Capture of Triton

Triton, the largest moon of the ice giant planet Neptune, is hypothesized to have been captured from heliocentric orbit.

To address this, in 1979 a team of astronomers led by P. Farinella proposed a "hybrid" model, where only Pluto was an indigenous satellite of Neptune and Triton is a captured object.

[2]: 419–420  Alternatively, astronomers R. S. Harrington and T. C. van Flandern proposed that same year that an encounter with a rogue object several times more massive than Earth could provide the gravitational influence and energy necessary to eject Pluto and reverse Triton's orbit whilst disrupting the rest of the Neptune system.

[5]: 1749 Models invoking catastrophic interactions between Pluto and Triton were refuted by W. B. McKinnon in 1984, demonstrating that such a scenario was impossible given the energies required, regardless of configuration.

Instead, McKinnon proposed that both worlds are leftover icy planetesimals from the early Solar System, with Triton being later captured into Neptune's orbit.

Early post-flyby research includes modelling by W. B. McKinnon and L. A. M. Benner in 1990, who sought to relate Triton's expected thermal evolution following its capture to the geological characteristics observed by Voyager 2.

[10] Three-body capture, more recently proposed by C. B. Agnor and D. P. Hamilton in 2006, involves Triton in a binary system with a third object, similar to Pluto and its large moon Charon.

The event would have been "gentle and brief", as Triton is not subject to violent disruption or potentially dangerous post-capture orbital decay.

As a result, Triton's high eccentricity phase would have greatly perturbed any other irregular moons present at the time of its capture, including Nereid.

The amount of energy dissipated was likely enough to contribute to Triton's differentiation into a rocky core and icy mantle, potentially to the point of melting the satellite entirely.

[18] Scenarios involving a close encounter between Neptune and a perturbing planet, similar to the model by Harrington and van Flandern, have been proposed.

Using numerical simulations, the authors found that the likelihood of Triton achieving a retrograde orbit depends heavily on the axial tilt of Neptune after the first collision.