Britannica
Sources used in this answer
What does it mean that Triton has a retrograde orbit?
Created from Britannica articles
using AI.
AI can make mistakes, so verify using Britannica articles.
Triton
Image of Triton, Neptune's largest satellite, captured by a camera aboard Voyager 2, 1989.
Triton’s retrograde orbit means that it revolves around Neptune in a direction opposite to the planet’s own rotation.12
This characteristic is highly unusual for a large moon in our solar system. Astronomers believe this unique orbital motion, combined with the moon's high orbital inclination, indicates that Triton did not form alongside Neptune. Instead, it is thought to be a captured object—likely an icy planetesimal that originally formed independently in the outer solar system, similar to the dwarf planet Pluto.12
Following its capture, tidal interactions between Triton and Neptune gradually reshaped its path from a highly eccentric, captured orbit into the circular one observed today.12