WHAT WE LEARNED ABOUT NEPTUNE

Neptune, which is blue in color because of methane in its atmosphere, has a dynamic atmosphere with winds up to 700 m.p.h. and a storm center as large as the entire Earth. That was completely unexpected.

The planet has a magnetic field, but it is tipped 50 degrees from Neptune’s rotational axis. No one is sure why.

Neptune’s magnetic field indicates that the planet’s day is 16.3 hours long, about two hours shorter than scientists had thought.

Voyager discovered six previously unknown moons of Neptune. The planet also has two moons that were discovered earlier, giving it a total of eight.

Before the Voyager mission, ground-based scientists thought they had discovered partial rings, called ring arcs, around Neptune. The arcs turned out to be complete rings, although very irregular. The planet has at least five rings.

Triton, Neptune’s largest moon, is a little smaller than had been thought, measuring about 1,690 miles in diameter. It is also the coldest object ever seen in space, with a surface temperature of 400 degrees below zero. It has a surprising diversity of geological features, including ice volcanoes, and is one of the brightest objects in the solar system.

The evidence also suggests that Triton formed somewhere else, even farther out in the solar system than Neptune, and was captured by Neptune’s gravity as it passed by. It is probably very similar to Pluto, now the only planet in the solar system that has not been visited by a robotic spacecraft.