ESA's magnetic field mission Swarm   Swarm constellation of three satellites   Swarm is an Earth Explorer Opportunity Mission. The Swarm constellation will study the dynamics of the Earth's magnetic field and its interactions with the Earth system. Each Swarm satellite will be eight metres long and weigh 300 - 400 kilograms.   The Earth's magnetic field is mainly produced by a self-sustaining dynamo in the fluid outer-core. Last update: 27 October 2011