Astrophys. J. 720, L201–L205 (2010)

Accurate weights for nearby planets have been calculated from observations of the effect their gravity has on passing spacecraft. But that requires a spacecraft and gives the mass of only a planet, not the planet and its moons.

David Champion of the Australia Telescope National Facility in Epping, New South Wales, and his colleagues show that radio pulses emitted by a type of neutron star called a pulsar can provide similar information. Shifts in the alignment of masses in the Solar System affect the arrival times of these pulses at observatories. Using at least ten years' worth of measurements, and focusing on variations in signals from four pulsars, the authors were able to measure the masses of all of the planets (plus moons), except Uranus and Neptune, at up to seven-decimal accuracy — comparable to the best results from spacecraft fly-bys. With another ten years' worth of data, they hope to refine that even further.