The habitable zone around a star is defined by the range of orbital distance within which liquid water can exist on a planet.
However, both Mars and Venus in our solar system exist roughly within the Suns habitable zone but neither has liquid water. We are told both had liquid water in the past.
It would seem to me that both edges of the habitable zone experience runaway effects that get rid of any liquid water on the planet. Are the processes likely to occur on any planet? If so, the idea of a habitable zone might have to be rethought slightly.
Another thing I'm wondering, is that Earths rotation rate is unusual for a planet in this position because of the presence of the moon. Would a normal planet sitting where we are suffer either of the fates of Mars or Venus?