I'm not a biologist, but here's a fascinating article on the subject: http://m.nautil.us/blog/forget-earth_likewell-first-find-aliens-on-eyeball-planets http://

I'm not a biologist, but here's a fascinating article on the subject: http://m.nautil.us/blog/forget-earth_likewell-first-find-aliens-on-eyeball-planets http://m.nautil.us/blog/forget-earth_likewell-first-find-ali... TL;DR is that there may exist a band around the planet where the two zones meet that is habitable. I think it's a reasonable supposition that most of the rest of the planet would be uninhabitable.