Simulation of Mercury’s magnetic environment

When we look at BepiColombo’s images of Mercury, it can seem like the space around the planet is empty. But in fact, it is teeming with particles – neutral and charged, energetic and sluggish. 

Mercury has a magnetic field that interacts with particles from the Sun (the ‘solar wind’). This creates Mercury’s magnetosphere – a bubble in space that is shaped like a windsock extending away from the Sun. This bubble is constantly changing in response to the solar wind. 

This output from a simulation shows an expected case of Mercury’s magnetic environment under typical solar wind conditions. The left image shows a ‘side view’ where the Sun is out of frame to the left; the right image shows a ‘front view’ as if we are looking at Mercury from the direction of the Sun. The simulation is based on a model, it does not show real observations.  

The colours indicate the density of charged particles around Mercury, with the highest density shown in yellow and the lowest density in purple/black. The white lines are magnetic field lines. (The near-vertical lines extending from the planet’s poles are numerical artefacts and should be ignored.)  

The undisturbed solar wind appears dark orange. As the solar wind meets Mercury’s magnetic field, it is heated and deflected, creating a denser region of solar wind particles shown in yellow. Inside this dense layer, we see that the number of solar wind particles very quickly drops to almost zero, except for a stream extending from the equator. 

Studying Mercury’s magnetosphere with BepiColombo deepens our understanding of how these bubbles function. Most of our current knowledge of magnetospheres is based on observations of the much more stable magnetic environments of Earth, Jupiter and Saturn. At Mercury, the solar wind is ten times stronger than at Earth, and much more variable. Meanwhile, Mercury’s internal magnetic field is 2000 times weaker than Earth’s. This results in a tiny, highly changeable magnetosphere that persists despite lacking several components thought to be key to magnetosphere stability.  

BepiColombo will study Mercury’s magnetic environment in greater detail than ever once its two spacecraft – ESA’s Mercury Planetary Orbiter and JAXA’s Mercury Magnetospheric Orbiter – are in complementary orbits around the planet (starting late 2026). Their instruments are also activated during the flybys of Mercury, collecting unique data in this dynamic environment. 

Click here for an animated simulation