11 November 2004
This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image captures
some of the complexity of the martian upper crust. Mars does not simply
have an impact-cratered surface, it's upper crust is a cratered volume.
Over time, older craters on Mars have been eroded, filled, buried, and in
some cases exhumed and re-exposed at the martian surface. The crust of
Mars is layered to depths of 10 or more kilometers, and mixed in with the
layered bedrock are a variety of ancient craters with diameters ranging
from a few tens of meters (a few tens of yards) to several hundred
kilometers (more than one or two hundred miles).
The picture shown here captures some of the essence of the layered,
cratered volume of the upper crust of Mars in a very simple form. The
image shows three distinct circular features. The smallest, in the lower
right quarter of the image, is a meteor crater surrounded by a mound of
material. This small crater formed within a layer of bedrock that once
covered the entire scene, but today is found only in this small remnant
adjacent to the crater. The intermediate-sized crater, west (left) of the
small one, formed either in the next layer down--that is, below the layer
in which the small crater formed--or it formed in some layers that are
now removed, but was big enough to penetrate deeply into the rock that is
near the surface today. The largest circular feature in the image, in the
upper right quarter of the image, is still largely buried. It formed in
layers of rock that are below the present surface. Erosion has brought
traces of its rim back to the surface of Mars. This picture is located
near 50.0°S, 77.8°W, and covers an area approximately 3 km (1.9 mi)
across. Sunlight illuminates this October 2004 image from the upper
left.