At exactly 08:45:40 Central European Time, Rosetta passed over the Pacific Ocean south of the Indonesian island of Java, according to the European Space Agency (ESA). "The swingby was pre-planned and fully automated, and the spacecraft was in direct communication with Earth at the time," ESA said.

In the swingby, the billion-euro ($1.5 billion) Rosetta sped past the Earth at 13.3 kilometers (8.3 miles) per second. The slingshot effect allowed Rosetta to accelerate by 3.6 kilometers per second. In 1990 scientists noticed that, with such a gravity assist, spacecraft get an unexpected acceleration of just a few millimeters per second that Einstein's theory of relativity does not account for. They're hoping this latest flyby will shed more light on whether the Earth's rotation could be distorting the fabric of "space-time" more than previously thought.

"It's a mystery as to what is happening with these gravity events," said Trevor Morley, the lead flight dynamics specialist for Rosetta's mission control in Darmstadt, Germany.

"Some studies have looked for answers in new interpretations of current physics. If this proves correct, it would be absolutely ground-breaking news," he added.

Once the Rosetta reaches Comet 67P/Churyumov-Gerasimenko in May 2012 it will send down a laboratory, Philae, which will anchor itself to the surface of the comet. There it will look for clues from its composition indicating how comets and planets were formed in the early days of the Solar System.

hf/AFP/dpa
Editor: Susan Houlton