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<Link> Discovered! Most Earth-Like Alien Planet & 2 Other Possibly Habitable Worlds
#1
http://www.space.com/20720-earth-like-al...overy.html

While I think this report might be a tad on the hopeful side, it does bring to the forefront serious consideration for systems such as this....
A room without books is like a body without a soul --Cicero
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#2
So what are the chances such a world would have an Earth-like mix of continental crust and oceans? Are there any papers on the expected surface water fraction of Earth-like worlds?

We have subtypes such as Lacustric Gaian, Paludial Gaian, Eugaian, Bathypelagic Gaian and Panthalassic, but which is the most likely scenario for a terrestrial with about I Earth-mass?
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#3
I would note, by the way, that 'habitable' in this context seems to mean 'a potentially life-bearing world'. There is no guarantee that these worlds do have life, and it seems quite unlikely that many of these worlds would be able to support unmodified human life.
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#4
Even if they are water worlds - and I presume there is some basis for that assertion, such as Sol-like elemental abundances in the parent star so that the planets wouldn't be carbon-rich worlds with an ocean of crude oil instead of water - that still doesn't mean they would be suitable for Earthly life. One possibility, for example, is that they would have life but with a radically different genetic code and/or different proteins. AFAIK, Earth life's DNA and RNA bases are far from being the only purines and pyrimidines possible - and there are a heck of a lot more amino acids than the limited set Earth life uses. And, of course, there is the issue of chirality.

On top of that, we have no proof at all that a water-based form of life with COMPLETELY different chemistry isn't possible.
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#5
(04-20-2013, 04:45 AM)stevebowers Wrote: I would note, by the way, that 'habitable' in this context seems to mean 'a potentially life-bearing world'. There is no guarantee that these worlds do have life, and it seems quite unlikely that many of these worlds would be able to support unmodified human life.

This is something a lot of science fiction ignores. The odds that a very earth-like planet, even one that is earth-like enough to support complex life, would be a 'shirtsleeves' environment for baseline humans is probably very, very small. To take just one factor, our own planet is near the inner edge of the habitable zone, and so has a very, very low percentage of carbon dioxide in the atmosphere. A planet otherwise just like earth but elsewhere in the habitable zone would have much more, perhaps up to a bar or more of atmospheric pressure, just to maintain liquid water at the surface (something that would happen more or less automatically, given the way the carbon cycle works, on an earth-like planet). That would be fatal to most air-breathing vertebrates, including humans, because of the way our physiology works.
Stephen
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