ESA Science & Technology05-Jul-2005 16:50:53

Asteroid Encounters

Asteroid Numbers and Names

The naming of an asteroid is the final step of a long process, which may take decades to complete. It starts when the asteroid is first observed for two consecutive nights by one observer. These results are then sent to the Minor Planet Centre of the International astronomical Union (IAU), which assigns a provisional designation. This is usually a serial number which identifies the observation group, for example 1992 KD.

The provisional designation includes the year of its discovery followed by two letters which give the order of its discovery during that year. Objects discovered between 1 and 15 January are designated, in order of their discovery, AA, AB, AC and so on. Those discovered between 16 and 31 January are given the letters BA, BB, BC etc. The final discoveries of the year, between 16 and 31 December, have designations in the series YA, YB, YC. (The letter J is not used.) So 1992 KD would be the fourth asteroid discovery in the last half of May 1992.

Asteroid moons are given different designations, for example S/1998(45)1 is the first satellite of asteroid (45) to be discovered during 1998.

Once the provisional designation is given, a search for former observations of the asteroid is made. It is possible that different sightings of the same asteroid may have led to it being given many provisional designations over time. When there is enough information to calculate an accurate orbit, a permanent number is assigned to the asteroid.

The Minor Planet Centre in the United States currently has records on the orbits of more than 150 000 asteroids and 1600 comets. Every year, many thousands of asteroids and several dozen comets are discovered, but most of these have not been observed frequently enough for their orbits to be calculated with any accuracy. About 70 000 of the best observed objects, which have fairly well known orbits, have so far been given permanent numbers.

An asteroid with a permanent number will eventually be given a name. The discoverer, the astronomer who first provides enough observations to calculate the orbit with precision, has the privilege of choosing the name. Under this condition, the discoverer is not necessarily the first observer of the asteroid. The proposal is submitted to the Small Bodies Names Committee of the International Astronomical Union, which then makes it official if the proposal is considered to be acceptable.

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