PASADENA, Calif. -- NASA's Voyager 2 probe, hurtling toward an historic flyby of Neptune Aug. 24, has discovered a pair of strange, partial rings around the mysterious planet, possibly the remains of destroyed moons, elated scientists say.
Images of the faint 'ring arcs' were received Friday at the Jet Propulsion Laboratory, confirming predictions based on scanty Earth-based observations and bringing to four the number of known planets girdled with ring systems.
'We're certainly excited,' assistant Voyager project scientist Ellis Miner said in an interview. 'You can actually see a curved arc cross the picture and it describes something like an eighth of a complete circle.'
Miner said it was too soon to say what might have created the ring arcs, although it is probable they are made up of debris from 'moons that have been broken up and we're seeing debris trails.'
Launched nearly 12 years ago from the Cape Canaveral Air Force Station in Florida, Voyager 2 will race just 3,000 miles above Neptune's cloudtops at midnight EDT on Aug. 24 for the spacecraft's final planetary encounter in a once-in-a-lifetime grand tour of the outer solar system.
Along the way, the hardy probe has explored Jupiter, Saturn and Uranus, all three of which have well-developed ring systems.
Prior to the current encounter, there was controversial Earth-based evidence for the existence of partial rings around Neptune and the discovery of the two ring arcs Friday marked a major milestone in Voyager's exploration of the distant planet.
Miner said both newly discovered ring arcs appear to be associated with two of four new moons that were discovered by Voyager 2 earlier this summer. Two moons, Triton and Nereid, were known before the encounter.
One arc stretches 30,000 miles and circles Neptune just outside the orbit of a moon temporarily dubbed 1989 N4, which orbits about 23,300 miles above Neptune's cloud tops.
The second arc stretches some 6,000 miles and appears to trail the moon 1989 N3 by about 90 degrees, or 50,000 miles. 1989 N3 orbits Neptune at an altitude of about 17,000 miles.
'It doesn't look much like what we predicted,' Miner said. 'We had predicted very short arcs and possibly several of them along any given radius of the planet.'
He said it was not clear whether the moons were 'shepherding' the ring arcs along as is the case with rings around Uranus and Saturn, or if their gravity merely serves to collect dust and debris in their wake.
'It's a little hard to tell right now whether they're actually shepherding or whether they are collecting debris around them,' he said. 'The analysis remains to be done to see how close they are to the orbits of these moons.'
The arcs were discovered in 8-minute exposures by Voyager 2's camera system and more are expected to be discovered as the spacecraft gets closer to Neptune.