And now, pending approval, we might soon get our best glimpse yet. NASA's Jet Propulsion Laboratory proposed on Tuesday at a conference in Texas to send a spacecraft called "Trident" to Triton - with the goal of sussing out whether it's a habitable world.
Rather than spending billions of dollars, the proposed spacecraft called Trident aims to keep costs low - roughly the "price of a small mission to the moon," in the New York Times' reckoning.
"The time is now to do it at a low cost," said Louise Prockter at Tuesday's Lunar and Planetary Science Conference in Texas, director of the Lunar and Planetary Institute in Houston and the principal investigator of the proposed mission.
"And we will investigate whether it is a habitable world, which is of huge importance."
Along with a Triton flyby, Trident is competing against proposals for a visit to Jupiter's moon Io and a return to Venus - it's been almost twenty years since NASA's Cassini-Huygens spacecraft visited the second planet from the Sun.
The last good look we got of Neptune was during a 1989 flyby of NASA's Voyager 2 - the first time any spacecraft had ever done so.
"We are comparing with the Voyager encounter in 1989, which was built on early 1970s technology, essentially a television camera attached to a fax machine," said Karl Mitchell, the proposed mission's project scientist, as quoted by the Times.
Editor's Note 10 April 2019: The original Futurism story said Trident would also be visiting Jupiter's moon Io and Venus. These are on the spacecraft's route, but it will compete against other mission proposals for these tasks. The story has been updated by the ScienceAlert team.