Featured Image - 12/2/2008
Crater Chain in Mendeleev

Catena Mendeleev is a linear crater chain probably formed by the impact of fragments (called 'secondaries' by planetary scientists) that were ejected by the impact that formed Tsiolkovsky Crater, which is 850 kilometers to the southwest of Mendeleev. Crater chains formed from secondary impacts are radial to their parent crater. Secondary craters in a chain are usually elongate in shape, with irregular rims and a 'splashed' appearance of the ejecta. Sometimes secondaries form 'herringbone ridges,' which are often difficult to see in images taken at high sun angles. Secondary crater chains tend to occur in a zone immediately surrounding a large primary crater, like the chain in Figure 2. However, larger impacts can move significant amounts of ejecta, including crater chains, far from the primary crater.

Other crater chains are thought to be volcanic in origin. With the volcanic variety, the craters are lined up along a common fault or set of faults, and each crater produces a blanket of volcanic ejecta. Volcanic crater chains are not assocated with a parent crater. Occasionally it is difficult to differentiate between the two types of crater chains. Only further imagery of the lunar surface, like the high-resolution images that will be collected by the Lunar Reconnaissance Orbiter Camera will help us correctly distinguish volcanic and impact crater chain features.

 
Figure 1. The smooth floor of Mendeleev includes many craters and is approximately 4.2 to 4.3 billion years old, as shown by crater counts. Mendeleev is ~313 kilometers in diameter. Catena Mendeleev is the linear crater chain stretching NE to SW across crater Mendeleev. Terracing of the crater wall is visible in the upper left hand corner. Sun elevation is 41.0 degrees. (Apollo Image AS16-M-0063 [NASA/JSC/Arizona State University])

 
Figure 2. The crater Euler, which is about 40 kilometers in diameter, has an ejecta blanket which contains textbook examples of impact crater chains. The inset shows a magnified view of the irregular shape and V-shaped ridges. Sun elevation is 0.0 degrees. (Apollo Image AS15-M-1159 [NASA/JSC/Arizona State University])

Sources: Apollo Over the Moon: A View From Orbit (1978) H. Masursky, G.W. Colton, F. El-Baz, eds. NASA Sp-362. http://www.hq.nasa.gov/office/pao/History/SP-362/contents.htm
Laboratory Simulation of the Herringbone Pattern Associated with Lunar Secondary Crater Chains (1974) V.R. Oberbeck and H.R. Morrison. The Moon. D. Reidel Publishing Company, Dordrecht-Holland.

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