The article states:
Now, though, it's becoming increasingly clear that the question of what makes a planet habitable is not as simple as finding it in just the right spot. Many other factors, including a planet's mass, atmosphere, composition and the way it orbits its nearest star, can all influence whether it can sustain liquid water, an essential ingredient for life as we know it. As astronomers explore newly discovered planets and create computer simulations of virtual worlds, they are discovering that water, and life, might exist on all manner of weird worlds where conditions are very different from those on Earth. And that means there could be vastly more habitable planets out there than we thought possible. "It's like science fiction, only better," says Raymond Pierrehumbert, a climate scientist at the University of Chicago, who studies planets inside and outside of our solar system.
Near the end of the article is this:
Last year, a team of astronomers led by Stéphane Udry of the Geneva Observatory, Switzerland, discovered Gliese 581c, the first likely rocky planet orbiting a sun-like star in another solar system.Given the size of its orbit around its star, initial calculations suggested it should be in the Goldilocks zone - at about the right temperature for liquid water. But other scientists soon pointed out that if it had an atmosphere containing greenhouse gases, it would most likely be far too hot for liquid water. However, the same effect could make a planet called Gliese 581d, orbiting further out round the same star, suitable for life.Then again, Gliese 581d may be too big to be a rocky planet. The team that discovered the planets point out that Gliese 581c could still be habitable if it is very cloudy, and it remains the best candidate so far for a habitable planet in another solar system. With new planets being discovered all the time, though, there are sure to be others.
Naturally, all of this science conjecturing complicates the philosophical, ethical and religious fields of study. The complication is this: are the theorums and theories of these fields of study earth-bound or do they apply to all creatures, alien and all?