Scientists are working to rule out non-biological explanations for conditions present on Titan, a moon of Saturn, that suggest there could be life on the moon's surface. "'Scientific conservatism suggests that a biological explanation should be the last choice after all non-biological explanations are addressed,' says Mark Allen of NASA's Jet Propulsion Laboratory. 'We have a lot of work to do to rule out possible non-biological explanations.' Jonathan Lunine of the University of Arizona, a member of Clark's team, agrees. But he says it may not be possible to distinguish between biological and non-biological explanations without additional missions to Titan. "The only way to know for sure would be to actually get hold of an organism and show that it is alive," he told New Scientist.