A red dwarf star 20 light-years away is again providing hints that it hosts the first definitively habitable planet outside our Solar System.As Thomas Gold points out at the end of his paper, "The Deep Hot Biosphere," there most likely is life on other planets, but this life is most likely in the ground and not the surface. So, what ever life there is in the rest of the solar system or galaxy or universe, it's probably at the bacterial stage. To achieve complex, surficial, and large life, you need the gateway of the Oxygen Evolving Complex, in the photosynthesis process. To obtain large life as we know it, life that can power the kinds of brains we have, brains that can formulate theories and make machines that are powerful enough to look at distant stars and find other worlds, you need an atmosphere with lots of oxygen. This byproduct of photosynthesis protects and provides a powerful form of respiration. A world will need something like the miraculous unification (PSII and PSI) of the Z-scheme (pronounced "zed") to get animals like us going about its surface.
The planet Gliese 581d is at the colder outer edge of the "Goldilocks zone" in which liquid water can be sustained.
But there is something else...
Getting to any habitable planet will certainly require something that looks like the spaceship, Icarus II, in the movie Sunshine:
If people ever journey for extended periods in outer space, endeavor will never be as machinate and barren as Star Trek. The vision of sterile engineering emancipating us from our planetmates is not only tasteless and boring, it borders on the hideous. No matter how much our own species preoccupies us, life is a far wider system. Life is an incredibly complex interdendence of matter and energy among millions of species beyond (and within ) our own skin… Without “the other” we do not survive.Indeed, Sunshine, a generally bad film, gets this one thing correct: space travel will mean traveling with other living organisms.