Voyager Gets Snapshots of Neptune Arcs

The Voyager space probe, continuing to make new discoveries two weeks before its planned close encounter with Neptune, on Friday sent back the first pictures of partial rings called “ring arcs” around the solar system’s fourth-largest planet.

Researchers have long suspected the rings’ existence, but had never seen them from Earth-based telescopes.

The ring arcs, one 30,000 miles long and the other 6,000 miles long, were found in association with two of the four moons of Neptune that were also discovered by Voyager as it neared the end of its 12-year, 2.83-billion-mile journey.

“We’re really just ecstatic,” said Jet Propulsion Lab astronomer Rich Terrile.

Dust, Pebbles, Boulders

Terrile speculated that the newly discovered ring arcs were composed of dust, pebbles, or boulders from moons that have been torn apart or ground down by collisions with other objects in orbit around Neptune. Close-up studies by Voyager as it nears Neptune should help determine their composition more precisely.

The largest arc is just outside the orbit of the newly discovered moon 1989 N4, about 23,300 miles above the planet’s cloud tops. The smaller arc trails moon 1989 N3 by 50,000 miles in its orbit at an altitude of 17,000 miles.

Astronomers had suspected the existence of the rings because light from distant stars would disappear intermittently as the stars passed behind Neptune. But sunlight reflected by the rings is too dim to be seen from Earth.