ESAs Cluster spacecrafts shocking experience in space

The European Space Agencys (ESAs) four spacecraft Cluster has encountered a shock wave that kept breaking and reforming, and has so far been predicted only in theory.

Paris, May 15 : The European Space Agency's (ESA's) four spacecraft 'Cluster' has encountered a shock wave that kept breaking and reforming, and has so far been predicted only in theory.

On January 24, 2001, the four Cluster spacecraft observed shock reformation in the Earth's magnetosphere.

That day, they were flying at an approximate altitude of 105 000 kilometres in tetrahedron formation. Each spacecraft was separated from the others by a distance of about 600 kilometres. With such a distance between them, as they approached the bow shock, scientists expected every spacecraft to record a similar signature of the passage through this region.

Instead, the readings they got were highly contradictory, and showed large fluctuations in the magnetic and electric field surrounding each spacecraft.

They also revealed marked variations in the number of solar wind protons that were reflected by the shock and streaming back to the Sun.

"The features derived from three different scientific experiments on the Cluster satellites provide the first convincing evidence in favour of the shock reformation model," said Vasili Lobzin of the Centre National de la Recherche Scientifique, Orl�ans, France, who headed this study.

Though predicted over 20 years ago by Vladimir Krasnoselskikh, also of the Centre National de la Recherche Scientifique, Orl�ans, France, and a collaborator on this new research, this is the first time that such a phenomenon has been observed.

According to the research team, the detection has implications for the way astronomers investigate larger bow shocks around distant celestial objects.

Bow shocks are related to some of the most energetic events in the Universe. Exploding stars and strong stellar winds from young stars cause them. This apart, reforming bow shocks can also accelerate particles to extremely high energies and throw them across space.

"Understanding the physics of shocks is essential for comprehending both complex astrophysical phenomena and accurately forecasts of the nearby space environment. Once again Cluster has demonstrated the need for formation flying with multiple spacecraft to augment our knowledge of shocks," said Philippe Escoubet, Cluster and Double Star project scientist at ESA.

The findings appear in a paper titled 'Nonstationarity and reformation of high-Mach-number quasiperpendicular shocks: Cluster observations' in the March 9, 2007 issue of the journal Geophysical Research Letters.

ANI