09/01/2025
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On 8 January 2025, the ESA/JAXA BepiColombo mission flew past Mercury for the sixth time, successfully completing the final ‘gravity assist manoeuvre’ needed to steer it into orbit around the planet in late 2026. The spacecraft flew just a few hundred kilometres above the planet’s north pole. Close-up images expose possibly icy craters whose floors are in permanent shadow, and the vast sunlit northern plains.
At 06:59 CET, BepiColombo flew just 295 km above Mercury’s surface on the planet’s cold, dark night side. Around seven minutes later, it passed directly over the Mercury’s north pole before getting clear views of the planet’s sunlit north.
European Space Agency (ESA) Director General Josef Aschbacher revealed the first image during his Annual Press Briefing on 9 January. As during BepiColombo’s previous flybys, the spacecraft’s monitoring cameras (M-CAMs) did not disappoint.
This flyby also marks the last time that the mission’s M-CAMs get up-close views of Mercury, as the spacecraft module they are attached to will separate from the mission’s two orbiters – ESA’s Mercury Planetary Orbiter and JAXA’s Mercury Magnetospheric Orbiter – before they enter orbit around Mercury in late 2026.
Celebrating the M-CAMs’ final hurrah, let’s explore the best three images from BepiColombo’s sixth close encounter with the little planet, and what they reveal about mysterious Mercury.
Peering into Mercury’s darkest craters
After flying through Mercury’s shadow, BepiColombo’s monitoring camera 1 (M-CAM 1) got the first close views of Mercury’s surface. Flying over the ‘terminator’ – the boundary between day and night – the spacecraft got a unique opportunity to peer directly down into the forever-shadowed craters at planet’s north pole.
The rims of craters Prokofiev, Kandinsky, Tolkien and Gordimer cast permanent shadows on their floors. This makes these unlit craters some of the coldest places in the Solar System, despite Mercury being the closest planet to the Sun!
Excitingly, there is existing evidence that these dark craters contain frozen water. Whether there is really water on Mercury is one of the key Mercury mysteries that BepiColombo will investigate once it is in orbit around the planet.
A surface shaped by impacts and lava
To the left of Mercury’s north pole in M-CAM 1’s view lie the vast volcanic plains known as Borealis Planitia. These are Mercury’s largest expanse of ‘smooth plains’ and were formed by the widespread eruption of runny lava 3.7 billion years ago.
This lava flooded existing craters, such as the Henri and Lismer craters highlighted in the image. The wrinkles in the surface were formed over billions of years following the solidification of the lava, probably in response to the planet contracting as its interior cooled down.
Another M-CAM 1 image, taken just five minutes after the first, shows that these plains extend over a large part of Mercury’s surface. Prominently visible is the Mendelssohn crater, whose outer rim is barely visible above its flooded interior. Just a handful of smaller, more recent impact craters dent the smooth surface.
Further out, but still within the Borealis Planitia, the Rustaveli crater suffered a similar fate.
On the bottom left of the image lies the massive Caloris basin, Mercury’s largest impact crater, which spans more than 1500 km. The impact that created this basin scarred Mercury’s surface up to thousands of kilometres away, as evidenced by the linear troughs radiating out from it.
Above a particularly large trough, a boomerang-shaped curve brightens the surface. This bright lava flow appears to connect to a deep trough below it. It appears similar in colour to both the lava on the floor of the Caloris basin and the lava of Borealis Planitia further north. Yet another mystery that BepiColombo hopes to solve is which way this lava moved: into the Caloris basin, or out of it?
On Mercury, a bright surface is a young surface
While M-CAM’s images might not always make it appear so, Mercury is a remarkably dark planet. At a first glance the cratered planet may resemble the Moon, but its cratered surface only reflects about two-thirds as much light.
On this dark planet, younger features on the surface tend to appear brighter. Scientists don’t yet know what exactly Mercury is made of, but it is clear that material brought up from beneath the outer surface gradually becomes darker with age.
BepiColombo’s third image selected from this flyby, taken by M-CAM 2, shows spectacular examples of the two things that bring bright material to the surface: volcanic activity and large impacts.
The bright patch near the planet’s upper edge in this image is the Nathair Facula, the aftermath of the largest volcanic explosion on Mercury. At its centre is a volcanic vent of around 40 km across that has been the site of at least three major eruptions. The explosive volcanic deposit is at least 300 km in diameter.
And to the left lies the relatively young Fonteyn crater, which formed a ‘mere’ 300 million years ago. Its youth is apparent from the brightness of the impact debris that radiates out from it.
Throughout its mission, several BepiColombo instruments will measure the composition of both old and new parts of the planet’s surface. This will teach us about what Mercury is made of, and how the planet formed.
Finishing in style
“This is the first time that we performed two flyby campaigns back-to-back. This flyby happens a bit more than a month after the previous one,” says Frank Budnik, BepiColombo Flight Dynamics Manager. “Based on our preliminary assessment, everything proceeded smoothly and flawlessly.”
“BepiColombo’s main mission phase may only start two years from now, but all six of its flybys of Mercury have given us invaluable new information about the little-explored planet. In the next few weeks, the BepiColombo team will work hard to unravel as many of Mercury’s mysteries with the data from this flyby as we can,” concludes Geraint Jones, BepiColombo’s Project Scientist at ESA.
About BepiColombo
Launched on 20 October 2018, BepiColombo is a joint mission between the European Space Agency (ESA) and the Japan Aerospace Exploration Agency (JAXA), executed under ESA leadership. It is Europe’s first mission to Mercury.
The mission comprises two scientific orbiters: ESA’s Mercury Planetary Orbiter (MPO) and JAXA’s Mercury Magnetospheric Orbiter (Mio). The European Mercury Transfer Module (MTM) carries the orbiters to Mercury.
After arrival at Mercury in late 2026, the spacecraft will separate and the two orbiters will manoeuvre to their dedicated polar orbits around the planet. Starting science operations in early 2027, both orbiters will gather data during a one-year nominal mission, with a possible one-year extension.
All M-CAM images will be made publicly available in the Planetary Science Archive.
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