Triton & Outer-System Moons: Observation, Measurement & Evidence

Triton has a mostly icy surface with nitrogen, methane, and carbon monoxide frosts over a differentiated interior. Its retrograde orbit is highly unusual for a large moon. Other outer-system moons range from irregular captured bodies to round differentiated satellites shaped by tides, impacts, and volatile chemistry.

Voyager 2 imaged Triton's cantaloupe-like terrain, smooth plains, dark plume deposits, and a thin nitrogen atmosphere. Orbital direction and inclination support capture, and the absence of dense ancient cratering across parts of the surface indicates geological renewal.

A captured Triton would initially have occupied a more eccentric orbit, and tidal dissipation during orbital circularization could have generated substantial internal heat. Seasonal sunlight can drive nitrogen frost transport, while residual internal energy and volatile pressure may contribute to surface activity.

Voyager 2 imaging revealed smooth plains, cantaloupe terrain, young surfaces, and geyser-like plumes. Spectroscopy identifies volatile ices, while orbital dynamics make in-place formation difficult. Crater counts suggest extensive resurfacing compared with many small outer moons.