Neptune's Unanswered Questions To date, there has been only one mission to Neptune, the Voyager 2 flyby of 1989. That flyby capped a "grand tour" of the outer planets that took advantage of a unique gravitational alignment to slingshot the spacecraft from Jupiter to Saturn to Uranus to Neptune. While there is no mission to Neptune currently funded, a Uranus orbiter and probe proposed in the Planetary Decadal Survey of 2013-2022 could be adapted to explore Neptune if the current alignment of Jupiter were more favorable, Amy Simon, a senior scientist for planetary atmospheres at the NASA Goddard Space Flight Center, told Space.com. Until another spacecraft can get out there, scientists must rely on ground-based telescopes such as Keck II, and space-based observatories such as the Hubble Space Telescope and the Kepler space telescope, to get occasional glimpses of Neptune in between their other duties. This leaves a lot of unanswered questions about the blue planet. Here are some of the