The field of astrobiology has its critics, mainly those who assume that life outside of earth does not exist. However, recent developments in the field have demonstrated that a planet does not have to be a simulacrum of earth to house life. For example, the "resonant interplay of moons in multi-satellite systems leads to an endless tug-and-squeeze that can generate more than enough heat to keep large reservoirs of water in a liquid state, and provide localized sources of energy (such as the churning vents found on ocean floors) that could fuel biology."

http://www.space.com/searchforlife/080306-astrobiology-picture.html