[ExI] Double-Earth (Was: kepler study says 8.8e9 earthlike planets)

[Anders Sandberg]

On 2013-11-22 18:19, Kelly Anderson wrote:
> On Fri, Nov 22, 2013 at 6:38 AM, Eugen Leitl <eugen at leitl.org 
> <mailto:eugen at leitl.org>> wrote:
>
>
>     > Water is perhaps the most abundant one, but one should not rule out
>
>     Water is not particularly abundant, but it has certainly very
>     interesting properties, which, if taken together, make it unique.
>
>
> I tend to agree with Eugen on this one. As far as I'm aware, water is 
> the only liquid that becomes less dense upon freezing. Otherwise, the 
> oceans would fill up with ice from the bottom up. Ices are clearly not 
> as good for life as liquid.

Remember the high temperature water ices of double-earth: under many 
conditions water behaves "normally" too. In fact, bottom-ice-free oceans 
might be unusual in the universe if most terrestrials tend to be big 
waterworlds.

There are other expanding liquids like beryllium difluoride, but most 
are elements like silicon, bismuth, antimony, gallium and plutonium. 
Even I agree that a planet with plutonium oceans is unlikely to be 
habitable for life.

While we all know the anomalous properties of water and cherish them, it 
might be because we also live in a water-dominated environment where 
every little property has big effects on us. Had we been living in a 
methane or high pressure water-ammonia environment we might have written 
the same number of papers about the anomalousness of methane and 
water-ammonia mixtures.


-- 
Dr Anders Sandberg
Future of Humanity Institute
Oxford Martin School
Oxford University

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