Why do spacecraft speed up near Earth?

Our planet gives spacecraft a buzz of energy – but why?

ESA’s Rosetta spacecraft gets a buzz of energy from our planet

ESA’s Rosetta spacecraft gets a buzz of energy from our planet

When spacecraft pass the Earth, they get a buzz from it and this sudden boost makes them speed up. But what’s causing it? The answer is that nobody seems to know. Even researchers at NASA’s Jet Propulsion Laboratory have thrown up their hands, hoping that the world’s physicists would come up with an answer. That solution doesn’t seem to have arrived yet, although we’ve come to expect what we refer to as the flyby anomaly.

It first happened when the Jupiter-bound Galileo spacecraft broke into a sprint when it swung by our planet in 1990 and 1992, followed by NEAR in early 1998 and then Cassini in 1999. The Rosetta spacecraft, which  reached its destination at comet 67P/Churyumov–Gerasimenko, also experienced the same boost back in 2005. All crafts were using the Earth’s gravitational assistance to catapult themselves into the Solar System.

The most obvious boost in speed, which changed a good 13 millimetres per second more, was recorded for the Near Earth Asteroid Rendezvous – Shoemaker (NEAR Shoemaker) spacecraft. Scientists figured that the anomaly was much too big to be explained by Einstein’s general theory of relativity. However, arming themselves with a variety of suggestions, some experts think that they might have the answer. Perhaps, they investigate, that the anomaly could be due to the Earth’s spin on its axis, or there could be some type of dark matter halo around our planet. The possibilities are coming, but we need to choose the one that fully fits.

Image Credit: ESA

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