Nearly 33 years have passed since the first and only close flyby of Neptune by a spacecraft, performed by NASA’s Voyager 2. Nothing has returned to Neptune since it did on August 25, 1989, marking the end of the Voyager mission’s Grand Tour of the solar system’s four big planets—Jupiter, Saturn, Uranus, and Neptune. Voyager 2, in the meantime, has gotten into interstellar space.
What Neptune-related studies are there? And why do experts believe it’s time to travel back?