Just listened to AstronomyCast on Globular Clusters and enjoyed it so much! Fasinating stuff. I will never forget Charles Bonestell's painting of a planet just outside such a cluster. And Mr. Cain's speculations about a planet got me to thinking. (watch out!).

I realize that globular clusters are poor in metals (mm, are we talking real metals or those astrophysical metals - i.e. anything heavier than helium?) and probably did not have as much planet formation as say our local stellar neighbor but with the passage of time and the demise of the larger members, I wonder if earth-like planets have a chance to form from supernova remnants? What is the likelihood a planet like that would be captured and have a stable orbit in the cluster? What is the likelihood if it being in the "habitable" zone of a cluster member, as compared to stars on the disc of the Milky War.

If it is possible, I can imagine a civilization that could be billions of years old, but a long, long ways from us. But if you can find a stable, livable orbit there, it seems a great place to be safe for a long, long time! Maybe they are retirement communities for civilizations that have the since to survive a billion years or more.

The planetary capture is possible, but not likely. If 2 stars and a planet had a close encounter, its possible that the planet could be captured into a stable orbit. But if such close encounters were possible, they would be more likely to strip planets away from stars. I'm not sure of the density in GCs, (I guess I could Google it), but I'd guess that even there that close stellar encounters are not extremely common. But it only takes 1 close stellar encounter in a star's multi-billion year existance to strip away all planets it might happen to have.

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Astrophysical metals.

I think the odds are slim because globular cluster stars are dominated by low mass stars, and they don't supernova. At most you eventually get planetary nebulae. Transit searches for large planets ("hot Jupiters") in globular clusters have found no planets at all so far, suggesting that the low metalicity environment is not conducive to planet formation (i.e., Gilliland, et al., 2000; Weldrake, et al., 2005; Weldrake, Sackett & Bridges, 2007; Weldrake, Sackett & Bridges, 2008).

The odds are extremely small, if not zero, that a planet of any mass could be captured. As already noted by tony873004, planets get flung off into space, not captured, in stellar encounters. The planets have to form around their host stars, and then avoid getting ejected in a close encounter. Hence, the place to look is in the outer regions of a globular clusters, where the density of stars is relatively low. There are a lot more close encounters near the core of a globular cluster. But, as noted above, searches so far have come up empty, even when that was not expected.

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Thank you for the links to those papers! Very illuminating (so to speak).

Just because they're "low metal" don't mean they couldn't have planets, just less of them, see http://en.wikipedia.org/wiki/Methuselah_%28planet%29

Why is everyone here taking "low" as "no"?

We dont have a Hot Jupiter here either and these are mostly arouund stars with higher metallicity than our Sun.

They are not common, just we can see Hot Jupiters very easily.

Good point - you can have lots of gas giants without metals - look at the low density of Saturn - the whole planet is less than a gram/cc.

I am still working to digest those papers and they to put some more thoughts into type. I have not groked the fullness yet.

Okay, so we've looked at some cluster and there was no evidence of big Jupiter-sized planets during the time we looked. But we looked at a whole bunch of stars at the same time and that means even if gas giant took years to transit, we might have caught one. Still, I do not think we have ruled it out. There are all lot more clusters of a lot more stars out there.

And we have an example of a planet around a pulsar in a globluar cluster!

And just because clusters do not have much metal does not mean they have zero metal. In the early days, there were giant that burned out quicked and some when supernova, right? And given the closeness of these stars, the chances for interactions that led to supernova events is not zero.

And though the tendacy for a planet formed outside the well of a star is to be throw out, that same density of stars might allow one or two be slowed and captured?

I think we are a long way to saying there is no change of a terrestrial planet in a globluar cluster. But also a long way from commiting any large amount of resources to find one, given the likelihood of failure.

I believe my dream of five billlion year old civilization is safe but still science fiction. <sigh>

There are binary systems in globular clusters so if you can get multiple objects forming in one system, why not a gas giant and a star? The lack of metals is a big problem though since you seem to need heavier elements to form planets. Globular clusters have a fraction of the sun's heavy elements but there's still pulsars/neutron stars found in them so perhaps somewhere there might be a planet.

Of course what's the chances of a star (around which planets can form) forming from the gas of a supernova remnant in the crowded enviroment of a globular cluster?

You have SOME heavy elements, you can have even rocky planets, just not as abundantly, ruled out?!Eh, we cannot say ANYTHING after 13 years of research, sorry.

I've been reading and listened to "Astronomy Cast Ep. 75: Stellar Populations" tonight. And it is really not looking good for planets in the interior of GC's. I had known about Pop II and Pop I stars but the first generation Pop III supergiants are new to me. They are all gone and we have metals left from them. They would have left supernova remnants and though the eons, we would have contributions from planetary nebula-type events (but limited to lighter than iron) and an occasion nova.

But the closeness of the Pop II stars will clear the debris, both by wind and gravity interaction. Still with the time it takes for a cloud to leave the cluster, it seems it could condense into a planet or two. But it seems it would find a stable place to orbit, maybe not until it got to the parameter of the cluster, unless it was accelerated beyond escape velocity.

It seems the structure-of-the-cluster (that would make a good rap song!) is such that over time, there is a selection of big objects toward the center and smaller toward the outside. Maybe there are gas giants that orbit the cluster independently with chromosyntheic life on Europa-like moons. Can an earth-type planet support photosynthesis orbiting a white dwarf? The inhabitable zone of that system is going to be small and the spectum will be very different.

So, I am not as jazzed about this as I was, but I believe it is possible. Barely. And so hard to detect at this distance, this funding to look for them is not going to be an issue. Not when we are talking about turning off working Mars Rovers! Thanks, this has been fun and educational.

Still, there are sooooo many clusters with sooo many stars. "It would be such a waste of space".

Well, there are some young globular clusters, I've read about some a few years go.

I would say that the odds of stable planetary orbits around a star in a GC are very low. The orbits of stars in a GC are not circular. They are highly elliptical and even a star on the periphery of the GC has been near the crowded center before and will be again!

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