Our solar system is a lot like the story of Goldilocks and the Three Bears. Planets that are located close to the sun can be too hot, while those located further from the sun can be too cold, making ...

Relative sizes of the newly discovered habitable-zone planets and Earth. Left to right: Kepler-69c, Kepler-62e, Kepler-62f and Earth (except for Earth, these are artists' renditions). Image credit: ...