In this clip from Genius by Stephen Hawking, discover the essential factors that make a planet suitable for life. Having liquid water and an atmosphere are considered to be the two most important factors when searching for possibilities of alien life. The distance of a rocky planet's orbit from its star is critical to whether there can be liquid water. Too hot and the water will boil and turn to steam, too cold and it will freeze. Scientists refer to the zone of perfect conditions as the Goldilocks Zone. The volunteers set out to challenge this theory using an ice cube and a metal bar to demonstrate how liquid water could be present far from any star.