Every now and then, a distant star called KIC 8462852 dims by as much as 20 percent. That’s huge. Even a passing planet as big as Jupiter would only block about 1 percent of the star’s light.
Ruling out a planet, scientists have no idea what could be eclipsing the star (which is informally known as ‘Tabby’s Star’). The leading hypothesis is a family of really big comets, but that doesn’t quite fit.