Triton is the largest of Neptune's 13 moons

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Triton
Paul Scott Anderson in SPACE | March 28, 2019

Triton is Neptune’s largest moon. It’s a bizarre and geologically active world – a possible ocean moon – visited by Voyager 2 in 1989. Now, NASA has proposed a new mission called Trident to sweep past Triton again in 2038.

Neptune’s largest moon Triton as seen by Voyager 2 during its flyby in 1989. The south polar cap – with its nitrogen geysers – is in the bottom portion of this image and Triton’s famous “cantaloupe terrain” is at the top. Image via NASA/JPL/USGS.

Over the past few decades, robotic missions to the outer solar system have shown that water worlds seem to be quite common. We’ve seen multiple moons with an icy surface crust and, scientists believe, a liquid water ocean below. Jupiter’s moon Europa and Saturn’s moons Enceladus and Titan are among the most intriguing of these water moons. Even Pluto might have a subsurface ocean and evidence suggests that the dwarf planet Ceres had one as well, in the past.

But there’s another compelling world that hasn’t been visited again yet for decades – and should be – according to NASA. That is Neptune’s largest moon Triton. On March 19, 2019, at the Lunar and Planetary Science Conference 2019 (LPSC 50), NASA announced a proposed flyby mission called Trident to investigate whether Triton does, as suspected, have a subsurface ocean, an ocean with the potential for habitability.

The flyby, similar to the New Horizons flyby of Pluto in 2015, would occur in 2038. The proposal is outlined in two papers.

The mission, if approved, would be part of NASA’s Discovery Program, which supports lower-cost missions for under $500 million. Those missions are launched every two years, with the InSight lander on Mars being the most recent.