Tardigrades were the starting point of this story. They really do exist, and really are able to come alive again after complete dehydration, but they are actually terrestrial animals. We don’t notice them because they’re absolutely tiny, but they are very common, living in places which are alternately dry and wet, such as puddles and gutters. They’re fat little things whose chubby legs have little claws on the ends of them, and they’re sometimes called ‘water bears’. Here’s a youtube clip.
If tardigrades were intelligent, they would make perfect space travellers. No need for food or air. No need to worry about the length of the journey.
I first encountered them when I was a student in the 1970s and did a subsidiary course in zoology. The lecturer demonstrated that, if you cut a dried-out tardigrade in half and then rehydrated the pieces, they would first come alive, and then die.
Scientists, eh? What are they like?