Where Is the Habitable Zone for M-Dwarf Stars?

If orbiting planets huddle close enough to an M-dwarf, in theory they could fall within the habitable zone where surface liquid water, and thus life, is possible. Yet, an M-dwarf's habitable zone is poorly understood. Because planets in this range orbit so close to an M-dwarf they may be tidally locked, said Ravi Kumar Kopparapu, an assistant research scientist at the NASA Goddard Space Flight Center in Maryland.