For the first time, astronomers claim to have developed a new way to weigh the planets in our solar system — using radio signals from the highly magnetised small spinning stars known as pulsars. Observations of a set of four of these pulsars, were used to calculate the masses of Mercury, Venus, Mars, Jupiter and Saturn, including their moons, says an international team led by Germany's Max Planck Institut für Radioastronomie. "This is first time anyone has weighed entire planetary systems — planets with their moons and rings. And, we have provided an independent check on previous results, which is great for planetary science," team leader Dr David Champion said. Until now, planetary scientists have weighed planets by measuring the orbits of their moons or of spacecraft flying past them. That's because mass creates gravity, and a planet's gravitational pull determines the orbit of anything around it — the orbit's size and how long it takes to complete. The new technique is quite precise sensitive to about 0.003 per cent of Earth's mass, and a tenth of a millionth of Jupiter's mass. And in the future combining pulsar timing with existing data sets will lead to even greater precision, the astronomers say. In fact, the new method is based on corrections the astronomers make to signals from pulsars — small spinning stars that deliver regular "blips" of radio waves.