NASA's Hubble Telescope has discovered a new fourth moon orbiting the ice-world planet Pluto.

According to a recent press release from NASA, using the Hubble Telescope Astronomers were able to discover the new fourth moon while searching for rings around the planet.

Currently designated "P4" the moon is the smallest of the four with NASA scientists estimating it to have an eight to 21 mile diameter. This compares to Pluto's largest moon Charon's 638 mile diameter.

Mark Showalter, the lead scientist in the SETI Institute in Mountain View observing project commented on the discovery: "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)."

The new moon was found between the orbits of Pluto's Nix and Hydra moons -- both of which were discovered in 2005. The largest moon Charon was discovered earlier in 1978.

Like its other moons, P4 is believed to have been formed after another planet sized object collided with Pluto. The planet's moons are believed to be the largest chunks of debris that resulted from the collision.

The observation project is a part of NASA's ongoing New Horizons mission. The mission is scheduled to fly through Pluto's system in 2015 and is intended to provide new insights about the planets at the solar system's rim.

P4's existence was first suspected when one of the Hubble's camera photographed it late last month. Its existence was subsequently confirmed when the Hubble caught two more images of it on 3 July and 18 July.

Jon Morse, astrophysics division director at NASA Headquarters in Washington commented on the photos: "This surprising observation is a powerful reminder of Hubble's ability as a general purpose astronomical observatory to make astounding, unintended discoveries."