Modeling of super earths suggests that a rocky planet lying in the habitable zone is not enough to create a habitat. The theory of planetary formation says that planets form from proto-planetary disks which are essentially accretion disks around young stars. In these proto-planetary disks clumps start to form and increase in size through gravitation with other clumps eventually forming planets. The planetary disks should be abundant in hydrogen and this hydrogen will be gravitationally attracted to the forming planets. The size of the planet will dictate the gravitational force and thus how much hydrogen gas collects around the planet. The young star the planets are forming around will also be stripping away hydrogen through radiation pressure. By modeling the balance of capture and removal rate of hydrogen Dr. Helmut Lammer of the Space Research Institute (IWF) of the Austrian Academy of Sciences was able to show that under similar conditions as our own solar system a rocky planet with 0.5 the radius of the earth would not capture enough hydrogen and would not likely support life. Alternatively a rocky planet with a radius 1.5 times that of the earth would capture to much hydrogen and form a thick atmosphere that would not likely support life. Dr. Lammer's research suggests that for some of the recently discovered rocky planets, such as Kepler-62e, being in the habitable zone does not make them habitable planets.
http://www.sciencedaily.com/releases/2014/02/140226074925.htm
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