Inside Rosetta’s comet
Pätzold’s team made their discovery by using the Radio Science Experiment (RSI) to study the way the Rosetta orbiter is pulled by the gravity of the comet, which is generated by its mass. The effect of the gravity on the movement of Rosetta is measured by changes in the frequency of the spacecraft’s signals when they are received at Earth. At 10 km and above, only the total mass would be measurable. Then the comet’s strange shape was revealed as Rosetta drew nearer. “We were already seeing variations in the gravity field from 30 km away,” says Pätzold.