An alien planet declared a super-Earth by NASA might not be so habitable after all. New measurements flag the planet (called Kepler-69c) as more of a "super-Venus" that would likely be inhospitable to life.
The planetary status change is part of a larger struggle over how to define the habitable zone of a star. In recent years, scientists determined that the distance between a planet and its type of star is just one metric that hints at the likelihood of liquid water on its surface, which could fuel life. Other factors include the planet's atmosphere and even how the star behaves.
"There are a lot of unanswered questions about habitability," astrophysicist Lucianne Walkowicz, Kepler science team member at Princeton University, said in a statement. [The Strangest Alien Planets (Gallery)]
"If the planet gets zapped with radiation all the time by flares from its parent star, the surface might not be a very pleasant place to live. But on the other hand, if there's liquid water around, that makes a really good shield from high-energy radiation, so maybe life could thrive in the oceans."