Planet Mercury: BepiColombo Spacecraft's Close-up Flyby Images | ESA/JAXA
On January 8, 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 kilometers 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.
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, here are the best three images from BepiColombo's sixth close encounter with the planet, and what they reveal about Mercury.
After flying through Mercury's shadow, BepiColombo's monitoring camera 1 (M-CAM 1) captured the first close views of Mercury's surface. Flying over the ‘terminator’—the boundary between day and night—the spacecraft had a unique opportunity to peer directly down into the forever-shadowed craters at planet's north pole.
Image 1: Mercury's shadowy 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.
Image 2: Mercury's sunlit north viewed by M-CAM 1
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 1,500 km. The impact that created this basin scarred Mercury's surface up to thousands of kilometers 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 color 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 how this lava moved: into the Caloris basin, or out of it?
Image 3: Lava and debris brighten Mercury's surface
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.
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 do not 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 center 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.
Image Date: Jan. 8, 2025
Release Date: Jan 9, 2025
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