The climate on such a world must be beyond bizarre. (Image credit: MARK GARLICK/SCIENCE PHOTO) A super-Earth planet that dips in and out of its star's habitable zone has been discovered just 19.7 light-years away. The planet, known as HD 20794d, gets farther out from its star than Mars is from the sun and, on the other end of its orbit, as close as Venus. Each orbit the plan