Lots of great discussion today! This week there was a special exoplanet edition of Science magazine and Dr. Sara Seager had an article published in it.
Dr. Seager presents a new, expanded definition of planetary habitable zones.
Here is a link to her paper:
http://www.sciencemag.org/content/340/6132/577.abstract?sid=f1b791f3-9a70-4d2d-912e-09f40efa1deb