Does a planet have to be just like Earth to support life? NASA isn’t sure. Here we see an artist’s conception of a planet around a star that is cooler than our sun — these are called M-dwarfs and brown dwarfs. It is still unclear if cooler stars can support young planets with the same life-forming chemical mix that began life on Earth. For a planet to sustain life, it must be able to carry water below boiling point yet above freezing. In addition, it must have enough air — but not too much. This delicate balance depends on the proximity of the star to the planet.