Whether or not we are alone in the universe is one of the most profound questions that humanity can ask. In this short video David Kipping, an astronomer at Columbia University in the US, takes a fresh look at the conditions required to support life. Specifically, Kipping takes issue with the definition of the so-called "habitable zone" – the band surrounding a star within which water could exist in liquid form on the surface of a planet. Kipping points out that the requirements for life are complex and this definition is based on the fact that all known life forms here on Earth require water. What if that is not universally true?

This video is part of our 100 Second Science series, in which researchers give concise presentations covering the spectrum of physics.