"Most people are taught at school that the acceleration due to gravity at the Earth's surface is 9.8m per second squared - but, in truth, this figure varies around the planet depending on the nature of the material underfoot."

"By combining the gravity data with information about sea-surface height gathered by other spacecraft, scientists will be able to track the direction and speed of ocean currents.

"If we want to improve our climate models then we need to improve our knowledge of how the oceans move, and Goce will help us do that," mission scientist Dr Mark Drinkwater, from the European Space Agency (Esa), told BBC News. "