|  | Large waves rock regions of the magnetosphere | |
ESA's Cluster sees 'squashed' magnetosphere
31 October 2003
ESA's quartet of Cluster spacecraft joined in the flurry of interest in this week's extreme solar activity, and saw Earth's magnetosphere halved in size.
Cluster is a fleet of four spacecraft flying in formation around Earth. Their mission, lasting until 2005, is to complete the most detailed investigation ever made into the ways in which the Sun and Earth interact. They relay information about how the solar wind affects our planet in three dimensions.
Our planet is surrounded by a protective magnetic shield - the magnetosphere - that shelters the Earth from most of the charged particles that are blasted across interplanetary space by explosions on the Sun. The magnetosphere varies in size and shape, and its outer boundary - the magnetopause - gently undulates like a wave due to buffeting by the solar wind.
Because the four Cluster spacecraft have been positioned around the magnetopause since 2001, they have spent several years passing in and out of our planet's magnetosphere. Normally, at this time of year the spacecraft are inside the magnetopause.
However, this week, ESA's Cluster scientists saw a huge compression of the magnetosphere, which was squashed to about half of its usual size by the 'pressure' of the particles recently ejected by the Sun. These particles come from an earlier coronal mass ejection (CME) on the 24 October. The results from the event on the 28 October have yet to be seen.
All four Cluster spacecraft were out of the magnetosphere when they should have been inside. This is a very unusual position for the magnetopause, which on the average is projects outward from our planet to a distance equivalent to about 10 times the radius of the Earth.
Such compressions can have dramatic space weather effects, particularly to geostationary satellites which are orbiting the Earth at a distance of about six Earth radii.
Further analysis of the data from the four spacecraft will tell us at what speed the magnetopause moved which will give information on the strength of the CME.
Brought back to life...
As an interesting aside, there is some good news from the Cluster team. In contrast to the concerns about potential damage to satellites, one instrument on Cluster actually benefited from the solar storm.
A small component (an analogue-to-digital converter) that failed a few weeks ago was brought back to life. Although we can't be sure, the scientists think that this might have been due to interaction with the energetic particles from the Sun's outburst.
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