On the chart you instantly notice that Earth is the smallest of all those planets.
I’ll guess that gravity might limit the optimal size of living things on many of those planets.
I wonder if self-propelled flight is possible on some of those really large planets?
Yes, the title is misleading. These planets may be in the “habitable zone”, but no exoplanet has yet been discovered that would actually be habitable as far as humans are concerned.
Its also possible that some of those planets may be closer to earth mass but have large moons that we can’t currently spot.
The gravity of these planets will have been what it is — IOW, whatever chances to live there has always lived in those conditions.
A sidebar (the Moon is about 1/100th the mass of Earth)
Your Weight on the Moon
http://www.vat19.com/brain-candy/your-weight-on-the-moon.cfm
another (Mars is about 1/8th the mass of Earth)
http://wiki.answers.com/Q/How_much_would_a_200-pound_person_weigh_on_the_planet_Mars
If the larger planets shown have an earth similar gravity, it would be due to a lower density and would probably preclude having a fractionated and molten or partially molten core to generate a significant magnetic field (a dynamo-core).
That magnetic field comes in handy for keeping the solar wind from hinking up the atmosphere and making life tougher on the surface.
While I don’t think it’s a barrier to life, it would be a lot more difficult to get established there and would probably lead to indigenous species that were quite a bit tougher than earth based life.
Higher gravity would probably mean they have the dynamo-core, so radiation would be limited to good levels at the surface, and then there could be some interesting critters in that environment too. Either super lithe/lightweight or super dense in muscle with maybe a harder material evolved for bone formation.