In August 25, 1989, Voyager 2, which had been flying through the outer solar system for over a decade, passed by Neptune’s moon Triton before voyaging away, heading outside our solar system. NASA announced on Thursday that Paul Schenk, a scientist at the Lunar and Planetary Institute in Houston, has digitally restored the old footage of the flyby and has produced a map of that part of Triton that was illuminated by the distant sun. As a bonus, Schenk also produced a brief movie of the close encounter.
Triton, at 1,680 miles in diameter, is the largest of the known moons of Neptune. Unlike most moons it orbits its host planet in a retrograde orbit, which is to say the opposite direction from the rotation of Neptune. This is likely because Triton started as a “dwarf planet” much as Pluto is now designated and was captured by Neptune sometime in the distant past.
Because of its proximity to Neptune, tidal forces are heating Triton’s core. As a result there are volcanos, fractures, and other features that suggest geological activity, Triton has a thin nitrogen atmosphere, likely as result of outgassing through volcanos. Thus, even though they are both dwarf planets, Triton is not likely a twin of Pluto, which remains isolated enough to remain in a deep freeze. However the surfaces of both bodies contain The surface composition of both worlds contains carbon monoxide, carbon dioxide, methane and nitrogen ices.
The map of Triton is incomplete because half of the moon was pointed away from the sun as Voyager 2 flew by it and was thus shrouded in darkness. A closer examination of Triton and the rest of Neptune’s system will have to await the arrival of a Cassini/Galileo class orbiter. Though such a probe has been discussed by the planetary science community, the concept has not gotten any funding and is unlikely to get a new start anytime soon.