THE BepiColombo spacecraft, a collaboration between the European Space Agency (ESA) and the Japan Space Agency (JAXA), successfully conducted its closest approach to the planet Mercury in early September 2024. This momentous occasion not only provided the first images of Mercury’s south pole, but also yielded important scientific data showing the rapid changes in the planet’s environment due to interactions with the solar wind.
On September 4, BepiColombo made its fourth successful flyby of Mercury. The mission aims to slow down the spacecraft to a closer approach to Mercury’s orbit in 2026. The team of scientists involved in the project, presenting their findings at the Europlanet Science Congress in Berlin, reported that 10 of BepiColombo’s 16 instruments have captured a wealth of interesting data about Mercury’s magnetic environment, which has been found to be highly variable and sometimes unpredictable.
Hayley Williamson, a senior scientist at the Swedish Institute for Space Physics and one of the SERENA BepiColombo instrument investigators, said that even though the spacecraft had passed through the same region on several previous flybys, the number of particles detected in the magnetosphere, the area affected by Mercury’s magnetic field, continued to vary. These changes reflect the dynamics of the planet’s environment.
In its fourth flyby, just 165 kilometers above Mercury’s surface, BepiColombo recorded for the first time Mercury’s ions—charged particles ejected from the planet’s surface by the solar wind. Interestingly, the particles were split into two different energy levels, which raised questions among scientists.
Overall, these data show that Mercury’s magnetic environment changes significantly with each flyby. This finding provides new insights into the interactions between the solar wind and our solar system’s smallest planet.
“Everything looks very different,” he said. “It really shows how dynamic the space environment on Mercury is.”
Also read: Mercury’s Smiling Face: BepiColombo’s Discovery of Stoddart Crater
The day before BepiColombo’s closest approach, a flurry of high-energy particles from the sun slammed into the spacecraft and Mercury. The particles dramatically affected the planet’s magnetosphere and could explain some unexpected features in the data, though more analysis is needed before drawing conclusions, Williamson said.
This latest flyby “is the closest a spacecraft has ever flown to a planet, including Earth,” said Ignacio Clerigo, who is BepiColombo spacecraft operations manager at the European Space Agency (ESA) in Germany.
He praised the flight control and mission dynamics teams for pulling off the complex rendezvous 21 miles (35 km) closer than planned. “This is truly an engineering achievement.”
Also read: Why Don’t Mercury and Venus Have Natural Satellites?
This close encounter with Mercury’s surface was caused by a revised trajectory by the mission team to address interference with the spacecraft’s propulsion system.
In April, engineers determined the electric thrusters on the spacecraft’s transfer module, which rely on electricity supplied by the module’s solar panels, were not operating at full power.
Anomalous electrical currents flowing between the spacecraft’s transfer module and the unit that distributes power to other parts of the spacecraft reduced the power available to the thrusters, prompting the team to create a revised route that required lower thrust levels.
Also read: Characteristics of the Eight Planets in Our Solar System
“It’s disappointing, but we have a simple solution,” Clerigo said. The revised route means BepiColombo will enter Mercury orbit in November 2026, 11 months behind schedule. The delay will not affect the mission’s science objectives, ESA said in a statement earlier this month.
The next milestone for the $1.8 billion spacecraft is a flyby of Mercury on December 1 and another on January 8, 2025 — three flybys in about four months.
“We have a very intense year ahead,” Clerigo said. (Space/Z-3)
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