Extraterrestrial Impact Craters

One of the first topics we covered in astrogeology is impact craters. They are characterized by circular or ellipitical depressions in a planetary body and sometimes contain central peaks. The shape is a function of the angle at which the impactor hits the body and the central peak is a product of isostatic rebound. The more shallow the angle at which the impactor hits, the more oblique the crater. The central peak forms as the crust in the center “springs” to a higher elevation after the impact. The debris that gets kicked up during this process surrounds the crater and becomes the ejecta blanket.

What’s interesting is that impact craters follow nearly the same pattern throughout the solar system. From Venus to the Moon, and Mercury, they all look fairly similar.

Tycho Crater on the Moon. Notice the central peak in the crater? (Image taken by NASA Lunar Orbiter. Courtesy University of Hawaii)

Radar image of the impact crater at Guinevere Planitia on Venus. Here the central peak is fairly apparent, but more noticeable is the surrounding ejecta blanket. (Image from JPL)

 

Donne crater from Mercury. (Image from NASA)

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