Asked by John Garnet
Philae – the robotic lander of the European Space Agency’s Rosetta probe – was dropped on to Comet 67P/Churyumov-Gerasimenko in November. However, the manoeuvre hasn’t changed the orbit of the comet.
There are two reasons why this is not possible. The first is that when Rosetta entered into orbit around the comet in August 2014, the pair became gravitationally bound. The comet lost a little bit of angular momentum – the amount of rotation that it had – to Rosetta and if the comet were to be perturbed at all, it would have happened at this point. Second, Rosetta is 1,230 kilograms (2,712 pounds) while Philae is a mere 100 kilograms (220 pounds). Compared to the comet, which has a mass of ten billion tons, they are very light and unable to knock the comet out of its stride.
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