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.

In this simulation, we see the path that BepiColombo will take around Mercury during the spacecraft’s fourth gravity assist flyby of the planet on 4 September 2024.

Studying Mercury’s magnetic environment with BepiColombo is helping us understand how a planet responds to its host star when it is so close to it. At Mercury, the solar wind is ten times stronger than that at Earth. However, Mercury’s internal magnetic field is 2000 times weaker than Earth’s. This results in a very open and variable magnetosphere that can change significantly within just a few minutes.

This simulation shows an expected case of Mercury’s magnetic environment under typical solar wind conditions. The colours indicate the density of solar wind particles around Mercury, with the highest density shown in yellow and the lowest in purple/black. In the first half of the video, we see a ‘side view’ where the Sun is out of frame to the left; in the second half we see 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 undisturbed solar wind is shown in dark orange. As the solar wind meets Mercury’s magnetic field, it is heated and deflected, creating a region full of solar wind particles shown in a lighter yellow/orange. Inside this dense layer, we see that the number of solar wind particles very quickly drops to almost zero, except for a low-density stream extending from the equator.

During BepiColombo’s first three Mercury flybys, its onboard instruments measured big differences as it crossed the planet’s magnetosphere. The fourth flyby will take BepiColombo on its closest approach to Mercury yet, as well as on its first pass over the planet’s poles.

Before, during and after the fourth flyby, various instruments onboard BepiColombo will collect data on magnetic and electric field strength, as well as measuring the particles around Mercury, revealing totally new information about the planet’s magnetic environment.

We will be sharing some of this information via esa.int/bepicolombo and @BepiColomboafter the flyby, and seeing how our simulations compare to the real data!

Access the related broadcast quality footage.