When the BepiColombo Mercury probe made its closest approach yet to its target earlier this month, the spacecraft not only captured the first clear view of the planet's south pole but also collected valuable science data that underscores just how sharply and rapidly its local environment changes in response to the solar wind.

On September 4, BepiColombo conducted its fourth successful swing past Mercury. This flyby reduced the European-Japanese probe's speed and altered its direction, taking it a step closer to entering orbit around the planet in 2026. A preliminary analysis of data collected by 10 of the spacecraft's 16 instruments indicates that the environment around Mercury varies significantly, showcasing occasionally unexpected features. Mission team members presented these findings last week at the Europlanet Science Congress in Berlin.

Flyby Insights and Variability

Although BepiColombo flew through the same regions around Mercury during each of the previous three flybys, the probe's instruments recorded varying counts of particles in the bubble-like magnetosphere carved out by the planet's magnetic field. Hayley Williamson, a senior scientist at the Swedish Institute for Space Physics and a co-investigator on BepiColombo's SERENA instrument, noted that this variability highlighted the dynamic nature of Mercury's space environment.

During the latest flyby, which took BepiColombo just 103 miles (165 kilometers) above Mercury's surface, the probe recorded planetary ions for the first time. These charged particles waft in Mercury's magnetosphere after being blasted from its surface by the solar wind. Notably, those particles appeared to split into two different energy levels shortly after BepiColombo's closest approach, suggesting alterations in the magnetic environment surrounding Mercury.

"They all look quite different," Williamson commented. "It really shows just how dynamic Mercury's space environment is." This reinforces the importance of continuous monitoring and assessment as the mission progresses.

The Role of Solar Activity

Just a day before BepiColombo's latest close approach, a pocket of high-energy particles from the sun impacted both the spacecraft and Mercury. Such solar activity would have dramatically influenced the planet's magnetosphere and may account for some unexpected features observed in the data collected. However, Williamson cautioned that further analysis is essential before drawing any definitive conclusions regarding these observations.

The latest flyby marked a historical achievement. Ignacio Clerigo, BepiColombo's spacecraft operations manager at the European Space Agency (ESA) in Germany, stated, "This was the closest a spacecraft has ever flown by a planet, including Earth." He credited the mission's flight control and dynamics teams for successfully executing the complex encounter, which was 21 miles (35 km