Tiny fourth moon discovered in Pluto's orbit

(CNN) - While searching for rings around the dwarf planet Pluto, NASA astronomers made an unintentional discovery - Pluto has a fourth moon.

NASA announced the discovery of the satellite, temporarily named P4, in a news release Wednesday. Astronomers using the Hubble Space Telescope were amazed they could see the moon - believed to be a mere 8 to 21 miles in diameter - from so far away.

"I find it remarkable that Hubble's cameras enabled us to see such a tiny object so clearly from a distance of more than 3 billion miles," said Mark Showalter of the SETI Institute in Mountain View, California. The institute led this observing program with Hubble.