Toward planets around neutron stars

The two Earth-like mass objects orbiting a 6.2-ms pulsar, PSR1257+25, have survived more than one year of close scrutiny aimed at verifying their existence and remain the most serious candidates to become the first planets detected beyond the Solar System. The analysis of systematic timing measurements of the pulsar made over a 2.5-year period continues to require the presence of two planets with the minimum masses of 3.4 M_⊕ and 2.8 M_⊕ and the corresponding distances from PSR1257+12 of 0.36 AU and 0.47 AU to correctly predict the pulse arrival times. The presently available 3 μs rms accuracy of this procedure leaves little room for significant contributions to the pulsar's timing from any mechanisms other than the Keplerian motion. A detection of the effect of planetary perturbations on pulse arrival times which is commonly accepted as the most convincing way to furnish a "100% proof" of the reality of pulsar planets is already possible at a ∼ 2σ level. Intensive searches for millisecond pulsars now under way at various observatories are expected to address a very intriguing question of the frequency of occurrence of neutron star planetary systems.