Secondary Crater Populations on the Martian South Polar Layered Deposits

Details Secondary Crater Populations on the Martian South Polar Layered Deposits Secondary Crater Populations on the Martian South Polar Layered Deposits

Dec 2003

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003agufm.p42a0417s&link_type=abstract

American Geophysical Union, Fall Meeting 2003, abstract #P42A-0417

Other

5420 Impact Phenomena (Includes Cratering), 5462 Polar Regions, 6225 Mars

Scientific paper

Understanding the formation and evolution of the Mars South Polar Layered Deposits (SPLD) is an important step toward unraveling Martian climate history. The cratering record on the SPLD suggests that the surface of these deposits has been recently modified. Extremely shallow large (>800 m) impact craters along with a lack of small (<800 m) impact craters might argue for a recent resurfacing event that erased small craters and degraded large ones (Koutnik et al. 2002). Secondary crater fields on the SPLD, produced by the ejection of material from a primary impact event, are important stratigraphic markers that can shed light on the modification history of the deposits. Using MOC, THEMIS and MOLA data, we examined the broad secondary crater field surrounding McMurdo crater (84.5S, 0W) on the SPLD, the field surrounding a 15 km crater at 80.5S, 284W on the SPLD, and the field surrounding a 43 km crater at 81S, 285W off of the SPLD. These datasets provided us with the opportunity to compare and contrast the morphologies of craters in different secondary crater fields both on and off of the deposits. We measured the depth to diameter (d/D) ratios of secondary craters and compared them with those of other primary craters on the deposits measured by Koutnik et al (2002). Among secondary craters on the SPLD, we found a correlation between crater d/D and the steepness of the slope on which the crater resides. Specifically, craters with extremely low d/D ratios (indicating high modification) are found more often on flat areas. Those with high d/D ratios are often associated with scarps and are on higher slopes. This indicates that there have been different resurfacing rates over areas as small as several hundred square kilometers and that modification occurs more readily on flat areas. We examine different mechanisms that may have led to decreased d/D ratios such as blanketing, ice flow, wind erosion or viscous relaxation. We find that the d/D ratios of secondary craters on flat regions of the SPLD are comparable with the extremely low d/D ratios of the primary craters elsewhere on the deposits measured by Koutnik et al (2002). The d/D ratios of secondary craters on the SPLD on slopes are comparable with the d/D ratios of the secondary craters off of the SPLD in rock. This indicates that craters on slopes have been protected from significant modification. Koutnik, M., S. Byrne, and B. Murray (2002) JGR, 107, (E11).

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