Relativistic aspects of the JPL planetary ephemeris

The orbits of the planets as represented by the JPL planetary ephemerides are now primarily determined by radio tracking of spacecraft. Analysis of the data and propagation of the orbits relies on an internally consistent set of equations of motion and propagation of radio signals including relativistic effects at the centimeter level. The planetary ephemeris data set can be used to test some aspects of the underlying theory such as estimates of PPN parameters Y and (, time variation in the gravitational constant G, rotation of the solar system relative to distant objects (Machʹs principle), and place stringent limits on the possible violation of the inverse-square law.