Scientists discovered two planets orbiting the pulsar PSR B1257+12 in 1992, t A pulsar is a highly magnetised rotating neutron star, a massive dead star with a typical size of only about 20 km. Pulsars emit strong electromagnetic radiation from their poles. Just like a lighthouse, we only see the beam when it is pointed at us. The rotation time of such a star is very precise but when scientists measured the time between beams for PSR B1257+12 they found a deviation, which they linked to the presence of two planets around the star. Later, a third planet was discovered.