This image of Mercury's surface was acquired during MESSENGER's first
flyby of the planet on January 14, 2008, through the lens of the Narrow
Angle Camera (NAC), part of the Mercury Dual Imaging System (MDIS). The
image was acquired when MDIS was 11,588 km (7,200 miles) from Mercury's
surface.
Several processes have acted to sculpt Mercury's surface over time, and
evidence of them is abundant in this image. This scene shows at least five
different events in Mercury's surface history. The large crater to the
lower left of the image measures ~230 km (143 miles) in diameter and has a
prominent crater, about 85 km (53 miles) across, nestled inside it, south
of its center. Both of these craters were subsequently filled with a
material that appears to have been emplaced in a relatively fluid form, as
evidenced by the fact that the material "embays" or onlaps the ejecta
blanket surrounding the rim of the smaller crater. The larger crater is
filled almost to its rim with this smooth plains material, which is
thought to be of volcanic origin. Subsequent to the plains emplacement was
the formation of the linear feature trending southwest to northeast across
the lower half of the scene. This feature is a lobate scarp, similar to
many others found on Mercury's surface, and thought to originate when
compressional stresses crumpled the surface. The last major episode in the
history of this region is the impact that formed the large crater at the
top of the image. The formation of this crater resulted in impact-derived
material, known as ejecta, being thrown out radially for large distances.
Some of this ejecta formed chains of "secondary" craters as it impacted
back onto the surface; some of these secondary craters are visible atop
the lobate scarp.
By careful examination of the relationships among features within images
such as these, Mercury's surface history can be teased out, enabling us to
better understand the evolution of this planet and other terrestrial
worlds.
These images are from MESSENGER, a NASA Discovery mission to conduct the
first orbital study of the innermost planet, Mercury. For information
regarding the use of images, see the MESSENGER image use policy.
