What did Voyager 2 discover on Neptune's moon Triton?

Voyager 2 discovered nitrogen geysers, or geyser-like plumes, erupting on Neptune’s moon Triton. During its 1989 flyby, the spacecraft photographed dark columns rising from Triton’s surface and leaving streaks of material across the icy landscape.

At least four active eruptions were identified in the Voyager images, with the best-documented plumes reaching roughly 8 kilometres high and drifting more than 100 kilometres downwind. The plumes were not ordinary water geysers like those later observed on Saturn’s moon Enceladus. They were driven by nitrogen near Triton’s extremely cold surface.

A leading explanation is that sunlight warmed translucent nitrogen ice, creating a subsurface greenhouse effect. Pressurized nitrogen gas then burst through the surface, carrying dark dust or particles into the thin atmosphere. Triton’s surface temperature is near 38 kelvins, yet this seasonal solar heating can still drive striking geological activity. The discovery showed that even a distant icy moon could be active.