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

We present measurements of the true masses and orbital inclinations of thetwo Earth-mass planets in the PSR B1257+12 system, based on the analysis oftheir mutual gravitational perturbations detectable as microsecond variationsof the arrival times of radio pulses from the pulsar. The 6.2-millisecondpulsar, PSR B1257+12, has been regularly timed with the Arecibo telescope sincelate 1990. Assuming the standard pulsar mass of 1.4 M_Sun, the derived massesof planets B and C are 4.3 +/- 0.2 M_Earth and 3.9 +/- 0.2 M_Earth,respectively. The corresponding orbital inclinations of 53.4 and 47.3 deg (or127 and 133 deg) imply that the two orbits are almost coplanar. This result,together with the known near 3:2 resonance between the orbits of the twoplanets, strongly supports the hypothesis of a disk origin of the PSR B1257+12planetary system. The system's long-term stability is guaranteed by the low,Earth-like masses of planets B and C.Comment: 2 figures, to appear in ApJ