The joint European-Japanese BepiColombo spacecraft captured high-resolution images and particle data during its fourth Mercury flyby, passing 103 miles above the surface. The September 2024 maneuver also provided key insights into space weather after a solar eruption hurled high-energy particles directly at the innermost planet.
Eight years after launching into space in October 2018, the BepiColombo mission is finally locking into its operational geometry around the solar system’s innermost world. The journey has demanded complex gravity assists and rigorous braking maneuvers because spacecraft naturally pick up speed as they near the massive sun. To shave off velocity, the probe has relied on flybys of Earth, Venus, and its ultimate destination.
While the mission encountered propulsion setbacks that pushed its definitive arrival date out, the intermediate passes have yielded extraordinary science. During the fourth flyby, the spacecraft swooped just 165 kilometers above Mercury’s rugged crust. That close approach coincided precisely with a major particle eruption on the Sun, offering researchers a look at how an unprotected planetary body reacts to violent solar bombardment.
Capturing Vivaldi, Stoddart, and Mercury’s Volcanic Past
The close encounter delivered some of the sharpest visual data of the mission so far, utilizing BepiColombo’s monitoring cameras to map heavily cratered terrain. Among the prominent features highlighted in the imaging runs are the Vivaldi impact basin—named for the Italian composer Antonio Vivaldi—and the newly designated Stoddart crater, named after New Zealand artist Margaret Olrog Stoddart.
Both geological formations display distinct peak ring basins, which are created by large asteroid or comet impacts. The imagery helps untangle the complex formation history of these mountain rings, which researchers believe are resulted from some kind of rebound process following an impact. In the Vivaldi basin, cameras revealed a visible gap in the ring of peaks where more recent lava flows entered and flooded the structure.
“Mercury’s peak ring basins are fascinating because many aspects of how they formed are currently still a mystery. The rings of peaks are presumed to have resulted from some kind of rebound process during the impact, but the depths from which they were uplifted are still unclear.”
David Rothery, professor of Planetary Geosciences at the U.K.’s Open University and a member of the M-CAM imaging team
Researchers note that the planet remains uniquely difficult to categorize. Jack Wright, an ESA research fellow and planetary scientist, previously dubbed the world the Problem Child of the Solar System
due to its abundance of geological extremes and contradictions.
Studying Solar Storms and Particle Bombardment at Mercury
Beyond photography, the Solar Intensity X-ray and Particles Spectrometer, or SIXS, seized a rare scientific opportunity. Developed by engineers and technicians at the University of Helsinki, the instrument recorded how high-energy electrons and protons accelerated by a solar eruption rained across Mercury’s wide surface area.
Because Mercury lacks a substantial atmosphere to protect it, these energetic charged particles smashed directly into surface atoms and molecules, generating X-ray radiation in the process. These interactions provide insights into the planet’s surface composition and evolutionary history.
“The fourth flyby was truly unique, and the spacecraft came much closer to the surface than it will be on its final orbit, and we were lucky that a major particle eruption occurred on the Sun at exactly that moment.”
Emilia K. J. Kilpua, professor of space physics at the University of Helsinki and Principal Investigator for SIXS
The data collected during the flyby also sheds light on how rocky bodies withstand stellar weather. Because Mercury possesses an intrinsic magnetic field that is much weaker and smaller than Earth’s, the compression of its magnetosphere during a solar storm mimics what happens closer to home during powerful space storms.
According to Rami Vainio, co-principal investigator of SIXS and a professor of space physics at the University of Turku, these observations help scientists assess how destructive particle radiation penetrates near-space environments and atmospheres. Those insights directly feed into broader research initiatives, including the Center of Excellence in Space Resilience, which works to ensure that commercial and scientific operations in Low Earth Orbit remain safe under the most extreme space weather conditions.
Orbital Insertion Timeline and Separation Steps
The mission reached another major logistical milestone when the Mercury Transfer Module successfully separated from the two primary science orbiters. The spacecraft propulsion unit detached to leave the Mercury Planetary Orbiter and the Mercury Magnetospheric Orbiter on their final approach.
The structural separation follows an adjusted trajectory designed by European Space Agency teams after a propulsion system issue reduced thruster power. Originally scheduled to settle into orbit in December 2025, the spacecraft is now on course to complete its arrival sequence.
- September 3, 2026: The Mercury Transfer Module successfully separated from the two science orbiters.
- November 21, 2026: The twin spacecraft are scheduled to enter orbit around Mercury.
- December 9–10, 2026: The Mercury Planetary Orbiter and the Mercury Magnetospheric Orbiter will separate from each other.
- April 2027: Full science operations are scheduled to officially commence.
Once the two orbiters separate in December, they will spend at least a year utilizing their combined suite of 16 scientific instruments to map the surface, search for polar ice, and monitor the shifting boundaries of the planet’s magnetosphere.
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