Tuesday, November 24, 2009

Craters on the dark side of the moon

When people envision a "moonscape" it probably looks something like this -- craters, craters everywhere.

There are two types of impact craters on the Moon: primary and secondary. Primary craters form as the result of an asteroid or comet (or spacecraft) impacting the Moon. Secondary impact craters formed from the impact of ejecta expelled during primary crater formation. Secondary impact craters dominate this scene, possibly from the relatively recent impact that created nearby Jackson crater (43.5 miles across), located 42 miles to the west.

Clusters of secondary craters help geologists determine the relative ages of features on the moon. Image width is nearly seven football fields across. Credit:NASA/Goddard Space Flight Center/Arizona State University.

Geologists use small secondary craters to help unravel the stratigraphy of the lunar surface. These secondary craters reside on the floor of a 8.7 mile wilde crater. What is the age of this host crater? If these secondary craters originated from the Jackson event, then it is a fair bet the Jackson impact was more recent. If you look at the bottom of this NAC frame in the LROC Image Gallery at ASU, you can see that this crater also has a very subdued rim, in contrast to Jackson's well-defined rim, providing more evidence of it's age.

Related Link:

› LROC site at Arizona State University

Arizona State University

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