Hubble Telescope Finds a New Moon Orbiting Pluto

BY Jenny Marder  July 21, 2011 at 1:41 PM EST

The Hubble Space Telescope peered 3 billion miles into space and found a fourth, previously unseen moon orbiting Pluto.

As moons go, it is tiny — only an estimated 8 to 21 miles across, compared to Pluto’s largest moon, Charon, which is 648 miles across. It is located between Nix and Hydra, which range from 20 to 70 miles.

The new moon was first seen on June 28 in a photo taken with Hubble’s Wide Field Camera 3 and confirmed in subsequent Hubble pictures taken on July 3 and July 18. For now, scientists are calling it P4.

“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 (5 billion km),” said Mark Showalter of the SETI Institute in Mountain View, Calif., who led the observing program with the Hubble.

Pluto was long considered the ninth planet in our solar system, but was reclassified as a dwarf planet in 2006. The downgrade came after the word “planet” was for the first time defined as an object in the solar system that must be round, must orbit a star, and must clear out its neighborhood.