(News from NASA)
Voyager 2 is the only spacecraft ever to have flown past Neptune, and it left a lot of unanswered questions. The views were as stunning as they were puzzling, revealing massive, dark plumes of icy material spraying out from Triton‘s surface. But how? Images showed that the icy landscape was young and had been resurfaced over and over with fresh material. But what material, and from where? How could an ancient moon six times farther from the Sun than Jupiter still be active?
A new mission competing for selection under NASA’s Discovery Program aims to untangle these mysteries.
Called Trident—like the three-pronged spear carried by the Roman sea god Neptune—the team is one of four that is developing concept studies for new missions. Up to two will be selected by summer 2021 to become a full-fledged mission and, if Trident is selected, it would launch in October 2025 (with a backup in October 2026).
(Editor’s note: the other proposed missions are VERITAS to map Venus’ surface, DAVINCI+ to study Venus’ atmosphere, and the Io Volcanic Observer (IVO). All are fascinating and promise to deliver valuable data.)
The oddities of Triton could fill an almanac: As Neptune rotates, Triton orbits in the opposite direction. No other large moon in the solar system does that. And Triton’s orbit lies at an extreme tilt, offset from Neptune’s equator by 23 degrees. About three-quarters the diameter of our own Moon, Triton isn’t where it used to be, either. It likely migrated from the Kuiper Belt, a region beyond Neptune of icy bodies left over from the early solar system.
In addition Triton offers the largest unexplored solid surface in the solar system this side of the Kuiper Belt. Most of what we know of the moon came from Voyager 2 data, but we’ve only seen 40% of the moon’s surface. Trident would map most of the remainder.
“Triton is weird, but yet relevantly weird, because of the science we can do there. We know the surface has all these features we’ve never seen before, which motivates us to want to know ‘How does this world work?'”
– Karl Mitchell, Trident project scientist at JPL