Minor-planet designation Facts for Kids

A minor-planet designation is like an official name and number for small objects in space, such as asteroids, centaurs, trans-Neptunian objects, and dwarf planets. It's not used for comets, which have their own system. This designation always starts with a number, called a catalog or IAU number. This number is given once an object's path around the Sun (its orbit) is very well known. This process is called "numbering."

Before an object gets its official number, it receives a provisional designation. This is a temporary name given automatically when the object is first seen. Later, if the object gets a permanent name, this provisional part is replaced. This process is called "naming." Both the official and temporary designations are managed by the Minor Planet Center (MPC), which is part of the International Astronomical Union.

An object usually gets a number after its orbit has been carefully watched during at least four "oppositions." An opposition is when the object, Earth, and the Sun are lined up, making the object easy to see. For unusual objects, like near-Earth asteroids, they might get a number after only two or three oppositions. As of 2020, over half a million minor planets have received a number. However, only about 20,000 (or 4%) of these have also received a name. Around 500,000 minor planets haven't even been numbered yet!

Even moons that orbit minor planets have a special naming system. For example, the moon of the asteroid Sylvia is called (87) Sylvia I Romulus. This system uses Roman numerals, similar to how moons of planets have been named since Galileo's time.

How Minor Planets Get Their Names

An official designation has two main parts: a number and either a name or a provisional designation. The number is usually given in the order the object was discovered or its orbit was confirmed. The name is typically chosen by the person who discovered it.

Here's how the official names look:

For minor planets that haven't been named yet: `(number) Provisional designation`
For minor planets that have been named: `(number) Name` (sometimes the parentheses around the number are left out).

For example, an unnamed minor planet might be called `(388188) 2006 DP14`. The number `388188` is always in parentheses. But for a named minor planet like `(274301) Wikipedia`, the parentheses might be dropped, so you might just see `274301 Wikipedia`. Big databases like the JPL Small-Body Database often leave out the parentheses for named objects.

The names of minor planets can change over time. When the asteroid 274301 Wikipedia was found in August 2008, its temporary name was `2008 QH24`. After its orbit was confirmed, it became `(274301) 2008 QH24`. Then, on January 27, 2013, it was officially named Wikipedia in the Minor Planet Circulars.

Depending on who is writing and when, you might see `274301 Wikipedia` referred to as `2008 QH24` (its provisional name) or simply `(274301)` (its number). For well-known objects, the number is mostly for record-keeping. People usually use the name or provisional designation instead. For instance, Pluto is almost never called `134340 Pluto`. Similarly, `2002 TX300` is more commonly used than the longer `(55636) 2002 TX300`.

The History of Naming Space Rocks

By 1851, astronomers knew about 15 asteroids. Each of these had its own special symbol. But as more and more asteroids were found, these symbols became very complicated and hard to draw by hand.

To solve this problem, a scientist named Benjamin Apthorp Gould suggested a new system in 1851. He thought asteroids should be numbered in the order they were discovered. This number would be placed inside a circle to be the asteroid's symbol, like ④ for the fourth asteroid, Vesta. Soon, this number was combined with the asteroid's name, creating an official "④ Vesta" designation.

As even more minor planets were found, the circle around the number was simplified to parentheses, like "(4)" or "(4) Vesta." This made it much easier to print. Other ways of writing it, like "4) Vesta" or "4, Vesta," were also used for a while but mostly disappeared by 1949.

There's one big exception to this numbering rule: Pluto. When Pluto was first discovered, it was thought to be a planet. So, it wasn't given a number like other minor planets. But in 2006, scientists changed the definition of a "planet," and Pluto no longer fit. At that point, Pluto was given the official minor-planet designation `(134340) Pluto`.

Minor-planet designation facts for kids

How Minor Planets Get Their Names

The History of Naming Space Rocks

See also