On this day in 1989, 25 years ago, the Voyager 2 mission performed its flyby of Neptune. The probe’s final planetary encounter, Voyager passed within 3,000 miles of the planet’s north pole. During this time, definitive proof of Neptune’s rings were discovered, as well as close photographic observations of the “great dark spot.” This atmospheric disturbance has since disappeared based off of more recent observations by the Hubble Space Telescope, with the prevailing theory that it was merely a hole in the planet’s upper cloud layers.
Coincidentally, the New Horizons probe crosses Neptune’s orbit today on its way to Pluto. Unlike Voyager, however, New Horizons will not be able to fly by the planet. It is the final planetary milestone the mission passes on its way to a July, 2015 flyby of the planetoid.
Launched in 2006, New Horizons will mark a milestone in humanity’s exploration of the solar system. Once its flyby is complete, every major body in our solar system will have been visited by human machines. It is only the fifth probe ever launched on a trajectory out of the solar system.
For more information on Voyager’s flyby, click here.