Hi Guys

Been reading about forming exoplanets via Prof. Michael Woolfson's Capture theory. The basics of the Capture theory are quite simple - planets form via gravitational instability. To produce a disc in which this can happen the proto-Sun interacted with another protostar in their common birth nebula and captured material from it. The Sun and planets formed close in time from the same material, but without the usual complications of momentum transfer between the two in the Nebula Model.

The capture of the disk set up instabilities that collapsed into six planets (with some smaller moons forming within the mix) - two of these destructively interacted [collided] to form Venus and Earth from their solid debris.

Recently George Wetherill and others have published work that concurs that gravitational instability is how the Jovians & ice-giants probably formed...

http://au.arxiv.org/abs/astro-ph/0112406

Other work suggests that accretion really isn't an option for the ice-giants where they are and they either migrated or formed by some other means. Perhaps Jupiter set up disk instabilities that spawned the other giants?

I think the (possible) observations of free-floating semi-planets in various birth nebula indicates a lot of interaction between protostars and hence the general plausibility of the Capture theory is increased. It's worth further work as Woolfson and colleagues plead.

According to Woolfson and co-workers the number of stars with planet systems is between 1% and 14% depending on the birth nebula...

S202.061
Modelling planet formation by

Capture-theory interactions
M.M.~Woolfson et al.

Physics Department, University of York, U.K.

The embedded stage of the evolution of a stellar cluster has star number densities in the range 10^{4} to 10^{5}/ pc^{-3}. There will be similar number densities of bodies with sub-main-sequence mass, including brown dwarfs. Lower mass bodies, forming later and in a diffuse state, will frequently interact with higher mass condensed stars within the Roche limit. Such interactions have been simulated using smoothed particle hydrodynamics, incorporating a novel and realistic modelling of radiation transfer, applicable over all opacities and optical depths (S.~Oxley 1999, Modelling the Capture Theory for the Origin of Planetary Systems, D.Phil. thesis, University of York, www.droxley.freeserve.co.uk). The diffuse bodies are completely disrupted, forming planetary-mass condensations, some of which are captured by the primary body. Planetary systems with one or more planets are produced in this way. Depending on the parameters of the embedded stage, between 1 and 14% of higher-mass stars are estimated to have planetary companions. Co-authors: S.~Oxley

END QUOTE

[Adam] At the web-site quoted is Oxley's PhD thesis which was rejected for publication, revised and rejected etc... by referees to the Monthly Notices of the Royal Astronomical Society. Some of the referees made contructive comments that the authors took on-board [hence they aren't cranks] but some showed the kind of know-it-all closed-mindedness that cranks have equally. Seems established opinion can be as jealous a meme as radical opinion.

Woolfson and Oxley reply at...

http://www-users.york.ac.uk/~mmw1/

Implications...

Planetary systems may be rarer than we think. If Earth and Venus are collisional remnants then our system might be a chancier event than normally believed - though that might be a conclusion drawn too soon. From what I have seen so far there is a lot of interaction in planet systems - perhaps the breakdown is 1/3 stabilised orbits, 1/3 ejections and 1/3 collisions???

As the exoplanets are telling us planetary interactions are more complicated and significant than anyone imagined working on the Disc/Nebula model. But the Capture theory begins with interactions and high-eccentricities.

I think we will have to wait and see, but the more I see the less sure I become that we have all the options before us yet.

Adam