Reassessing the origin of Triton

Abstract

Agnor & Hamilton (2006) demonstrated that the disruption of a binary was an effective mechanism to capture Triton. The subsequent evolution of Triton's post-capture orbit could have proceeded through gravitational tides. The study by Agnor & Hamilton (2006) is repeated in the framework of the Nice model to determine the post-capture orbit of Triton. After capture it is then subjected to tidal evolution. The perturbations from the Sun and the figure of Neptune are included. The perturbations from the Sun acting on Triton cause it to spend a long time in its high-eccentricity phase, usually of the order of 10 Myr, while the typical time to circularise to its current orbit is some 200 Myr. The current orbit of Triton is consistent with an origin through binary capture and tidal evolution, even though the model prefers Triton to be closer to Neptune than it is today. The probability of capturing Triton in this manner is approximately 0.7%. Since the capture of Triton was at most a 50% event -- since only Neptune has one, but Uranus does not -- we deduce that in the primordial trans-Neptunian disc there were 100 binaries with at least one Triton-sized member. Morbidelli et al. (2009) concludes there were some 1000 Triton-sized bodies in the trans-Neptunian proto-planetary disc, so the primordial binary fraction with at least one Triton-sized member is 10%. This value is consistent with theoretical predictions, but at the low end. If Triton was captured at the same time as Neptune's irregular satellites, the far majority of these, including Nereid, would be lost. This suggests either that Triton was captured on an orbit with a small semi-major axis a < 50 R_N (a rare event), or that it was captured before the dynamical instability of the Nice model, or that some other mechanism was at play. The issue of keeping the irregular satellites remains unresolved.

Accepted in Icarus 2011

References in corpus (11)

• Origin of the Structure of the Kuiper Belt during a Dynamical Instability in the Orbits of Uranus and Neptune
• The Size Distribution of Trans-Neptunian Bodies
• Dynamics of the giant planets of the solar system in the gaseous proto-planetary disk and relationship to the current orbital architecture
• The Physics of Bodily Tides in Terrestrial Planets, and the Appropriate Scales of Dynamical Evolution
• Circumplanetary disc properties obtained from radiation hydrodynamical simulations of gas accretion by protoplanets
• Satellites of the largest Kuiper belt objects
• Destruction of Binary Minor Planets During Neptune Scattering
• Secular evolution of a satellite by tidal effect. Application to Triton
• Constraints on the Orbital Evolution of Triton
• The Short Rotation Period of Nereid
• On the Detection of Two New Transneptunian Binaries from the CFEPS Kuiper Belt Survey

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• Triton's Evolution with a Primordial Neptunian Satellite System
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• Volatile transport modeling on Triton with new observational constraints
• Astrometry of the main satellites of Uranus: 18 years of observations
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• Forming Massive Terrestrial Satellites through Binary-Exchange Capture
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• Nereid as a Regular Satellite of Neptune
• New Moons of Uranus and Neptune from Ultra-Deep Pencil Beam Surveys