Wobble
Hollywood has fed us with visions of what aliens look like, but rarely paints a picture of where they might live. Dr David Kipping and colleagues from the Department of Physics and Astronomy at University College London, have devised a method for detecting moons in other solar systems that could support life.  Dr Kipping had originally been working on the phenomenon of ‘transiting planets’, when a planet passes in front of a distant star. The planet appears to get a little bit dimmer and he was modelling such affects, making equations that could accurately map the motion of the planet as it moved across the star. ‘When the planet passes in front of the star,’ says Kipping, ‘it gives us information about the position and velocity of the planet. As the planet is orbiting around the star, it is also orbiting its moon. There’s this little deviation, this little “wobble” as it goes round. We can essentially look for these wobbles, look for the changes in position, and changes in velocity, and see if it’s the signature of what a moon would create.’

Rocky planet
But to be habitable, these moons would need conditions to be just right. ‘Conventionally, what people define as habitable is that it’s a rocky planet,’ says Kipping, ‘so it can have liquid water on the surface. Everything on our own planet requires water to have life, so you need a temperature in between zero and 100 degrees. The planet can’t be too close or too far away from the star.  It needs to be the right distance from the star so it’s not boiling, and not freezing.’ A magnetic field would also be useful, because just like earth, it would protect it from radiation.

Exomoons
These ‘exomoons’ could currently be spotted by an instrument with the power of  NASA’s Kepler Space telescope, but within five years Kipping believes, ground-based telescopes will be ‘surpassing what Kepler can do’. The search for habitable moons could rapidly open-up. Kipping has had good feedback, including some from unlikely sources. ‘We have a very positive response form a lot of people,’ he says, ‘I’ve had emails from teenagers in India quite recently saying “I really enjoyed reading your paper, I’m only a 14 year old amateur, but I’d like to use your techniques.”’