The Naming of Asteroids

Cometary history

They used to be discovered perhaps once every ten years; now, telescopes have taken us into a new era in cometary history.

Toutatis

The September Stardate is called Close Encounters, and it marks the orbit of the asteroid Toutatis coming close to the Earth. Find out more about our visitor Toutatis.

Threat or blessing?

If an asteroid heads our way, should we take evasive action - or grab our mining equipment? Do we avoid or exploit?

Fear in the skies?

While many asteroids break up when they hit Earth's atmosphere, when larger bodies head towards earth, they can do real damage. Just ask the dinosaurs. But are the risks just Hollywood hype, or is there real fear in the skies?

Which one is that?

With so many objects hurtling about, how do we know which is which? The system isn't foolproof, but at least there are agreements on asteroid registering and tracking.

How do asteroids get their names?

The first asteroids to be discovered were given names from classical mythology, such as Ceres, Juno, Pallas and Vesta. The International Astronomical Union (IAU) now regulates the naming of asteroids. Names are no longer restricted to mythological characters, but must be inoffensive and not connected with recent political or military activity.

However, no asteroid is awarded a name until it has been observed long enough for its orbit to be determined with a fair degree of precision. This may take several years, but when it is achieved the body is awarded a “permanent designation” (a number issued in strict numerical sequence) and the discoverer is invited to suggest a name for approval by a special committee of the International Astronomical Union.

Strictly speaking, Ceres, the first known asteroid, is known as (1) Ceres. Examples of more unusual or whimsical names include (7758) Poulanderson (named after a science fiction author), (8749) Beatles (named after the 1960s pop group), and (5460) Tsenaat'a'i (which means “flying rock” in the Navaho language).

The prize for the most imaginative name goes to (2037) Tripaxeptalis. The name is pure invention but sounds like “triPax-septAlice”, which reflects the fact that its permanent designation is three times that of (679) Pax and seven times that of (291) Alice.

Until its orbit has been sufficiently well-documented, each new discovery is known only by a “provisional designation” consisting of the year of discovery followed by two letters and, if necessary, numbers that relate more precisely to the date and sequence of discovery.

For example, the asteroid (4179) Toutatis was discovered in early January 1989 and initially had the provisional designation 1989 AC, in which the first letter (A) signifies that it was discovered during the period January 1-15 and the second letter (C) shows that it was the third discovery during that period. The letter I is not used in this convention, so the remaining 25 letters of the alphabet enable 25 asteroids to be designated during each half-month period. When this number is exceeded, the letter code sequence is repeated as any times as necessary with a numerical subscript that is incremented every 25 discoveries (so that 1989 AC₁ would indicate the 28th discovery during the first half of January 1989).

Content last updated: 04/08/2004

About our expert

Dave Rothery is a volcanologist and planetary scientist at the Open University. His current research includes studying volcanic eruptions on the Earth and the characterising planetary surfaces. He chairs the OU's planetary science courses and the geology residential school course.