Voyager 2 passed within 5,000 kilometers (3,000 miles) of Neptune on August 25, 1989. Hours later, it passed 40,000 kilometers (25,000 miles) from Neptune's largest moon Triton, and then proceeded into the neighborhood beyond the outer planets.

The flyby generated a wealth of new data about the Neptune system. Voyager 2 discovered six small moons orbiting near Neptune's equatorial plane, bringing the planet's total number of known moons to eight. The spacecraft monitored Neptune's Great Dark Spot, a storm in which winds blow at up to 2,000 kilometers (1,200 miles) per hour, and also measured the planet's temperatures, radio waves, and magnetic field.

Voyager 2's observations of Triton revealed active geyser-like eruptions that spewed invisible nitrogen gas and dark dust particles several miles into the large moon's atmosphere. The craft also captured images of Neptune's rings, including details of the mysterious arcs, or clusters of dust, that form broken circles around the planet.

Today, Voyager 2 is about 8.8 billion kilometers (5.45 billion miles) from the sun, and is heading toward interstellar space at a speed of some 56,000 kilometers (35,000 miles) per hour. The project is now known as the Voyager Interstellar Mission.

Voyager 2 and its sister spacecraft Voyager 1 were both launched in the summer of 1977. Voyager 1 performed a flyby of Jupiter in 1979 and one of Saturn in 1980. Voyager 2 flew by Jupiter in 1979, Saturn in 1981, and Uranus in 1986, before conducting its Neptune flyby.