Is Pluto made out of ice--as in frozen water? If so, wouldn't that provide evidence for alien life in the cosmos?
closed as off-topic by Peter Shor , Waffle's Crazy Peanut, Qmechanic♦ Jul 24 '13 at 18:53
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There seems to be an impression floating around that water is somehow rare and special in the universe. This is just plain false. Water is a rather natural thing to expect whenever there are both hydrogen and oxygen around. Now hydrogen is the most common element in the universe, and oxygen is the third most common, depending on how you count. Wikipedia has a nice summary of abundances.
In fact, anywhere where the ambient temperatures and pressures allow water molecules to form, you generally expect to find them. In fact, in theories of planet formation from a disk of material around a young star, there is the concept of the ice line outside of which planets grow more easily due to the solidification of volatiles like water and ammonia. In other words, the outer planets are expected to have lots of water-ice, and in fact that's what helped them form in the first place.
What is more interesting is the presence of liquid water. Why? Well, our (admittedly biased) experience on Earth tells us life simply needs a good liquid solvent. Biochemistry all happens in water to some extent or another as far as we know. Now this doesn't mean life cannot exist without liquid water, or that any liquid water will necessarily have life, but in looking for life in the cosmos, starting with places that have liquid water seems like a good bet.
Now Pluto is suspected to have large amounts of water-ice (and other ices). Its exact composition, however, is an open question. Previously, all we could do was
by looking at it from here on Earth. That leads to some information but not too much. In just under two years, the New Horizons spacecraft will be the first to ever get close to Pluto to make more detailed measurements. One of the ideas that has been floating around for the past several years is that maybe there is enough natural radioactive decay happening inside Pluto to keep part of the interior liquid. We will have to wait to see if it really does have a subsurface ocean.1
So in summary: Pluto almost certainly has water ice, as do most of the small bodies in the outer Solar System. Water ice and vapor are in fact quite common. There is a question of whether liquid water exists on Pluto or anywhere in the Solar System besides Earth, and we do not know the answer, yet. Finally, having liquid water may very well be neither necessary nor sufficient for life to form, and certainly having water-ice is nothing special regarding life.