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.