Simulations of the global magnetic environment of Mercury that reproduce recent observations from the NASA MESSENGER missions are presented in Nature Communications this week. The simulations mimic the asymmetry of vortices seen in the magnetosphere and present an explanation for it.

NASA’s MESSENGER missions to Mercury are revealing a great deal of new information on the behaviour this planet’s atmosphere, including the magnetic layer known as the magnetosphere. Among the findings is the presence of large-scale vortices on the dusk side of the planet. Jan Paral and Robert Rankin develop simulations that encompass the magnetosphere of the whole of Mercury in order to explain this asymmetry. They find that they can reproduce the MESSENGER observations, mimicking the Kelvin-Helmholtz instabilities - a type of instability occurring in fluids such as plasmas - and their development across the magnetosphere. Their model shows that this instability produces the vortices and that the overall asymmetry in the magnetosphere is controlled by the different motion of ions on either face of Mercury.

When compared with the behaviour of Earth’s magnetosphere, the results here highlight important differences connected with the relative size of the magnetic environments. The authors suggest that the simulations could be applied to other planetary magnetospheres, which will help in further assessing these differences.