BepiColombo snaps Mercury’s dark craters and volcanic plains

These pictures of Mercury’s pockmarked surface are the last we’ll see before the BepiColombo mission begins orbiting the solar system’s innermost world in late 2026.

Since launching in 2018, the joint European-Japanese BepiColombo spacecraft has flown by Mercury six times, using each successive approach to reduce its speed and adjust its flight path to make it easier to get into orbit. While the mission’s main scientific instruments haven’t yet been put to use, the spacecraft’s monitoring cameras have given us some of the clearest views we’ve ever had of the Swift Planet.

The European Space Agency (ESA) has now released three of the most captivating images from BepiColombo’s most recent flyby on 8 January, taken from around 300 kilometres above Mercury’s surface as it flew over the planet’s north pole and northern regions.

“It meant getting up at 5.30am, but once close-up images started to appear in our shared folder, it was worth it,” says David Rothery at the Open University, UK. “We had studied some simulated views in advance and used these to devise our imaging strategy, but what we saw was better than expected.”

The image above, taken over the planet’s north pole, shows the clear division between sunlight and darkness on Mercury, which researchers call the terminator line. Mercury has some of the hottest temperatures in the solar system where sunlight falls on its scorched surface, but it also has some of the coldest, in craters that are permanently shadowed by their rims.

Some of these shadowed crater regions can be seen lying along the terminator line in the image. “It was great looking down on Mercury’s north pole, and even seeing the sunlit tip of the central peak inside the crater Tolkien, whose floor is in permanent shadow,” says Rothery.

Scientists have found some evidence that these cratered regions contain frozen water. One of BepiColombo’s main mission objectives is to discover whether that water really exists, and how much there is.

Mercury also contains an expansive volcanic plain known as Borealis Planitia, which BepiColombo spied on its flyby. Researchers think these plains were formed from vast lava flows more than 3 billion years ago that flooded existing craters, some of which can be seen in the above image. Most of these flooded plains are smooth, with a few impact craters that must have been formed more recently.

The Caloris Basin, which at 1500 kilometres wide is Mercury’s largest crater, appears as a semi-circular patch of lighter-coloured ground extending from the horizon towards the bottom left of the image. Scientists hope to learn more about how this crater, the Borealis Planitia and the solidified lava flows between are connected once BepiColombo starts orbiting the planet.

The bright region near the top of the planet in this image is called Nathair Facula, and researchers think it is the remnant of Mercury’s largest ever volcanic eruption. The centre of the region is a 40-kilometre-wide volcanic vent, which appears to have been the source of at least three huge eruptions that spewed volcanic material for hundreds of kilometres.

“[Nathair Facula] was right on the verge of what we expected to be able to make out, but having published on it based on images from the previous NASA mission to Mercury, it was exciting to glimpse it again,” says Rothery. “It is a very important science target for several of BepiColombo’s instruments when we get into orbit, because it offers our best chance to work out what it is about Mercury’s composition that has allowed explosive volcanic eruptions to continue through much of the planet’s history.”