As NASA's New Horizons mission heads to Pluto, scientists could get an idea of what to expect by studying Triton, Neptune's strange icy moon.
New Horizons marked a major anniversary Monday when the Pluto-bound spacecraft crossed the orbit of Neptune: It was 25 years ago that the Voyager 2 spacecraft first flew by Neptune and its satellite Triton.
The Voyager spacecraft's encounter on Aug. 25, 1989, was brief but dramatic: It snapped images of the cold gassy planet and its icy moon, the only time a spacecraft has encountered the distant ice giant. Those images have now been "restored" by Paul Schenk of the Lunar and Planetary Institute in Houston and turned into new global maps and a breathtaking movie.
Schenk said on his blog that he was a post-doc at NASA's Jet Propulsion Laboratory in 1989 and got to watch the cerulean gas giant grow bigger and bigger over several days as Voyager 2 got closer and closer.
"The fantastic cloud patterns of deep blue Neptune were fun, but for Triton, we didn't even know how large it was, so everything was new," Schenk wrote.
New Horizons couldn't fly by Neptune and its moons Monday; Neptune is currently far away. But taking a fresh look at Voyager 2 images of Triton could be very useful for studying New Horizon's target, Pluto. Scientists think that Triton and Pluto are siblings. They're roughly the same size, and both probably came from the Kuiper belt, a ring of icy objects in the outer solar system.
Still, the two objects have had very different stories since then: Pluto has gathered moons of its own, while Triton became a moon, squeezed and stretched by Neptune's gravity until its frigid body erupted with volcanoes.
"What will we see at Pluto? Guesses have ranged from active geology to cold and cratered, so we are in for a suspenseful summer next year!" Schenk wrote. "Triton is of importance as it offers clues to what geologic features might look like on Pluto, given that the icy crusts of both bodies are probably rather similar and would presumably react in similar ways under internal stress and heat."
Schenk thinks it's about time to send another mission to Neptune and Uranus.
"These large bodies are distinct and different from the gas giants Jupiter and Saturn but have been visited only once, by Voyager 2 with instruments designed in the 1970s," Schenk wrote. "What we could learn by going back has been amply demonstrated by the innumerable discoveries of Cassini at Saturn."