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

[Eugen Leitl]

On Fri, Nov 22, 2013 at 01:23:58PM +0000, Anders Sandberg wrote:

> I think we might be too hasty in ruling out other thalassogens.
> https://en.wikipedia.org/wiki/Thalassogen

I would rule most of them as a stable end point. This is not
ad hoc, I've spent some time investigating different options.

> For rpg purposes I have been looking at exotic biochemistries, and I
> was surprised by the number of liquids that may exist in solar

You don't need just liquids. You need liquids with a wide liquid
range and redox stability. If you have significant oceans you better
have a density anomaly, too.

Chemistry dominates over physics here.

> systems.
> http://www.ifa.hawaii.edu/~meech/a281/handouts/Baines_astrobio04.pdf <http://www.ifa.hawaii.edu/%7Emeech/a281/handouts/Baines_astrobio04.pdf>
> 
> 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.

> ammonia - outside the ice line, especially if you get planets
> spiralling in from the colder parts, ammonia is very common. It can

Ammonia stops being common rather soon, as nitrogen-nitrogen
bonds are so very stable.

> coexist with water in a lot of phases, and has a pretty interesting
> chemistry (dissolving and complexing with metals allows for some
> funky things). Methane and nitrogen are other options. While often

Cryogenic (so everything is dead slow but radical reactions, which
leave you with kerogen-like brick) and apolar. Useful for prebiotic stages, 
but, then, pretty much everything is useful for that.

> dismissed as having too limited temperature range to be likely
> liquids, their range goes up a lot under pressure. Sulphuric acid,
> liquid hydrogen, and supercritical gases might be rare, but the more
> exotic solvents there are, the number of spots in the universe where
> life could exist goes up by a fairly sizeable factor.

I disgree. Complex life will need water. Water/ammonia for ice worlds, 
maybe.
 
> Maybe ocean worlds, ice-capped seas or hothouses are dead ends from
> an intelligence or technology standpoint. But that still leaves
> plenty of weird options. We do not care much about what the majority
> of atoms do: it is the few spots that produce self-propagating
> formed integrities that really matter.
> 
> http://blog.practicalethics.ox.ac.uk/2013/11/invasion-from-the-blue-planet-are-we-protecting-mars-too-much/