Paul Fuller <pgf### [at] optusnetcomau> wrote:
> Makes you wonder what life on a Kuiper Belt Object might be like.

  I don't think it would be physically possible for any kind of life to
form that far from the Sun.

  Chemicals need to react with each other, which means that there must be
some kind of solution where they can freely float or otherwise move.
This usually means some kind of liquid. Obviously some kind of energy is
also needed or else nothing will move.

  Water would be the liquid of choice because it has two very special
properties that basically no other liquid has: It's extremely common,
and its solid form has lessed density than its liquid form. Without these
two properties there would be no life on Earth (or anywhere else). (There
are probably also many other necessary properties, related to solubility
and how water reacts chemically with other compounds, but I do not know
enough about chemistry to say anything about that.)

  It's hard to imagine how life could form without water.

  Of course for the water to be any good, it has to be in liquid form.
If you are too far away from the Sun, all the water will be frozen solid.
This isn't a very fertile ground for life to form. There are little chemical
reactions going on, chemicals are not very free to move, and there are
probably a huge bunch of other properties necessary for *any* kind of
life to form which just aren't possible with deep-frozen ice.

  Now, perhaps if there was a liquid which remains an liquid form at those
temperatures, it could ostensibly happen. However, such liquids are both
extremely rare (iow. there wouldn't be enough of it in any given planet),
and their chemical properties are probably inadequate for any kind of
lifeforms. (Also, most liquids other than water get denser when they
solidify, which is a big problem.)

  (Conversely, a planet which is too *close* to the Sun cannot form life
either, this time because there's no water because it's all vaporized away.
It also makes forming a viable atmosphere quite hard, making it a very
hostile environment, where strong radiation hits directly the surface
of the planet, destroying any complex chemicals that might form by chance.)

-- 
                                                          - Warp

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