Fifth moon spotted near Pluto
United States astronomers have found a fifth moon orbiting far-away Pluto, NASA said.
The irregular-shaped moon, nicknamed S/2012 for now, is about 10 to 24 kilometres across, the US space agency said.
Last year, astronomers reported finding the fourth moon around the icy dwarf planet 5 billion kilometres away.
"The moons form a series of neatly nested orbits, a bit like Russian dolls," Mark Showalter, of the SETI Institute in Mountain View, California, said
Pluto's largest moon, Charon, is 1,030 kilometres across.
The other two, Nix and Hydra, are between 32 and 113 kilometres in diameter, NASA said.
Hubble - a potent space telescope that has transformed the field of astronomy since it was first launched in 1990 - discovered Nix and Hydra in 2005.
Astronomers at the US Naval Observatory glimpsed Charon in 1978.
Pluto, once known as the ninth planet from the Sun, was declassified as a fully fledged planet in August 2006 and joined the new category, dwarf planet.
At about 2,301 kilometres wide, it is about two-thirds the size of the Moon and has a mass less than 1 per cent of the Earth's.