Sunrise and shadows
The joint European-Japanese BepiColombo mission captured this view of Mercury on 23 June 2022 as the spacecraft flew past the planet for its second of six gravity assist manoeuvres at Mercury. This image was taken at 09:48:22 UTC by the Mercury Transfer Module’s Monitoring Camera 1 (MCAM-1) when the spacecraft was 680 km from Mercury, the first image capturing the illuminated surface of Mercury during the flyby. Closest approach of 200 km took place shortly before, at 09:44 UTC.
The cameras provide black-and-white snapshots in 1024 x 1024 pixel resolution. This image has been 'block replicated' to 2048 x 2048 pixels. Some imaging artefacts such as horizontal striping are also visible. The cameras positioned such that various parts of the spacecraft can be seen. MCAM-1 looks along one of the solar arrays of the Mercury Transfer Module (left in this orientation), together with part of the spacecraft body (top right) where its thermal blanket can be seen. In this image, north is up.
Only a small portion of Mercury is visible in this frame but the surface features and particularly the roughness of the terrain are enhanced by the shadows cast by the Sun, which, shortly after local dawn, was low in the sky. To the left of the image, only the rims of craters are visible along the terminator (the location between night and day), while their floors are covered in shadow (for example, Benoit crater).
Thanks to these lighting conditions, some deep trough-like features propagating radially from the centre of the Eminescu crater are clearly visible. These are very closely spaced chains of so-called secondary craters formed by the impact of material ejected from the central primary crater. These features are one observation that can allow us to determine the relative age of a crater since they tend to degrade and disappear over time. The brightness of a surface provides another clue, as fresh, bright features tend to fade over time as well. Eminescu’s floor is not just bright because of its young age, however, but also because of the clustering of hollows around its central peak. Hollows are a unique geologic feature to Mercury, and will be studied in depth once BepiColombo is in orbit around the planet.
Another bright area to the right looks overexposed in the image because of the bright rays emanating from the Xiao Zhao crater that cover that region. Although the rim of this rayed crater is not visible, it is probably located within the overexposed area.
Click here for an annotated version of this image.
The gravity assist manoeuvre was the second at Mercury and the fifth of nine flybys overall. During its seven-year cruise to the smallest and innermost planet of the Solar System, BepiColombo makes one flyby at Earth, two at Venus and six at Mercury to help steer on course for Mercury orbit in 2025. The Mercury Transfer Module carries two science orbiters: ESA’s Mercury Planetary Orbiter and JAXA’s Mercury Magnetospheric Orbiter. They will operate from complementary orbits to study all aspects of mysterious Mercury from its core to surface processes, magnetic field and exosphere, to better understand the origin and evolution of a planet close to its parent star.
