The hunt for the first exomoons

If our Solar System is any guide, moons should exist in abundance throughout the galaxy — perhaps reaching numbers as high as tens of billions.

David Kipping was almost shaking with excitement. He was staring at a plot on his computer screen with a peculiar dip that kept reappearing no matter how he processed the data. It looked like the first glimpse of a moon beyond the Solar System.

He left his desk and went for a walk. “I had to sit on a bench and take deep breaths to try and centre myself a bit because I was just, like, crazily excited about it — thinking ‘This is gonna be amazing, this is gonna change my life,’” he says.

But Kipping, then a postdoc at Harvard University, also knew that his excitement might be clouding his judgment. Once he had talked himself into being more objective, he returned to his office. And after a few days, another astronomer helped him discover that the exomoon was nothing more than an artifact produced when the telescope vibrated a little. He was devastated.

Unfortunately, it wasn’t the only heartache of Kipping’s career — several exomoons have appeared on his computer screen before vanishing into thin air.

That appears to be a common trademark of alien satellites. Even the few candidates that have managed to make it onto the pages of prominent journals have remained evasive. Signs of a volcanically active exomoon might be easily explained away. The same is true for one possibly floating freely through space with its planet, as well as the satellite that might have carved a gap in the rings around a Saturn-like exoplanet. Even the best candidate, a Neptune-size