Comments on: The sand reckoner

By: greg

greg — Wed, 12 Jul 2006 18:04:34 +0000

Hi Andy,

Thanks for your question as well!

The carbon-rich dust and debris orbiting Beta Pic might be more indicative of chemical processing in the ices of the outer regions of Beta Pic’s protoplanetary disk. It is true, however, that carbon will be an important core-forming element, and that a carbon-rich nebula might have an advantage in Jovian planet formation. We’ve been interested in the role of silicon as a proxy for oxygen (see the upcoming posts) but as the number of planets and surveyed stars increases, it would be interesting to do a statistical analysis of planet occurence as a function of carbon abundance of the parent star. That is, the effect is probably there, but its probably subtle.

I’d rather sweep the PSR 1620-26 planet under the rug :). In all seriousness, though, there’s no way that planet formed via core accretion, so it must be the result of gravitational instability. I better go and look at the papers on that planet, and I’ll check back later if I can think of anything interesting to say about it. (I didn’t pay much attention to it when it was announced.)

best,
Greg

By: greg

greg — Wed, 12 Jul 2006 17:53:24 +0000

Hi Vincent,

Thanks for your question. Terrestrial planet formation should not be adversely affected until the metallicity gets really low. Stars in our Galaxy’s globular clusters, for example, often have only about 1% of the Sun’s metal content, and I would expect that the terrestrial planets around these stars are pretty low mass. For stars of, say, half solar metallicity, however, there should be plenty of habitable terrestrial planets.

And you’re right as well about the high-metallicity systems as well. When you have off-the-hook planet formation, the migration of the Jovian-mass planets through the terrestrial region is going to likely clear things out and make the formation of habitable worlds less likely.

best,
Greg

By: systemic - Pollux

systemic - Pollux — Wed, 12 Jul 2006 17:47:13 +0000

[...] In last Saturday’s post, I wrote about predictions of the core-accretion hypothesis with respect to planet formation. The ability to quickly build a Jovian-mass planet depends on the surface density of solid material in the protostellar disk. A lot of solids leads to rapid buildup of cores, and hence the ability of planets to achieve rapid gas accretion before the protostellar disk dissipates. (The spiral wave-induced evolution of marginally gravitationally stable disks leads one to expect that disk masses will correlate with the masses of the central stars, see this paper for a lot more discussion.) All other factors being equal, one expects that Jupiter-mass planets will be rarer around stars that have significantly less mass than the Sun, and that conversely, Jupiter-mass planets will be more common around planets of somewhat higher mass than the Sun. (Note that for really massive stars, the luminosity of the star itself will rapidly photo-evaporate the disk, which will cause problems for giant planet formation via core accretion). [...]

By: andy

andy — Sat, 08 Jul 2006 21:22:53 +0000

Would carbon-rich discs like the one(s) around Beta Pictoris promote or inhibit gas giant formation?

Also, what’s the thinking on forming the planet of PSR 1620-26 in a low-metallicity environment?

By: Vincent

Vincent — Sat, 08 Jul 2006 20:43:51 +0000

Hi all ! :-D
Thanks for this post, Greg ;-) .
With this model, the stellar metallicity seems to have an influence on the forming of planets.

You said : “Stars with subsolar metallicity will rarely be accompanied by Jupiter-mass planets.”

My question : Could the forming of low-mass terrestrial planets(like Earth, Mars etc…) be conditioned by the stellar metallicity ?
From time to time, I say to myself that stars with a high metallicity would not be good candidates to look (in the future) terrestrial planets…
For example, 55 Cancri may have only jovian and neptunian planets !

What do you think about it?

Thanks.