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Cluster's new view of near-Earth space

16 February 2001

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The magnetosphere - a natural protective bubble

This image shows the main regions of the magnetosphere which are being studied by Cluster.

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Our planet is surrounded by a magnetic shield - the magnetosphere - which protects the Earth from most of the charged particles that are blasted across interplanetary space by explosions on the Sun. Artists' impression of the four Cluster spacecraft flying in tetrahedral formation in the vicinity of the magnetopause - the outer boundary of the magnetosphere. Here, one spacecraft (right) is still inside the magnetic field, one (centre) is at the undulating magnetopause and the other two have passed into interplanetary space. Events such as this will take place on a regular basis in 2001 and 2002. By comparing data from each member of the Cluster quartet, scientists are gathering the first detailed, three-dimensional views of one of the most important regions in the magnetosphere.

First results

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Data plots from the FGM instrument. Sharp decreases of the magnetic field on SC2 (red line) indicate crossing of the bow shock. The bow shock was first hovering very close to spacecraft 2 (06:50 to 07:03), then moved sunward of all four spacecraft (07:03 to 07:12). Later it stayed between spacecraft 2 and the other three spacecraft. Data courtesy of FGM Principal Investigator, Prof. Andre Balogh (Imperial College, London, UK)

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Data plots from the CIS instrument. These data plots from the CIS experiment on three Cluster spacecraft show the measured population of ions (charged particles) with energy from about 30 eV up to about 30 KeV between 07 and 17 GMT on 14 January 2001. The polar cusp was encountered between 13:30 and 13:50. Detailed comparison of the data on the different spacecraft indicates that the polar cusp was moving toward the Cluster spacecraft at a speed between 10 and 30 km/s. The motion of the cusp in relation to Cluster is shown on the left. Data courtesy of CIS Principal Investigator, Prof. Henri Reme and CIS Co-Investigator Jean-Michel Bosqued (CESR, Toulouse, France)

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Artists' impression of the Cluster spacecraft crossing the polar cusp. Particles from the solar wind precipitate through the polar cusp and reach the Earth's atmosphere.