What factors contribute to the migration of hot Jupiters?

[marcus]

they ran computer simulations of 8500 planetary systems to see how giant planets could sometimes MIGRATE in close to the star

and they got some statistics of what one might expect.

I cannot vouch for this paper, or say how it stacks up compared with other similar papers, but this business of hot Jupiters is a great puzzle so I figure anything along these lines that might give some answers could be interesting.

the paper has been accepted for publication in a peer-review journal so that is one good sign at least. if someone checks it out please let us know how good a paper and if it does help answer why there are so many giant planets are in close to their stars (like as close as Mercury, or closer)

http://arxiv.org/abs/astro-ph/0505234
Giant Planet Migration through the Action of Disk Torques and Planet Scattering
Althea V. Moorhead, Fred C. Adams
46 pages including 15 figures; accepted to ICARUS

"This paper presents a parametric study of giant planet migration through the combined action of disk torques and planet-planet scattering. The torques exerted on planets during Type II migration in circumstellar disks readily decrease the semi-major axes, whereas scattering between planets increases the orbital eccentricities. This paper presents a parametric exploration of the possible parameter space for this migration scenario using two (initial) planetary mass distributions and a range of values for the time scale of eccentricity damping (due to the disk). For each class of systems, many realizations of the simulations are performed in order to determine the distributions of the resulting orbital elements of the surviving planets; this paper presents the results of 8500 numerical experiments. Our goal is to study the physics of this particular migration mechanism and to test it against observations of extrasolar planets. The action of disk torques and planet-planet scattering results in a distribution of final orbital elements that fills the a-e plane, in rough agreement with the orbital elements of observed extrasolar planets. In addition to specifying the orbital elements, we characterize this migration mechanism by finding the percentages of ejected and accreted planets, the number of collisions, the dependence of outcomes on planetary masses, the time spent in 2:1 and 3:1 resonances, and the effects of the planetary IMF. We also determine the distribution of inclination angles of surviving planets and the distribution of ejection speeds for exiled planets."

 

[marcus]

"5. Conclusion

This paper explores a migration scenario in which multiple giant planets are driven inward through the action of tidal torques in a circumstellar disk. In this case, the outer planet interacts with the disk, which drains energy and angular momentum away from the planetary orbit. As the outer planet migrates inward, it eventually becomes close enough to the interior planet to force it inward and to drive eccentricity growth with increasingly violent interactions. Such systems are generally not stable in the long term and adjust themselves to stability by ejecting a planet, accreting a planet onto the central star, or by having the two planets collide. The surviving planet is left on an eccentric orbit of varying semi-major axis, roughly consistent with the orbits of observed extrasolar planets. On longer time scales, tidal interactions with the central star act to circularize the orbits of the closet planets. We have presented a comprehensive, but not exhaustive, exploration of parameter space for this migration scenario. Our main results can be summarized as follows: [1] This migration scenario results in a wide variety of final systems with a broad distribution of orbital elements. In particular, this migration scenario can fill essentially the entire a-e plane for semi-major axes a smaller than the initial values. The observed extrasolar planets have orbital elements that fill the a-e plane in roughly the same way (see Figs. 9 – 15). When the theoretical ensemble of planets is corrected for additional orbital evolution due to interactions with the circumstellar disk (on approx. 1 Myr time scales) and tidal interactions with the central star (on approx. 1 Gyr time scales), the resulting distributions of theoretical orbital elements are in reasonable agreement with those of the observed sample of extrasolar planets..."

"...This migration scenario produces a full distribution of orbital elements for the surviving planets and is in reasonable agreement with observations. In order for this mechanism to be successful, the systems must have a number of properties, and it is useful to summarize them here: The planets that end up in the currently observed region of the a-e plane are assumed to have formed in disk annulus r = 3 - 7 AU, roughly where Jupiter lives in our solar system..."

 

[Chronos]

It looks like a very good paper to me, marcus. The initial assumptions are few [a big plus in my book] and the results do not appear to suffer from over-analysis.