Structure, force balance, and topology of Earth’s magnetopause

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Science  02 Jun 2017:
Vol. 356, Issue 6341, pp. 960-963
DOI: 10.1126/science.aag3112

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Probing the structure of the magnetopause

The magnetopause is the boundary in space that separates the region dominated by Earth’s magnetic field (the magnetosphere) from the surrounding solar wind. The four spacecraft of NASA’s Magnetospheric Multiscale (MMS) mission have repeatedly flown in formation through the magnetopause, measuring the properties of the plasma and magnetic fields in the region. Russell et al. used MMS measurements to study the magnetopause’s structure and force balance. They identified small-scale dynamic features that form a complex topology and evidence for magnetic flux ropes at the boundary. The results aid our understanding of Earth’s space environment and magnetospheres around other planets.

Science, this issue p. 960


The magnetopause deflects the solar wind plasma and confines Earth’s magnetic field. We combine measurements made by the four spacecraft of the Magnetospheric Multiscale mission to demonstrate how the plasma and magnetic forces at the boundary affect the interaction between the shocked solar wind and Earth’s magnetosphere. We compare these forces with the plasma pressure and examine the electron distribution function. We find that the magnetopause has sublayers with thickness comparable to the ion scale. Small pockets of low magnetic field strength, small radius of curvature, and high electric current mark the electron diffusion region. The flow of electrons, parallel and antiparallel to the magnetic field, reveals a complex topology with the creation of magnetic ropes at the boundary.

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