Capture of Triton
Triton's capture explains its retrograde, highly inclined orbit.
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The capture of Triton refers to the hypothesized event in which Neptune's largest moon, Triton, was captured from a heliocentric orbit early in the Solar System's history. This capture is notable because Triton is the only known large moon with a retrograde, highly inclined orbit, conflicting with the conventional theory that large moons form from debris discs and orbit prograde. The capture would have been a cataclysmic event, severely disrupting any pre-existing moons around Neptune and reducing them to rubble.
Quick Facts
- First proposed by
- Raymond A. Lyttleton
- Year of first proposal
- 1936
- Alternative model proposed by
- Paolo Farinella (1979)
- Encounter model proposed by
- Robert S. Harrington and Tom Van Flandern (1979)
Facts from the source article.
Background
Early attempts to explain Triton's orbit included a 1936 hypothesis by British astronomer Raymond A. Lyttleton, who postulated that both Triton and Pluto were once large regular moons of Neptune, with mutual interactions ejecting Pluto and flipping Triton's orbit. This hypothesis was based on overestimated masses; as true masses were determined, it was recognized that Pluto could not reverse Triton's orbit. In 1979, Paolo Farinella proposed a hybrid model where only Pluto was an indigenous satellite and Triton was captured.
That same year, Robert S. Harrington and Tom Van Flandern proposed an encounter with a rogue object several times more massive than Earth, but this was contested in 1980 by Farinella and collaborators, who noted it failed to explain why Neptune's orbit was not disrupted. By the 1980s, capture models gained acceptance, and in 1984 William B. McKinnon refuted catastrophic Pluto-Triton interactions, proposing both worlds as leftover icy planetesimals with Triton later captured.
After Voyager 2's flyby, precise measurements of Triton's diameter and mass allowed detailed modeling of its capture, including work by McKinnon and Lance A. M. Benner in 1990.
Frequently Asked Questions
Who first proposed that Triton was captured?
Raymond A. Lyttleton introduced the concept in 1936. Since then, researchers including Paolo Farinella, Robert S. Harrington, Tom Van Flandern, and the pair Craig B. Agnor and Douglas P. Hamilton have each offered their own versions of how the capture might have mechanically unfolded.
What happened to Neptune's other moons during the capture event?
The violent gravitational encounter would have torn apart any moons already circling Neptune at the time, shredding them into a cloud of rubble. The planet's current faint ring system and tiny inner satellites may be surviving fragments of that destruction.
How do scientists think the capture mechanism actually worked?
The most widely discussed picture is a three-body interaction, refined by Agnor and Hamilton in 2006, in which a passing body helps shed just enough orbital energy for Triton to become bound to Neptune. Earlier 1979 proposals by Farinella, and separately by Harrington and Van Flandern, explored different encounter geometries aimed at the same outcome.
More in Moons of Neptune
Elsewhere in Moons of Uranus and Neptune
Sources
Compiled from Wikipedia and the sources listed below. Text from Wikipedia is available under CC BY-SA 4.0; this entry is adapted from it.
- Wikipedia: Capture of Triton (CC BY-SA 4.0).
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