Over the past ten years the satellites have provided an exceptional insight into the largely invisible interaction between the Sun and Earth
The Cluster mission got underway in summer 2000 with the launch of two Russian Soyuz rockets which each took two identical satellites into orbit from the Baikonur Cosmodrome in Kazakhstan. Since then the four satellites of identical design have been testing the effects of the solar wind on the Earth’s magnetic field. Over the past ten years they have provided an exceptional insight into the largely invisible interaction between the Sun and Earth.
Originally the four Cluster satellites were to be put into orbit during the maiden flight of the Ariane 5 rocket in June 1996, but the launch failed. On resumption of the unique Cluster project Airbus Defence and Space was appointed as prime contractor for the development and production of the replica version.
The four Cluster satellites, Rumba, Samba, Salsa and Tango, orbit the Earth in tetrahedron formation. This formation makes it possible to produce a three-dimensional image of how the continuous solar wind, consisting of charged particles or plasma, influences our near-Earth space environment and its protective ‘magnetic bubble’, known as the magnetosphere.
Over the past decade the Cluster II mission has provided us with a wealth of data, enabling a better understanding of the physical processes at play in “space weather”. Cluster has revealed the extreme strength of invisible forces which the plasma exerts on our magnetosphere. The mission has studied how the solar winds penetrate the outer layers of the Earth’s atmosphere. It was discovered that under certain circumstances magnetic whirpools larger than the entire Earth bore into our magnetosphere, injecting their harmful particles. When these solar wind particles reach the Earth’s atmosphere they trigger the sublime glow of the Northern and Southern Lights. Here, too, Cluster has revealed the underlying physical events.
Undoubtedly, one of the main highlights of the mission is the first 3D map of the heart of a ubiquitous magnetic process called reconnection. This takes place when magnetic fields collide, releasing energy and enabling previously separated plasmas of electrified gas to mix. Right at the centre of this phenomenon is the ‘null point’. Cluster has delivered the first 3D map of these null points, providing important new information to scientists. During the reconnection event, the magnetic field is twisted into a 500 km-wide tube.
Understanding magnetic reconnection is a major quest in physics. It is responsible for solar flares, enormous solar explosions which can be a billion times more powerful than an atom bomb.
The Cluster Mission represents a major milestone in gaining an insight into space weather and is helping scientists to understand how plasma behaves in different environments. As the four satellites are still in excellent condition, the mission has been extended until 2012.