DDA 36th Meeting, 10-14 April 2005
Session 11 Orbits and Orbit Evolution II: Moons
Oral, Wednesday, April 13, 2005, 9:35am-12:15pm

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[11.03] Constraints on the Orbital Evolution of Triton

M. Cuk, B. J. Gladman (Univ. of British Columbia)

In order to study the early post-capture history of Triton, we have modified a symplectic integrator to include eccentricity tides and drag from a debris disk. Our simulations of Triton's post-capture orbit confirm the importance of Kozai-type oscillations in its orbital elements (Benner and McKinnon 1994). In the context of the model of Goldreich et al. (1989), these variations require average pericenter distances to be much higher than the 7 Neptune radii they used. Due to the sensitive dependence of tidal dissipation on the pericenter distance, the real timescale for the tidal orbital evolution of Triton becomes longer than the age of the Solar System.

Extant irregular satellites (Holman et al. 2004) present a new constraint on Triton's orbital history. Our integrations of large numbers of test particles require a timescale for Triton's orbital evolution to be less than 105 yrs for any distant irregular satellies to survive Triton's passage. This timescale is wildly inconsistent with the model of Goldreich et al. (time scale of >108 yrs), but consistent with gas-drag model of McKinnon and Leith (1994) which requires the presence of a primordial nebula. We suggest another source of drag that is available regardless of the capture epoch: debris from satellite-satellite collisions. Putative major satellites are very likely to collide among themselves on short timescales after being perturbed by Triton (cf. Banfield and Murray 1992). This subsequent collisional debris disk would be prevented from re-accreting by Triton's perturbations and would eventually be swept up by Triton. Given that the total mass of Uranian system is 40% of that of Triton, large scale evolution is possible due to passages through such a disk.The orbital evolution we describe here could have followed either collisional or the recently-discussed three-body-interaction-based capture (Agnor and Hamilton 2004).

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Bulletin of the American Astronomical Society, 37 #2
© 2005. The American Astronomical Soceity.