BBC News

Five new satellites - and one candidate moon - have been discovered orbiting the giant planet Neptune, bringing its tally of moons to 13.

Two orbit in the same direction as the planet rotates, while the orbits of the others are opposite to Neptune's spin.

The tiny outer satellites are probably captured asteroids, astronomers say.

Cataclysmic events connected to the capture of Neptune's moon Triton were thought to have destroyed any outer satellites the planet once had.

The new moons, named S/2002 N1 to N4 and S/2003 N1, are in eccentric, tilted orbits. They are all between 30km and 50km in diameter.

An international team of astronomers searched for the satellites between 2001 and 2003 using the 4m Cerro Tololo Inter-American Observatory and the 3.6m Canada-France-Hawaii telescope.

Elusive sixth

The researchers used a technique to look for the new moons that was originally developed to detect very faint objects in the outer Kuiper Belt.

They also observed a sixth candidate moon, which they have named c02N4. This was discovered on 14 August 2002 and seen again at the Very Large Telescope (VLT) on 3 September 2002. But further attempts to spot this object failed.

The researchers say this could be Centaur - an object that has migrated from the outer Kuiper Belt. But its lack of movement relative to Neptune is more consistent with it being a satellite.

The satellites are unlikely to have condensed from material around Neptune.

Instead, these so-called irregular moons may be the product of a parent body that collided with Neptune's moon Nereid and were then disturbed in their orbits by the capture of Triton from the Kuiper Belt.