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Voyager 2 at Neptune

August 25, 2014

The solar system’s most distant planet has received only one emissary from Earth. Voyager 2 flew by Neptune 25 years ago today, completing its tour of the four giant planets. It photographed clouds in Neptune’s blue atmosphere and geysers on its biggest moon.

Neptune is the fourth-largest planet — almost four times the diameter of Earth. But it’s almost three billion miles away, so until Voyager’s encounter it was poorly known. All astronomers could see was a tiny blue disk — the color of methane in its upper atmosphere — orbited by two even tinier moons.

But on August 25th, 1989, Voyager 2 passed just 3,000 miles above Neptune’s clouds. Its cameras saw a large dark oval, which was named the Great Dark Spot. It was either a storm in the planet’s upper atmosphere, or a hole in the top layer of clouds that offered a view of deeper layers.

Voyager then skimmed past Triton, the planet’s largest moon. It saw a mottled surface that resembled the skin of a cantaloupe. It also saw dark geysers shooting many miles high. The geysers consisted of dark particles of ice that fell onto the surface, forming dark streaks.

Voyager also discovered dark rings around the giant planet, plus six small moons; more about that tomorrow.

After Neptune, Voyager 2 headed out of the solar system. It recently exited the magnetic “bubble” that marks the solar system’s edge. It continues to operate today, providing our first glimpse of interstellar space.

Script by Damond Benningfield, Copyright 2014

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