was 2000 SA₃₇₂. Thus, 2004 AA360 becomes K04Aa0A and 2004 AZ619 becomes K04Az9Z.

Comets are 'packed' similarly, but rarely create problems as the objects now are often discovered first appearing as asteroidal. They are packed such that a zero takes the place of the missing letter at the end. Thus 2004 A22 becomes K04A220. Were comet discoveries to "roll over" past 2004 A99 (K04A990), the same system would assign 2004 A100 as K04AA00 all the way to 2004 A619 as K04Az90.