The search for life outside of Earth has taken many forms. Mars, our neighbouring world, looks like it was once habitable. Perhaps too Venus, despite its current hellish conditions. But in recent years, scientists’ gazes have been drawn elsewhere. What about the moons of Jupiter? Three of Jupiter’s four largest moons are icy, and in 1998 NASA’s Galileo spacecraft detected tantalising hints of an ocean beneath one, Europa. Since then, further studies have detected signs of water plumes possibly erupting from this ocean. The other two large icy moons, Ganymede and Callisto, are also thought to have oceans beneath their surfaces. Now, new questions are being asked: if there is water on these moons, could there be life? And could we look for it?