Minor planet designation facts for kids

Minor planet designations are special codes given to small objects in space, like dwarf planets and asteroids. These codes are assigned by the Minor Planet Center, which is part of the International Astronomical Union (IAU). Think of them like official names and numbers for these space rocks!

These designations are given once an object's path around the Sun (its orbit) is well understood. They are different from "provisional designations," which are temporary names given when an object is first discovered. Comets also get names, but they use a different system.

A formal designation has two parts:

• A number: This number used to be given in the order the object was found. Now, it's given only after its orbit is confirmed.
• A name: This can be a name chosen by the astronomer who found it, or sometimes it's just the provisional designation.

It usually looks like this: (number) Name. For example, (90377) Sedna. Sometimes, the brackets around the number are left out, like 90377 Sedna, if the astronomer prefers it that way. For well-known objects, people often just use the name, like Sedna, instead of the full designation.

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

How Minor Planets Get Their Names

Early Days of Asteroid Naming

By the year 1851, astronomers had found 15 asteroids. Each of these asteroids had its own special symbol. But these symbols were becoming very complicated and hard to draw by hand. Imagine having to draw a tiny, detailed picture every time you wanted to write about an asteroid!

A Simpler Way to Identify Space Objects

To solve this problem, an astronomer named Benjamin Apthorp Gould had a great idea in 1851. He suggested numbering the asteroids in the order they were discovered. He also said that this number could be put inside a circle to be the asteroid's symbol. So, the fourth asteroid found, Vesta, would have the symbol ④.

This new numbering system quickly became popular. Soon, the number was combined with the asteroid's name to create an official designation, like "④ Vesta." As more and more minor planets were discovered, this system became even more important.

Around 1858, the circle around the number was changed to brackets, like "(4)" or "(4) Vesta." This was much easier to print in books and papers. Other ways of writing it, like "4) Vesta" or "4, Vesta," were also used for a while but mostly disappeared by 1949.

The Pluto Exception

There's one big exception to the rule that the number shows the order of discovery or orbit calculation: Pluto. Pluto was first thought to be a full planet, so it didn't get a number. But in 2006, scientists changed the definition of a "planet." Pluto didn't fit the new definition anymore, so it was reclassified as a dwarf planet. At that point, Pluto was given the formal designation (134340) Pluto.