Washington, July 21 (IANS) Astronomers have discovered a fourth moon orbiting the icy dwarf planet Pluto, the NASA has announced.

The tiny, new satellite - temporarily designated P4 - was uncovered in a survey using the Hubble space telescope, searching for rings around the planet, Xinhua reported.

P4 was first seen in a photo taken with Hubble's Wide Field Camera 3 June 28. It was confirmed in subsequent Hubble pictures taken July 3 and July 18.

It is the smallest moon discovered orbiting Pluto. It has an estimated diameter of 13 to 34 km. By comparison, Charon - Pluto's largest moon - is 1,043 km across, and the other moons, Nix and Hydra, are in the range of 32 to 113 km in diameter.

"I find it remarkable that Hubble's cameras enabled us to see such a tiny object so clearly from a distance of more than three billion miles (or five billion km)," said Mark Showalter of the SETI Institute in California, who led the programme.

P4 is located between the orbits of Nix and Hydra, which Hubble discovered in 2005.

Charon was discovered in 1978 at the US Naval Observatory and first resolved using Hubble in 1990 as a separate body from Pluto.