Hydrogen blows up the habitable zone.

The article focuses on planetary research. It states that researchers Raymond Pierrehumbert of the University of Chicago and Eric Gaidos of the University of Hawaii calculated that a thick atmosphere of hydrogen on Earth-sized planets and super-Earths could provide greenhouse warming at distances outside the habitable zone of most stars but would still allow enough sunlight to reach the planetary surface and foster photosynthesis. It talks about the difficulty of detecting such distant planets.