Pluto, the most distant planet in the solar system, was discovered in 1930 by Clyde Tombaugh. It was not until 1978 that astronomer James Christy discovered Pluto's moon Charon while observing at the U.S. Naval Observatory in Flagstaff, Arizona. Charon orbits Pluto every 6.4 days. Astronomers like to study Charon, because its orbit around Pluto helps us to learn more about Pluto, like its mass, actual size, and composition.
As part of these studies, Pluto and Charon were imaged by the Hubble Space telescope in May 2005. A team led by Alan Stern of the Southwest Research Institute and Hal Weaver of Johns Hopkins University saw two "stars" that moved with Pluto and also appeared to be orbiting it. There is only one explanation for this -- these "stars" are really two new moons of Pluto!
Moons are very common in the solar system. The only planets without moons are Venus and Mercury. Even many asteroids and other icy objects in the Kuiper Belt have moons.
So congratulations to Pluto on its new moons. The International Astronomical Union will be considering names for the moons (the discovery team gets first crack at appropriate names) in the near future.