“Water is ridiculously common, one of the most common molecules in the universe,” said Nicolas Cowan, an astronomer and astrobiologist at the University of Washington in Seattle.
What seems rare is finding water in liquid form. In space, it either vaporizes if it is too hot or freezes if it is too cold .
“The only time you ever find it stable as a liquid is when you get enough atmosphere down to provide enough pressure to keep it liquid,” Cowan explained.
Scientists looking for aliens consider liquid water “the Holy Grail, the thing that people really want to find,” Cowan said. “Water is the main requirement we can see that life on Earth seems to have.” Although life also needs a source of energy of some kind, in many ways, “you don’t have to worry too much about that,” Meyer added, since Earth shows that life can live off many different kinds of energy, from the sun or heat or chemicals.
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