Discovery of pulsar planets

In this paper I recount the events which have led to the discovery of the first planets beyond the Solar System. The two planets circling an old neutron star, the 6.2. ms pulsar PSR B1257+12, were discovered in 1991 with the 1000. ft Arecibo radio telescope. The pulsar itself was detected by a large, all-sky survey conducted during the telescope maintenance period in early 1990. The subsequent timing observations have shown that the only plausible explanation of the variability of pulse arrival times of PSR B1257+12 was the existence of at least two terrestrial-mass planets around it. The third, Moon-mass planet in the system was detected in 1994, along with the measurement of perturbations resulting from a near 3:2 mean motion resonance between the two more massive bodies, which has provided the confirmation of a planetary origin of the observed variations of pulse arrival times. Further observations and analyses have resulted in an unambiguous measurement of orbital inclinations and masses of the planets in 2003. The measured approximate coplanarity of the orbits along with the inner solar system - like dynamical properties of the pulsar planets strongly suggest their origin in a protoplanetary disk, just like in the case of planets around normal stars. The existence of such a system predicts that rocky, Earth-mass planets should be common around various kinds of stars.