From: ben (benboc@lineone.net)
Date: Sat Oct 15 2005 - 16:58:01 MDT
I think the point is that more recently formed stars have higher
metallicity. In past generations of stars, metallicity was lower. The
first generation of stars would have had almost zero metallicity.
BTW, Millions of years is the wrong timescale for stars. Except maybe
really, really massive ones.
You probably need several (at least two, maybe three) generations of
stars to get enough heavy elements to make rocky planets, so more
recently-formed stars will have a better chance of hosting life (as we
know it. Gregory Benford seems keen on the idea of lifeforms based on
magnetic fields and plasma, but that's a whole different story, and i
don't know whether he regards that as a real possibility or just a good
story line).
So, no, younger stars have not always been more likely to have planets.
Just more recent ones. Our sun is likely to be a third-generation star,
AFAIK.
The very first stars could only have had gas planets, if any (i wonder
if they might have had lithium cores??).
ben
Tennessee Leeuwenburg wrote:
> Great observation, but there is one further subtlety.
>
> Have younger stars *always* been more likely to have planets around
> them? For example, a million years ago, would there have actually been
> fewer planets?
>
> Obviously, a million (/billion/whatever) years ago, all the stars would
> have been correspondingly younger. Assuming the same distributions we
> see today, there would have been just as many young stars, ergo just as
> many planets.
>
> Either older stars once had planets, and they have since disappeared
> through cosmic misadventure, or perhaps planets *per se* are a
> relatively new phenomenon.
>
> Which is it?
>
> Cheers,
> -T
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