Inif it wants to go to Mercury it must brake properly first. The BepiColombo mission of the European Space Agency ESA and the Japanese space agency JAXA must now take this principle to heart. It was launched in 2018 as the third mission to reach the planet closest to the Sun and orbit in 2025. Since its launch, it has slowed down once in the Earth’s gravity, twice in Venus, and once in Mercury itself. She passed Mercury a second time on Thursday – and sent pictures of its surface. The first image released by ESA a few hours after the image was taken at 11:49 German time shows the planet’s surface rich in geological features. The probe looked at the crater landscape from a distance of 920 kilometers. Five minutes earlier it had approached Mercury by 200 kilometers. But BepiColombo was still over Mercury’s night side. The still very oblique incidence of sunlight allows the geological features to be clearly distinguished.
The images are taken from one of the three cameras on the Mercury Transfer Module (MTM) that carries two mission satellites to Mercury, the Mercury Planetary Orbiter (MPO) and the Magnetopheric Orbiter. Both are to orbit the planet in different high polar orbits. The cameras of the transfer module are positioned so that they have a visible solar panel and MPO. The image from camera 2 also shows parts of the support rod for the magnetometer and MPO antenna. The resolution of these cameras is still moderate at 1024 x 1024 pixels. The mission’s high-resolution science cameras will remain safely tucked away during the journey and will not function until Mercury orbit.
The photo shows large impact craters. The multi-ring crater visible behind the magnetometer rod is about 200 kilometers in diameter. To the right of the spar is a cliff that is also about 200 kilometers long and about two kilometers high. This month, it was named the “Challenger Rupes” after a 19th-century expedition vessel. Some of the craters shown are still quite young. A small crater emitting bright rays is visible in the upper right corner of the photo. This is material that was ejected on impact. These structures and glitches, which can also be seen, can provide clues to the inner structure and, in particular, Mercury’s tectonics – a topic that is also high on the 2026 main mission’s science agenda.
Finally, Mercury still has some secrets because when seen from Earth, it is always quite close to the Sun in the sky, making it the most difficult to observe all planets with ground-based astronomy. The Mariner 10 spacecraft passed it three times between 1974 and 1975, and the Messenger spacecraft also flew by between 2011 and 2015. In particular, the latter mission raised a number of questions. For example, it turned out that the chemical composition of the surface was far from what was expected. There are also geological features that are not known from other planets, such as the so-called “Depressions” – Depressions that are likely due to outgassing at the surface and can be found in one of the craters in the upper right corner of the current image. The surface also exhibits tectonic and volcanic activity. Mercury appears to have had a very active geologically past. A better understanding of all of this was the motivation to send BepiColombo on its way. The probe now has four more passes ahead of it. The next one will be held next year.