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<div class="moz-cite-prefix">On 2013-11-22 11:56, Eugen Leitl wrote:<br>
</div>
<blockquote cite="mid:20131122115612.GR5661@leitl.org" type="cite">
But for emergence of life, you will need molecules in a
solvent, and only water has a 4 C density anomaly. There
might be transient uses of cryogenic hydrocarbons, or
water/ammonia
and hydrogen disulfide, and condensation from gas phase into
solid state with subsequet irradation, but for life you'll
need a solvent, and it's almost certainly always water.<br>
</blockquote>
<br>
I think we might be too hasty in ruling out other thalassogens. <br>
<a href="https://en.wikipedia.org/wiki/Thalassogen">https://en.wikipedia.org/wiki/Thalassogen</a><br>
For rpg purposes I have been looking at exotic biochemistries, and I
was surprised by the number of liquids that may exist in solar
systems.<br>
<a
href="http://www.ifa.hawaii.edu/%7Emeech/a281/handouts/Baines_astrobio04.pdf">http://www.ifa.hawaii.edu/~meech/a281/handouts/Baines_astrobio04.pdf</a><br>
<br>
Water is perhaps the most abundant one, but one should not rule out
ammonia - outside the ice line, especially if you get planets
spiralling in from the colder parts, ammonia is very common. It can
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
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.<br>
<br>
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.<br>
<br>
<a
href="http://blog.practicalethics.ox.ac.uk/2013/11/invasion-from-the-blue-planet-are-we-protecting-mars-too-much/">http://blog.practicalethics.ox.ac.uk/2013/11/invasion-from-the-blue-planet-are-we-protecting-mars-too-much/</a><br>
<br>
<pre class="moz-signature" cols="72">--
Dr Anders Sandberg
Future of Humanity Institute
Oxford Martin School
Oxford University
</pre>
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