[Previous] | [Session 22P] | [Next]
N. G. Barlow (U. Central FL)
Crater clusters are groups of 4 or more closely-spaced impact craters which show evidence of having formed simultaneously. The most common types of crater clusters are those produced as secondary craters during formation of a primary impact crater. Magellan images of impact craters <15-km-diameter on Venus, however, revealed that crater clusters also can form due to atmospheric break-up of meteoritic material. Hartmann et al (1994; BAAS, 26, 116) proposed that isolated crater clusters on Mars may reflect the break-up of either (1) weak cometary material through the current thin martian atmosphere, or (2) slightly stronger materials through a thicker past atmosphere.
The author has undertaken a study to identify the distribution of isolated crater clusters on Mars and determine if such clusters may suggest past episodes of thicker atmospheric conditions. The identification of crater clusters in the northern hemisphere is now complete. The clusters were identified using Viking Orbiter imagery of 500 m/px resolution or better. The collected data include information on location, number of craters in the cluster, sizes of the craters, and orientation of the cluster. Although most crater clusters found on Mars are secondaries associated with larger impacts, there are a number of isolated crater clusters which may have formed by break-up in the martian atmosphere. In two cases, the crater clusters contain large craters (>5-km-diameter), although most of the crater clusters consist of craters <2-km-diameter. The project is currently being extended to the southern hemisphere of the planet and stratigraphic relationships are being determined to constrain the time period(s) during which these isolated crater clusters formed.