Earth's outer core is composed essentially of liquid iron. At 2,900 kilometres below the surface, this vast liquid ocean makes up 16% of the planet's volume and conducts electricity. Motions in the core are what generate the planet's magnetic field.

This magnetic field is vital, since it shields us from the solar wind—a violent stream of gas and ionized particles flowing outward from the Sun.

Developed by Denmark, Oersted is the first satellite designed to fully measure Earth's magnetic field since the US Magsat satellite, launched in 1979. Its payload comprises two magnetometers measuring magnetic field intensity and direction, one of which is the French OVH instrument (OVerHauser).

Scientists worldwide have been using Oersted data since 1999. Combined with information from other sources, these data are supporting detailed study of the magnetic field and its variations—fundamental to develop a closer understanding of the globe's dynamics and motions inside the core. Thanks to Oersted, these motions have now been mapped for the first time, complementing calculations done with Magsat data 20 years earlier.

The satellite does not provide any more regular data since July 2006.

^{Last updated: August 2008}