phil wrote:

Great conference! Geoff Marcy announced 6 more new exoplanets, some with multi-year periods. I asked him what he thought of the prevalance of elliptical orbit Jovians vis-a-vis our circular solar system. He said he figured around 10% of systems had reasonably circular orbits. He thinks the reason the others are elliptical is that typically LOTS of big planets form and subsequently the several superJovians gravitationally interact and modify their orbits, ejecting some, sending some sunward, etc. Interesting.

my comment:
Sounds like Marcy favours the disk instability model for Jovian formation - since it typically fragments disks into lots of gas-planets, which can then interact all over the place. Alan Boss is the chief investigator of this scenario and has had some successes ( and failures) in simulations of solar nebulae.

Alternatively the Capture Model, developed by John Dormand and Michael Woolfson typically produces Jovians on highly elliptical orbits that seriously interact before the system settles into a stable configuration - pole-tilts and planetary collisions have a moderately high probability of occurring in such a scenario, typically ~ 25%. For example, Earth-Venus might be the accreted remnants of the core of a gas-giant that was ruptured by another that was itself thrown into interstellar space. The Capture Theory - unlike most theories - naturally produces a lot of sub-stellar masses on hyperbolic trajectories that throw them free of any particular star. This explains neatly all the free-floater "planets" seen in very young nebula.

Adam