Hi Board

I've been pondering planet formation in the light of a number of recent studies and some older ones.

The first - visit the physics pre-print archive and have a search - suggests that <1/3 of red dwarfs have Jovian planets, based on micro-lensing survey data.

The second [ http://astrobiology.arc.nasa.gov/palebluedot/abstracts/boss.html ] is just an abstract but it summarises current questions and doubts and black-spots in our understanding. Accretion seems to work fine for terrestrials, but there are problems with it for Jovians. Gravitational instabilities that become planets are the current buzz-idea, and we've all seen articles on them in the past couple of years.

I was also reading an old article by James Kasting [et al] on "habitable planets", and the thought is that liquid water environments should be fairly common [~ 50 % of planetary systems like ours], but that's ONLY for anoxic environments.

Kasting's conclusions will need modification because he forbade "cold starts" for planets locked in ice-ball states prior to their star warming up. Since the Earth now looks like one such planet I'd say cold starts are feasible.

The final article was from New Scientist [1992] and by David Hughes. In it he estimated about 1/24 stars can form planets - the rest either remain single stars with light disks or fragment into binaries due to overly heavy disks.

An interesting "prediction" was the formation of many jovians around lighter stars because more matter stayed in the disk. However the formation time [via accretion] goes up the further from stars you get - lower density and longer orbits. If we combine disk destruction and catastrophic gravitational interaction between the planets then that might explain the lack of jovians found via microlensing.

So maybe every star DOESN'T have planets?

Of course red dwarfs could form and hang on to terrestrials, but perhaps they get perturbed by the first two jovians that form and then undergo gravitational sling-shots?

As for statistics of current extra-solar planets they are slightly skewed by the fact that ONLY sun-like stars are being surveyed astrometrically. Since there are a lot of late K and early M stars that might have planets what are we missing???

Adam