CRATER INFILLING PROCESSES IN THE SINUS SABAEUS REGION OF MARS

Impact cratering is arguably the most important surficial geologic process occurring on the terrestrial planets (with the exception of Earth). Since impact craters can be considered closed systems, they are excellent tools to measure the degree and type of erosional degradation occurring on a planet’s surface. However, the exact timing and contribution of each erosional process occurring on Mars has remained uncertain due to poor characterizations of crater morphology. Recently, the Mars Orbiter Laser Altimeter (MOLA) has returned near global coverage of the surface topography at an approximately 1 km² resolution. These new, high resolution data permit for the first time an accurate study of the morphologic characteristics of Martian craters. Using these data and images of Mars returned from the Viking missions, we have created a comprehensive database of crater characteristics in the Sinus Sabaeus region of Mars (approximately 315-360°W, 0-30°S).

The estimated amount of infilling each crater in the region has undergone was calculated by comparing the actual depth of the crater to the estimated depth of the crater when it was fresh, as modeled by Garvin and Frawley (2001). The comparison of the crater’s present depth and percent infilled results in a bimodal distribution, which is interpreted to represent two distinct populations of craters – those formed during the Noachian which are highly degraded and post-Noachian fresh craters which have experienced very little infilling. This interpretation is supported by other morphologic characterizations, such as floor slope and sharpness of the crater rim.

We have compared the percent infilled values for the craters observed in Sinus Sabaeus to those produced by various simple infilling models in an attempt to distinguish which processes have most greatly affected the region. Initial modeling of some infilling processes shows that for the majority of processes, the crater tends to infill very quickly initially and then the rate of infilling decreases significantly as the crater becomes more shallow.