May 19, 1999
Web posted at: 5:18 PM EDT

TUCSON, Arizona (CNN) -- Astronomer Erich Karkoschka of the University of Arizona has discovered an 18th moon orbiting the planet Uranus.

The newly found moon is about 25 miles in diameter. It's called Satellite 1986 U-10, because Karkoschka found it while studying images taken by NASA's Voyager 2 spacecraft in 1986.

"This discovery is very unusual," Karkoschka said in a statement. "Typically, satellites are found within days after the discovery image has been taken. In this case, the discovery image is more than 13 years old."

Because it is so small, the moon was very easy to miss in the Voyager 2 images. It appears as a very faint, almost invisible, dot.

With the discovery of the 18th moon, Uranus is now in a tie with Saturn for the most moons of any planet in our solar system. Jupiter has 16 moons; Neptune has eight; Mars has two; and Earth, Pluto, and the asteroids Ida and Eugenia each have one.

The big question remaining is what the International Astronomical Union will name the moon, now that it has been officially recognized. Many of the other moons of Uranus are named after Shakespeare's ladies -- Belinda, Bianca, Juliet, Rosalind, Ophelia, Cressida, Portia, Cordelia and Desdemona.