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Notes and resources

Current draft: Capture of Triton

Triton, the largest moon of the ice giant Neptune, is hypothesized to have been captured from heliocentric orbit. This is unique amongst all known large moons of the Solar System, which are all thought to have formed from a disc of dust and debris surrounding their parent planets.

History

Early attempts to explain Triton's unusual orbit include a hypothesis first proposed by astronomer R. A. Lyttleton in 1936, proposing that both Triton and Pluto were once large regular moons of Neptune. Mutual interactions between the two would then eject Pluto and flip Triton's orbit, explaining the former's then-apparent isolation and the latter's retrograde orbit. ^[1] However, the original hypothesis was borne out of heavily overestimated masses for both Pluto and Triton; as estimates for their masses approached their true values, it was recognized that Pluto could not realistically reverse Triton's 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. ^[3] This "encounter" model was contested by P. Farinella and collaborators in 1980, who noted that it failed to explain why Neptune's orbit was not disrupted despite encountering such a massive object. Thus, into the 1980's capture models began to grow more accepted, ^[4] and by 1989 several researchers had explored Triton's orbital and thermal history under a capture scenario. ^[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 Triton and Pluto are leftover icy planetesimals from the early Solar System, with Triton being later captured into Neptune orbit. ^{[6] [7]: L23} Following the Voyager 2 spacecraft's flyby of the Neptune system, Triton's physical parameters—including its diameter and mass—were measured with precision for the first time, ^[8]: 1437 thereby allowing researchers to investigate and model Triton's putative capture in greater detail. 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. ^[9]

Initial capture

Capture mechanisms

Subsequent effects

Tidal heating

Disruption of primordial moons

Eventual destruction

Alternatives to capture

See also

References