Here on we’re used to seeing volcanoes as towering mountains with steam-belching peaks or enormous fissures oozing lava. But on Mercury volcanic features often take the form of deep, sunken pits surrounded by bright reflective material. They look like craters but are more irregularly-shaped, and here we have a view from MESSENGER of a cluster of them amidst a rugged landscape that stretches all the way to the planet’s limb.
The image shows a group of pyroclastic vents on Mercury, located just north and east of the 180-mile (290-km) -wide, double-ringed Rachmaninoff crater. The vents lie in the center of a spread of high-reflectance material, sprayed out by ancient eruptions.
An older vent can be seen at the bottom right, looking like a crater but with non-circular walls.