YEARS ago, when David Kipping lived in London, he would walk home through the city and look up at the moon. As an astronomer, its faintly glowing presence served as a nightly source of inspiration. “It was a reminder that moons were waiting for us around exoplanets,” he says. “It just made sense that we should look for them.”
Finding exomoons – natural satellites of worlds beyond our solar system – would be thrilling. For a start, they may play a key role in determining the habitability of host planets by damping their wobbles, fostering a stable climate in the same way that our moon has done for Earth. They might also come in weird and wonderful configurations, such as rings of moons and moons with their own moons. But most excitingly, it is possible that some of them are more hospitable to life than exoplanets.
Kipping, now at Cornell University in New York, is part of a small community of astronomers who search for exomoons. The statistics, at least, are on their side: we have found some 5500 exoplanets so far, and some of these could have dozens of moons. The trouble is, proving their existence isn’t straightforward. The two sightings Kipping has made so far are hotly disputed.
But now, hope is on the horizon, with a host of new ways to search for these objects – from watching rogue planets that have abandoned their stars to monitoring the gravitational wobbles of exoplanets. Armed with these new techniques, and with new telescopes on the way, the moon…