PASADENA, Calif. -- Voyager 2 detected signs of 'southern lights' shimmering above Neptune's atmosphere, scientists said Saturday as the probe beamed back new views of the moon Triton, a frozen wasteland dotted by ancient ice volcanoes.
The best views of Triton were stored on Voyager 2's digital tape recorder during the spacecraft's historic flyby Friday for transmission to Earth on Saturday.
'The spacecraft is doing everything exactly as it was intended to do,' said Mike Urban, a Voyager engineer. 'We spent the night unloading the tape recorder. A lot of the critical information from the encounters of Neptune and Triton were stored on the tape recorder and it takes quite a while to unload that.'
Voyager 2's reel-to-reel digital recorder can store eight tracks of data on a 1,000-foot tape. It takes 21 hours and 14 minutes to play back the entire tape.
Deputy project scientist Ellis Miner said early Saturday that Voyager 2's instruments detected signs of aurora, or southern lights, around 30 degrees south latitude above Neptune's clouds. But he said it was not yet clear whether the lights extended all the way around the planet.
Aurora are created when electrically charged particles spiral along magnetic field lines and interact with a planet's atmosphere. Voyager 2 discovered Neptune's magnetic field several days ago and entered the magnetic bubble around the planet shortly before the flyby late Thursday.
As for Triton, Miner said Voyager 2 had detected nitrogen in the frigid moon's tenuous atmosphere.
With a diameter of a little more than 1,700 miles, Triton is slightly smaller than Earth's moon.
The similarity, however, stops there.
'We have now seen Voyager's last planetary object, Triton, as the spacecraft begins its journey into interstellar space,' Voyager geologist Laurence Soderblom said Friday. 'All we can say now is wow! What a way to leave the solar system!'
At Triton, Voyager 2 detected an alien landscape with polar ice caps -- presumably made up of solid methane or nitrogen -- long intersecting ridges, or cracks, in the icy surface, frozen lakes in ancient calderas and the remains of ice volcanoes that once oozed slushy liquids.
'We have complex geology, we have polar ices, we have peculiar chemistry, we have haze and we have an atmosphere,' Soderblom said. 'For planetary geology this is the end of the beginning, not the beginning of the end.'
Voyager's portrait of Triton depicted features Soderblom compared with volcanic calderas on rocky planets like Venus and Mars.
Material has risen and collapsed within the flat areas at different levels, just as lava rises and collapses to differing levels on volcanoes. But Triton's surface temperature is several hundred chilling degrees below zero.
Voyager 2 darted a scant 3,000 miles over Neptune's frigid cloud tops at 8:56 p.m. PDT Thursday, plunging over the northern polar region and dropping behind the planet as seen from Earth in the spacecraft's fourth and final planetary flyby since launch from Cape Canaveral, Fla., on Aug. 20, 1977.
The nuclear-powered spacecraft, which weighs a ton, plowed through Neptune's magnetic field at a top speed of about 61,150 mph for the close encounter.
Four hours later, Voyager 2 streaked past Triton.
'Even though Voyager has explored dozens of new worlds in the outer solar system, I think without a question the images (of Triton) returned this morning revealed a world unlike any we have ever seen,' Voyager project scientist EdwardStone said Friday.
The bizarre moon orbits Neptune in the opposite direction of the planet's spin, which leads astronomers to suspect it was created elsewhere in the solar system -- and snatched up by Neptune's gravity.
As Triton's orbit slowly stabilized, the moon was pushed and pulled by tidal forces, which heated it up.
Soderblom said Triton featured 'something for everybody' -- a distinctly alien landscape covered by a thin layer of haze over its poles.
Speculating on its origin, Stone said, 'The calculations suggest that after it was captured, tidal heating really melted Triton and kept it liquid for about a billion years. During that time, one would expect a lot of tectonic or geologic activity driven by that strong internal heat source.
'So it's quite likely, under that scenario, that Triton was at one time a geologically active object. But not today,' Stone said. 'What we're seeing is the frozen imprint of that era covered over by (frost and ice) that move around.'
While the moon cooled, it did so from the surface inward, creating a crust of ice overlying less solid, perhaps slushy material. As the interior of the planet cooled, water could have frozen, expanded and cracked the crust, allowing slush to flow up and out to create the ridges and frozen lakes seen by Voyager 2.