Research Highlights

Magnetic reconnection: From null to null

Subject Categories: Physics, Space & astronomy

Published online 4 July 2007


The Cluster space mission has detected the geometry of the line that connects two magnetic nulls

Felix Cheung

© (2007) Nature Phys.

On the night side of the magnetosphere, there is a region where complex magnetic field lines are constantly changing (pictured). In 2006, an international team of scientists led by Chijie Xiao at the Chinese Academy of Science and Zuyin Pu at Peking University, both in Beijing, identified a magnetic null — a point in space at which magnetic field lines break and reconnect1. Now, they have not only found a pair of magnetic nulls, but also the line that connects them2.

The researchers analysed data from Cluster, an unmanned space mission launched by the European Space Agency (ESA) in 2000. Cluster uses four identical spacecrafts flying in a tetrahedral formation to study the Earth's magnetic environment, or magnetosphere.

During an event in 2001, the Cluster tetrahedron was able to circle around the magnetic reconnection region several times. Based on four-second-average data of the magnetic field, plasma density and velocity, collected by the spacecraft, the Cluster tetrahedron was observed to have encountered the 'X-line', where magnetic nulls could be detected.

The researchers used the Poincaré index method, which had successfully detected a magnetic null previously1, and identified a magnetic-null pair. They were able to determine the alignment of the null-to-null line and the length, about 860 km.

The authors of this work are from:
National Astronomical Observatories, Chinese Academy of Sciences, Beijing, China; School of Physics, Peking University, Beijing, China; State Key Lab of Materials Modification by Beams, Dalian University of Technology, Dalian, China; School of Earth and Space Sciences, Peking University, Beijing, China; Institute for Fusion Theory and Simulation, Zhejiang University, Hangzhou, China; Institute of Plasma Physics, Chinese Academy of Sciences, Hefei, China; Institute of Geophysics and Planetary Physics, University of California, Los Angeles, California, USA; CSSAR, Chinese Academy of Sciences, Beijing, China; Center for Atmospheric Research, University of Massachusetts Lowell, Lowell, Massachusetts, USA; Space Sciences Division, SSTD, Rutherford Appleton Laboratory, Chilton, UK; IGEP, Technische Universität Braunschweig, Braunschweig, Germany; Blackett Laboratory, Imperial College, London, UK; Centre d'Etude Spatiale des Rayonnements, Toulouse, France; ESA/ESTEC, Noordwijk, The Netherlands.


  1. Xiao, C. J. et al. In situ evidence for the structure of the magnetic null in a 3D reconnection event in the Earth's magnetotail. Nature Phys. 2, 478–483 (2006). 10.1038/nphys342  | Article | ISI | 
  2. Xiao, C. J. et al. Satellite observations of separator-line geometry of three-dimensional magnetic reconnection. Nature Phys. doi: 10.1038/nphys650 (2007).  | Article |