Masses and Orbital Inclinations of Planets in the PSR B1257+12 System

We present measurements of the true masses and orbital inclinations of the two Earth-mass planets in the PSR B1257+12 system, based on the analysis of their mutual gravitational perturbations detectable as microsecond variations of the arrival times of radio pulses from the pulsar. The 6.2 ms pulsar, PSR B1257+12, has been regularly timed with the Arecibo telescope since late 1990. Assuming the standard pulsar mass of 1.4 M_☉, the derived masses of planets B and C are 4.3 ± 0.2 and 3.9 ± 0.2 M_⊕, respectively. The corresponding orbital inclinations of 53° ± 4° and 47° ± 3° (or 127° and 133°) imply that the two orbits are almost coplanar. This result, together with the known near 3 : 2 resonance between the orbits of the two planets, strongly supports the hypothesis of a disk origin of the PSR B1257+12 planetary system. The system's long-term stability is guaranteed by the low Earth-like masses of planets B and C.