Triton

Triton is Neptune’s largest moon and the seventh-largest moon in the solar system. It is unique among large moons because it orbits Neptune in the opposite direction of the planet’s rotation—a retrograde orbit.

A Captured World

Scientists believe Triton was not formed alongside Neptune, but was instead captured by the planet’s gravity from the Kuiper Belt. This capture may have occurred relatively recently in astronomical terms, about 4.5 billion years ago.

Cryovolcanoes and Geysers

Triton has active cryovolcanoes—volcanoes that erupt not molten rock, but liquid nitrogen, methane, and ammonia. These cryovolcanoes create towering plumes that can reach heights of up to 8 kilometers.

The moon’s surface is extremely cold, with temperatures around -235°C (-391°F), making it one of the coldest places in the solar system. Despite this, Triton shows evidence of recent geological activity.

Thin Atmosphere and Surface Features

Triton has a thin atmosphere composed mostly of nitrogen with small amounts of methane. This atmosphere is so thin that surface pressure is about 14,000 times less than Earth’s.

The surface features include smooth plains, ridges, and valleys. Some areas show evidence of recent resurfacing, possibly from cryovolcanic activity or the eruption of nitrogen geysers.

Exploration

Triton was visited by Voyager 2 in 1989, providing the only close-up images we have of this distant moon. Future missions to study Triton more closely are being considered, as it represents a unique opportunity to study an ice moon with active geology.

Triton’s retrograde orbit and youthful surface make it one of the most intriguing objects in the outer solar system.