📖 About Triton

Triton is Neptune’s largest moon and one of the most intriguing objects in the solar system. With a diameter of 2,707 km, it is the seventh-largest moon and the only large moon that orbits its planet in a retrograde direction—opposite to Neptune’s rotation. This strongly suggests Triton was originally a Kuiper Belt object captured by Neptune’s gravity billions of years ago.

Triton holds the record for the coldest measured surface in the solar system at -235°C (38 K). Despite this extreme cold, Voyager 2 discovered active nitrogen geysers erupting 8 km above the surface, driven by solar heating of subsurface nitrogen ice. The surface features a unique “cantaloupe terrain” of dimpled, melon-like patterns found nowhere else, along with vast frozen nitrogen plains and evidence of cryovolcanism.

Only one spacecraft has ever visited Triton—Voyager 2, which flew past on August 25, 1989, at a distance of just 40,000 km. This brief encounter revealed an unexpectedly complex and geologically young world. A proposed mission called Trident was studied by NASA to return to Triton, but was not selected. The planetary science community continues to advocate for a dedicated Neptune-Triton mission as a high priority.

🔭 Key Features

🔬 Science & Future

Triton provides a preview of what large Kuiper Belt objects like Pluto and Eris may look like up close. Its captured origin, active geology despite extreme cold, and potential subsurface ocean make it a compelling target for future exploration. Scientists believe tidal heating from Neptune may maintain liquid water beneath Triton’s icy crust.

A dedicated Neptune-Triton orbiter and probe mission has been identified as a high priority by the planetary science decadal survey. Such a mission would study Triton’s geology, geyser activity, and potential ocean, while also investigating Neptune’s atmosphere, rings, and magnetosphere. With current technology, a mission would take 12-16 years to reach the Neptune system.

📜 Discovery & Exploration

William Lassell discovered Triton on October 10, 1846—just 17 days after Neptune itself was found. Named after the Greek sea god and son of Poseidon (Neptune), Triton was the first Neptunian moon discovered. Its retrograde orbit was recognized as unusual from the earliest observations.

Voyager 2’s 1989 flyby remains our only close encounter with Triton. The spacecraft discovered active geysers, mapped the cantaloupe terrain, and measured the thin nitrogen atmosphere. Despite nearly 35 years since this visit, no follow-up mission has been launched, making a return to Triton one of the most anticipated goals in planetary exploration.