Seth Shostak, a senior astronomer at the Search for Extraterrestrial Intelligence Institute (SETI) talks to Good Magazine:
GOOD: Why is water so important for life?
Seth Shostak: Imagine taking your old chemistry set out and dumping it onto the living-room floor. Not much happens, except maybe your mom gets upset. Now, if you bring over a pail of water and throw it on top, then something will happen. Water is great for life for that very straightforward reason: It’s good for chemistry.
G: Couldn’t you just use another liquid?
SS: Yeah, in principle. But if you actually look at the kind of things that would be liquid, and that might be on planets you can imagine, water still comes out as the best fit. One of the reasons for that is that water is liquid over a very wide range of temperatures: 33 degrees to 212 degrees Fahrenheit. These other liquids you might find—ammonia, methane, those sorts of things, maybe even liquid hydrogen on the surface of Jupiter if you had that—they’re only liquid in a very small and unfortunate range of temperatures.
G: So how much water is there in the universe?
SS: Hydrogen is the number one element in the universe. Three-quarters of the universe by weight is hydrogen. And the third most popular element in the entire cosmos is oxygen. There’s a lot of H and a lot of O, and when they get together you get water. So there’s a lot of water out there.
