Exoplanet hunters have found thousands of planets, most orbiting close to their host stars, but relatively few alien worlds have been detected that float freely through the galaxy as so-called rogue planets, not bound to any star. Many astronomers believe that these planets are more common than we know, but that our planet-finding techniques haven’t been up to the task of locating them.

Most exoplanets discovered to date were found because they produce slight dips in the observed light of their host stars as they pass across the star’s disk from our viewpoint. These events are called transits.

NASA.