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Is Pluto made out of ice--as in frozen water? If so, wouldn't that provide evidence for alien life in the cosmos?

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closed as off-topic by Peter Shor , Waffle's Crazy Peanut, Qmechanic Jul 24 '13 at 18:53

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Ice (or water) is not sufficient for life ... –  fffred Jul 18 '13 at 21:14
    
This article says that it is: universetoday.com/13875/what-is-pluto-made-up-of –  Ramin Jul 18 '13 at 21:14
    
@fffred, how come all the documentaries about mars seeks to find water on mars for proof of alien life? –  Ramin Jul 18 '13 at 21:15
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We tend to find life where there is water on earth. This suggests some sort of correlation. A "soft" correlation would be that water is needed for life (as we know it). A "strong" correlation would be that where-ever there is water, there is life. At the moment, it's more accurate to assume the soft correlation. Water is certainly not the only prerequisite for life and is therefore in itself not proof of alien life. –  Wouter Jul 18 '13 at 21:20
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Pluto made of frozen water = evidence of alien life in the cosmos. Hmmmm... to say that there is a logical gap in there might be criminally understating the nature of this "argument". –  Alfred Centauri Jul 18 '13 at 21:48

1 Answer 1

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

  • estimate how reflective its surface is or
  • estimate its density

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.


1 Of course, if all you want is liquid water underneath a surface of ice, there are slightly closer candidates in the Solar System, including Jupiter's moon Europa or Saturn's moon Enceladus.

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That's a very detailed and informative response to whether or not pluto has water, but it doesn't say anything about alien life. The comments, however, suggest that water is in no way an indicator of alien life, but just a soft correlation. –  Ramin Jul 19 '13 at 0:33

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