How did tidal interactions change Triton’s original orbit?

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Moons of Neptune: Triton — Triton Image of Triton, Neptune's largest satellite, captured by a camera aboard Voyager 2, 1989.

Tidal interactions played a critical role in the evolution of Triton’s orbit following its capture by Neptune. Initially, Triton was placed into an elongated, highly inclined, and retrograde orbit.

Over time, tidal interactions—cyclic deformations caused by the gravitational attraction between the two bodies—selectively retarded Triton's motion during the closer portions of its orbit. This process gradually circularized its path around the planet. It is estimated that this transition from capture to a circular orbit may have spanned more than one billion years. During this period, the intense tidal forces likely melted Triton's entire interior, leading to internal differentiation where denser materials sank to form a core while more volatile materials rose to the surface.1