The ESA/JAXA BepiColombo mission has successfully executed its fourth of six gravity assist flybys at Mercury, securing vital data and images from two notable impact craters. These flybys utilize the gravitational influence of Mercury to guide the spacecraft toward its final destination in orbit around the planet, set for November 2026.

Closest Approach and Observation

On September 4, 2024, at 23:48 CEST (21:48 UTC), BepiColombo made its closest approach to Mercury, coming within 165 km of the planet's surface. This significant event marked the first opportunity for the spacecraft to observe Mercury's south pole clearly.

Frank Budnik, the BepiColombo Flight Dynamics Manager, noted, "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. In this regard, it was a huge success, and we are right where we wanted to be at this moment." He also emphasized the scientific value of this flyby, stating that it allowed for photography and measurements from locations that won't be accessible once the spacecraft enters orbit.

Imaging and Data Collection

During this flyby, BepiColombo utilized three monitoring cameras to capture various angles of Mercury's surface as it transitioned from the planet's 'nightside' to the sunlit side. The M-CAM 2 camera showcased particularly striking views revealing more details as the spacecraft entered sunlight, while M-CAM 3 provided additional imagery of a recently named crater.

Notable Craters Observed

Vivaldi Crater

Just four minutes after the closest approach, the spacecraft revealed a large peak ring basin named Vivaldi, named after the composer Antonio Vivaldi. Spanning 210 km across, this crater exhibited remarkable shadows and a gap in its ring, suggesting that lava flows had once inundated the crater floor.

Stoddart Crater

Shortly thereafter, another noteworthy peak ring basin came into view, which was recently named Stoddart in honor of New Zealand artist Margaret Olrog Stoddart. Measuring 155 km across, this crater is expected to be of considerable interest for future investigations. Professor David Rothery from The Open University remarked, "When we were planning for this flyby, we saw that this crater would be visible and decided it would be worth naming due to its potential interest for BepiColombo scientists in the future."

Scientific Significance

BepiColombo's monitoring cameras documented invaluable glimpses of these craters, revealing signs of Mercury's long history of impacts from asteroids and comets. These images lay the groundwork for the scientific work anticipated when BepiColombo officially enters Mercury's orbit in 2026.

Currently, the spacecraft's science instruments are partially operational as it continues its 'stacked' cruise configuration. However, they were active during this flyby, gathering crucial data regarding the magnetic, plasma, and particle environment—data that will be unattainable once in orbit.

Jack Wright, an ESA Research Fellow and M-CAM imaging team coordinator, explained, "BepiColombo is only the third space mission to visit Mercury, making it the least-explored planet in the inner Solar System. The images and science data collected during the flybys offer a tantalizing prelude to BepiColombo's orbital phase, where it will help to solve Mercury's outstanding mysteries."

Future Plans

After this fourth flyby, BepiColombo is slated for two additional gravity assists on December 1, 2024, and January 8, 2025, further adjusting its trajectory towards achieving orbit insertion around Mercury in November 2026.

All M-CAM images captured during this flyby will be accessible to the public in the Planetary Science Archive starting September 13, 2024.