Mercury's sunlit north viewed by M-CAM 1

This is one of a series of images taken by the ESA/JAXA BepiColombo mission on 8 January 2025 as the spacecraft sped by for its sixth and final gravity assist manoeuvre at the planet. After flying over the planet's north pole, the spacecraft had clear views of Mercury's sunlit northern hemisphere.

Monitoring camera 1 (M-CAM 1) took this photo at 07:12 CET, when the spacecraft was about 1427 km from the planet’s surface. The spacecraft’s closest approach of 295 km took place on the planet's night side at 06:59 CET.

The image shows that large regions of Mercury's heavily cratered surface are smoothed over by lava from volcanic eruptions.

This smoothing over is visible inside the 290 km-wide crater at the right of the image, called Mendelssohn. While its outer rim is still visible, it has been largely filled by the same smooth material that makes up the surrounding plains. Smaller, more recent impact craters dot the otherwise smooth crater.

The vast plains surrounding Mendelssohn, called Borealis Planitia, were formed by the widespread eruption of runny lava some 3.7 billion years ago. The volume of lava making up Borealis Planitia is similar in scale to mass extinction-level volcanic events recorded in Earth’s history, notably the mass extinction event at the end of the Permian period 252 million years ago. Borealis Planitia is bordered by older and hence more heavily cratered terrain.

An old M-CAM favourite, the 1500 km-diameter Caloris basin, appears in the lower left portion of the globe. This is Mercury's largest well-preserved impact structure, and one of the largest in the Solar System. The impact that created it left scars on Mercury's surface up to thousands of kilometres away.

Deep troughs point outwards from the basin's edge, possibly formed by high-speed debris from the Caloris impact scouring the surface. Some of them host relatively bright lava, which looks similar to both the lava on the floor of the Caloris basin and the lava of Borealis Planitia further to the north.

But which way did the lava flow: into the basin, or outwards? We don’t yet know, and this is one of Mercury’s many mysteries that BepiColombo hopes to solve. The foreground of the image shows BepiColombo's solar array (centre right), and a part of the Mercury Transfer Module (lower left).

Click here for the annotated version of this image

[Technical details: This image of Mercury's surface was taken by M-CAM 1 onboard the Mercury Transfer Module (part of the BepiColombo spacecraft), using an exposure time of 4 milliseconss. Taken from a distance of around 1427 km, the surface resolution in this photograph is around 1500 m/pixel. The image has been lightly processed to largely remove instrumental effects due to camera readout without a shutter. The image's brightness and contrast have also been adjusted.]

[Image description: Planet Mercury in the background with its grey, cratered, pockmarked surface. In the foreground are some spacecraft parts.]