A cartoon showing a typical magnetic cloud in the heliosphere. The inner purple field line is more twisted than other two outer lines in the magnetic cloud. The reconnection site implies the erosion process. Credit: Wang et al., 2018, Figure 11
Source: Journal of Geophysical Research: Space Physics

The Sun regularly launches material and magnetism into the solar system, and occasionally the structure of these disturbances is neatly coiled into a magnetic flux rope. These are not static structures, and definitely not stationary—moving at supersonic speeds of hundreds of kilometers per second, they barrel their way through the ambient, often slower, solar wind that permeates interplanetary space. We have lots of observations of these flux ropes, but mostly from single spacecraft near Earth, making a study of the temporal evolution of these phenomena a rare and difficult study to undertake. That is, there are very few measurements in good radial alignment through the solar system.

Wang et al. [2018] take full advantage of a good planetary configuration to investigate the twist and deformation of a magnetic structure (ejected from the sun after a solar flare) propagating through the solar system. An interesting new finding is that while the magnetic field strength decreases with distance from the Sun, the twist (turns of the field per cross sectional width of the magnetic flux rope) increases with this distance. They find that two things happen to the flux rope during its flight through the inner solar system: it gets radially compressed, shrinking the cross-sectional width; and it gets eroded, losing the low-twist part on the outer edges. This could only be discovered with this analysis of a chain of satellites spread throughout the inner solar system (at Mercury, Venus, Earth, and Mars).

Wang, Y., Shen, C., Liu, R., Liu, J., Guo, J., Li, X., et al. [2018]. Understanding the twist distribution inside magnetic flux ropes by anatomizing an interplanetary magnetic cloud. Journal of Geophysical Research: Space Physics, 123. https://doi.org/10.1002/2017JA024971

—Mike Liemohn, Editor-in-Chief, JGR: Space Physics

Text © 2018. The authors. CC BY-NC-ND 3.0
Except where otherwise noted, images are subject to copyright. Any reuse without express permission from the copyright owner is prohibited.