Astronomers are puzzling over some space oddities: planets that don’t orbit stars. In “Wandering worlds” (SN: 4/4/15, p. 22), Ashley Yeager explored how these lonely rogues may alter the definition of a planet.
Tim Geho wanted to know more about how scientists locate homeless worlds. “Where does the light come from that allows rogue planets to be seen, either directly or via gravitational lensing?” he asked. “Is there some sort of fluorescence or luminescence involved or is [light] reflected from distant suns?”
Some rogues can be imaged directly because big planets can emit their own heat, Yeager