ENDOGENIC FEATURES IN THE SOUTH POLAR REGION OF MARS AND POSSIBLE TERRESTRIAL ANALOGUES
KOUTNIK, MICHELLE R. University of Calgary.
Murray, Bruce . California Institute of Technology.
Byrne, Shane . California Institute of Technology.
The narrow angle (NA) Mars Orbiter Camera (MOC) aboard the Mars Global Surveyor (MGS) mission has provided detailed imagery of the South Polar Layered Deposits (SPLD) and the south polar residual cap revealing features previously unable to be identified. There are a multitude of features we have found and believe that they have a possible endogenic origin as opposed to being impact craters. The observed endogenic features often have particular associations and negative, circular, but non crater-like forms. The presented features in different areas of the south polar region have different morphological characteristics.
The region of the SPLD from at least 190 - 230 W, 85 - 87 S, just west of Chasma Australe, is the primary location for a different clustering of negative, circular pits. This area is topographically unique because of the extensive grooves of an undetermined origin cut into it. We have informally termed this grooved area the ?wire brush? region and it is shown in Figure 1. We have not recognized such a pattern elsewhere on Mars and only in one other small area in the SPLD. It is suggestive of erosion by an external agent that maintained a coherent pattern over several hundred kilometers scale, such as wind or glaciation. The pits in this region are all approximately 10 ? 100 m in diameter and have been ruled out as small primary impact craters or secondary craters based on the lack of crater-like associations and the high number of features observed over this entire area. A significant association that has been noted in some images is that the pits can be grouped in circular patches of slightly lower topography over a particular region, as shown in Figure 2. Other pit-like features are noted in different areas on the SPLD, particularly from at least 120 - 190 W, 85 - 87 S. An example of these features, shown in Figure 3, exhibit more irregularities in shape and are also frequent over this region.
There are terrestrial features that have the same size range and are similar in appearance and distribution to the south polar pits. These glacial potholes are thought to occur in association with glacial surging on Earth but a detailed process of formation is not well constrained [Post and LaChapelle, 1971; Sturm, 1987]. The analogue to the observed Martian features is only by appearance and size distribution thus far. The possibility for a similar mechanism of formation has not yet been determined and as well other terrestrial analogues are also considered. Another possibility is that these features may be associated with the termed Martian ?swiss cheese? terrain found on the residual cap [Ingersoll et al., 2000; Thomas et al., 2000].
The origin of these endogenic features has not been determined and it is possible that different mechanisms are responsible for the features on the residual cap and on different regions of the SPLD. These features are most unlikely impact craters or secondary populations and may indicate characteristics of south polar processes and will likely provide insight into the past south polar environment.
Ingersoll, A.P., et al., 2000, Spring and Summer Changes at the south pole as seen by the Mars Orbiter Camera, Mars Polar Science II (2000), #4076.
Post, Austin and LaChapelle, Edward. Glaicer Ice. University of Washington Press, 2000, pg. 78-79.
Sturm, M., 1987, Observations on the Distribution and Characteristics of Potholes on Surging Glaciers, Journal Geophys. Res. 92, 9015-9022.
Thomas, P.C., et al., 2000, North-South geological differences between the residual polar caps on Mars, Nature 404, 161-163.
Figure 1. "Wire brush" region of the SPLD, at least 190 - 230 W, 85 - 87 S. This is also the primary location of circular, negative pits we highlight here. The origin of these extensive grooves is unknown but suggestive of glaciation.
Figure 2. Portion of MOC NA frame m110-2900, at 87 S, 203 W. This image shows the circular, negative pits grouped within larger circular, negative depressions.
Image processing in progress...
Figure 3. MOC NA frame m110-0014, at 87 S, 148 W. This image shows a morphologically different distribution of circular, negative pits in the region 120 -190, 85 -87 S. As apparent in this image, these pits are often linearly linked together.
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