The BepiColombo mission, a collaboration between the European Space Agency (ESA) and the Japan Aerospace Exploration Agency (JAXA), successfully completed its fourth gravity assist flyby of Mercury on September 4, 2024.
Navigating Mercury’s Gravity: A Critical Maneuver
BepiColombo’s fourth flyby was a key moment in its complex journey toward Mercury’s orbit. The spacecraft is currently using a series of gravity assist flybys to gradually adjust its speed and path, relying on Mercury’s gravitational pull to slow down relative to the Sun. According to Frank Budnik, Flight Dynamics Manager for the BepiColombo mission, "The main aim of the flyby was to reduce BepiColombo’s speed relative to the Sun, so that the spacecraft has an orbital period around the Sun of 88 days, very close to the orbital period of Mercury." These flybys are essential for aligning BepiColombo’s orbit with that of Mercury, a feat that requires precise navigation and a deep understanding of orbital mechanics.
The spacecraft came incredibly close to the planet—just 165 kilometers above its surface—passing over Mercury’s nightside to minimize the risk posed by extreme heat from the Sun. This close approach not only achieved the necessary orbital changes but also provided the mission team with an opportunity to capture stunning images of Mercury's surface. The mission's three monitoring cameras snapped photos as the planet’s cratered surface gradually emerged into sunlight, offering detailed views of craters and geological features that had never been seen at such close range before.
Stunning New Images: Unveiling Mercury’s Surface
Although BepiColombo’s monitoring cameras were not designed for scientific imaging, they delivered some of the most detailed images yet of Mercury’s southern hemisphere. The spacecraft’s cameras captured breathtaking views of the planet’s cratered terrain, which was illuminated as BepiColombo passed from the dark side into daylight. These images highlighted some of Mercury’s most intriguing geological features, including the Vivaldi crater, a 210-kilometer-wide impact crater named after the famed Italian composer. Seen in the low-angle light near Mercury's sunrise, the crater’s central peaks and ringed walls were beautifully emphasized by the shadows cast across its floor.
Another standout feature from the flyby was the newly named Stoddart crater, which spans 155 kilometers. Named after Margaret Olrog Stoddart, a renowned New Zealand artist, this crater is of particular interest to planetary scientists due to its well-preserved structure. "Mercury’s peak ring basins are fascinating because many aspects of how they formed are currently still a mystery," explained David Rothery, a planetary scientist and member of the BepiColombo imaging team. The Stoddart crater, like others on Mercury, shows signs of volcanic activity, with lava flows filling much of its floor, adding to the planet’s complex geological history.
Preparing for BepiColombo’s Main Science Phase
The images captured during this flyby are just a glimpse of what BepiColombo will be able to accomplish once it enters Mercury’s orbit in 2026. While the monitoring cameras provide detailed, black-and-white images, BepiColombo’s main science camera will offer much higher-resolution, color images once the spacecraft reaches its final orbital position. In addition to high-resolution imaging, the mission will deploy a comprehensive suite of scientific instruments designed to study Mercury’s magnetic field, surface composition, and geological evolution.
BepiColombo's primary science mission is set to begin in 2027, after its two scientific orbiters—ESA’s Mercury Planetary Orbiter and JAXA’s Mercury Magnetospheric Orbiter—are deployed. These orbiters will work together to explore Mercury’s interior, surface, and surrounding magnetic environment. "The images and science data collected during the flybys offer a tantalizing prelude to BepiColombo's orbital phase," said Jack Wright, ESA Research Fellow and planetary scientist. "Once in orbit, BepiColombo will help solve Mercury's outstanding mysteries, from its origins to its extreme environment."
Next Steps: Future Flybys and Mission Objectives
BepiColombo’s journey to Mercury is far from over. The spacecraft has two more gravity assist flybys scheduled for December 2024 and January 2025, each one bringing the mission closer to its target orbital insertion. These flybys are crucial for fine-tuning BepiColombo’s trajectory, ensuring that the spacecraft can smoothly transition into its final orbit around Mercury by November 2026.
Mercury has long been one of the least-explored planets in the inner solar system, largely due to its proximity to the Sun and the complexities of reaching it. With only two previous missions—NASA’s Mariner 10 and Messenger—having visited the planet, BepiColombo represents a major opportunity to gain new insights into this enigmatic world. Once the mission reaches its full operational capacity, it is expected to shed light on fundamental questions about Mercury’s formation, magnetic field, and its place in the evolution of the solar system.
As BepiColombo continues its journey, each flyby brings new data and images that offer a deeper understanding of Mercury’s mysteries, while also preparing the spacecraft for the comprehensive scientific studies that will begin once it settles into orbit.