From: Anders Sandberg (asa@nada.kth.se)
Date: Wed Aug 06 2003 - 01:42:09 MDT
On Tue, Aug 05, 2003 at 06:32:32PM -0500, Kevin Freels wrote:
>
> Now I am not a physicist, but doesn't the fluidity of water depend on
> more than jus tthe distance from it's star and the heat from it?
Water is a fluid for a certain range of pressures and temperatures; it
is the green region in the phase diagram
http://www.martin.chaplin.btinternet.co.uk/phase.html
So you could get liquid water in a larger temperature range by having a
greater pressure; above 21.671 MPa you pass the critical point and
liquid and vapor pass seamlessly into each other (see Hal Clement's
novel _Close to Critical_).
You can also extend the range of the planets by having the temperature
kept in a milder range as you say. The problem is that warm planets will
have water vapor in their atmospheres and it is a greenhouse gas, so you
get a positive feedback. Cold planets will tend to get much ice, and it
is a good reflector and will make the planet colder, producing a
snowball (where liquid water can still persist under the surface, as it
likely did on Earth in the precambrian and right now on Europa).
> It seems to me that the people conducting these searches are limiting
> themselves by putting a "habital" zone around a star.
Most searches are system-wise, so the exact extent of the lifezone is
not important. But plenty of arguments about the probability of life
depends on its average size, and a larger lifezone makes life more
likely.
However, people are indeed expanding the range of places where life
would not be unexpected. Some have suggested moons of gas giants a la
Europa, and brown dwarves might have lifezones of their own.
-- ----------------------------------------------------------------------- Anders Sandberg Towards Ascension! asa@nada.kth.se http://www.nada.kth.se/~asa/ GCS/M/S/O d++ -p+ c++++ !l u+ e++ m++ s+/+ n--- h+/* f+ g+ w++ t+ r+ !y
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