  High-precision pulsar timing relies on a solar-system ephemeris in order to
convert times of arrival (TOAs) of pulses measured at an observatory to the
solar system barycenter. Any error in the conversion to the barycentric TOAs
leads to a systematic variation in the observed timing residuals; specifically,
an incorrect planetary mass leads to a predominantly sinusoidal variation
having a period and phase associated with the planet's orbital motion about the
Sun. By using an array of pulsars (PSRs J0437-4715, J1744-1134, J1857+0943,
J1909-3744), the masses of the planetary systems from Mercury to Saturn have
been determined. These masses are consistent with the best-known masses
determined by spacecraft observations, with the mass of the Jovian system,
9.547921(2)E-4 Msun, being significantly more accurate than the mass determined
from the Pioneer and Voyager spacecraft, and consistent with but less accurate
than the value from the Galileo spacecraft. While spacecraft are likely to
produce the most accurate measurements for individual solar system bodies, the
pulsar technique is sensitive to planetary system masses and has the potential
to provide the most accurate values of these masses for some planets.
