Exoplanets should have exomoons

WRITERS of science fiction have long assumed that the galaxy is teeming with alien planets. They were correct, but it was only in the past few decades that science has been able to confirm this. The first exoplanet was discovered in 1992, but the floodgates really opened in 2009, with the launch of , a planet-hunting space probe. Thousands have since been found. Statistics suggest that every star in the galaxy—and, presumably, the universe—has at least one.’s fuel is now almost exhausted, and the probe is nearing the end of its life. But a paper published by Alex Teachey and David Kipping in suggests that data it has already collected may confirm another science-fiction assumption—that alien planets have alien moons. In a way, this is not surprising. Few astronomers would have bet against the existence of exomoons. But they might have been sceptical that was sensitive enough to spot any. What’s more, the moon that Drs Teachey and Kipping propose is strikingly strange.