The Bad Astronomer writes "Exoplanets orbiting binary stars have been discovered before, but NN Serpentis is a weird system even in that category. One star is a red dwarf in an incredibly tight orbit around a white dwarf. The white dwarf used to be a star like the Sun but became a red giant as it died, engulfing the red dwarf. Now the two orbit each other almost as closely as the Moon orbits the Earth. Explaining how the two newly detected exoplanets survived such an event is very difficult, and astronomers think they may have actually formed from the material expelled by the star as it died."