Year: 1989

NASA announces the confirmation of what are believed to be partial rings around planet Neptune, as discovered in images taken by the unmanned Voyager 2 space probe. The ring arcs are found in close proximity to several new satellites, also spotted in Voyager 2 images, which are too small to have been seen form Earth-based telescopes. Ground-based telescopes had led scientists to believe that they would find partial rings, or complete dark rings, at Neptune; at this time, however, and at a distance of 13 million miles, what the project scientists don’t expect is that the rings will be revealed to completely encircle the planet within mere weeks.

The unmanned space probe Voyager 2, almost exactly 12 years after leaving Earth, visits its last planet in the solar system, Neptune. Since mission planners have no further targets for Voyager, they have a free hand in picking its final destinations. An extremely close trajectory over Neptune’s north pole, bringing Voyager 2 within 18,000 miles of the cloudtops of the solar system’s windiest planet, deflects Voyager downward behind Neptune for a close look at its large moon, Triton. Six new moons are discovered, and the “ring arcs” that astronomers have theorized for years turn out to be complete rings made of extremely dark material. After the surprisingly featureless face of Uranus, Neptune proves to be unexpectedly active, with a large dark storm dominating its atmosphere.

As scientists marvel over the latest data and pictures from Voyager 2 as it leaves Neptune, images of the planet’s large moon Triton prove to be jaw-dropping. Active geysers blast dark material – possibly evidence of cryovolcanism – over the moon’s mottled surface, and an atmosphere is measured. Virtually no craters caused by meteor impacts are spotted, meaning that Triton’s surface is geologically active – all completely new discoveries to Earth-based scientists. Perhaps the most frustrating part of all of the new information is that no further missions to Neptune are in serious consideration by NASA to follow up on Voyager 2’s discoveries.

NASA’s unmanned Voyager 2 space probe leaves the vicinity of the planet Neptune, the outermost planet to have been explored by a man-made spacecraft. (At this point in time, Pluto is still considered a planet – the only one to which NASA hasn’t sent a space probe – though by the time a vehicle is dispatched to Pluto in the 21st century, Pluto has been demoted to “minor planet” status.) Though not expected to function beyond 2025 due to the slow decay of its nuclear power source, Voyager 2 may survive long enough to pass within 25,000,000,000,000 miles of Sirius in a quarter of a million years.