Mars Exploration Rover Field Observations of Impact Craters at Gusev Crater and Meridiani Planum
Abstract
The Mars Exploration Rovers have provided a field geologist's perspective of a number of impact craters in various states of degradation along their traverses at Gusev crater and Meridiani Planum. Spirit has traversed a generally low relief somewhat rocky plain dominated by shallow circular depressions called hollows. Hollows are typically 1-20 m in diameter, generally have rocky rims characterized by angular and fractured blocks, and smooth soil filled centers. Hollow morphology and size-frequency distribution strongly argue that they are impact craters filled in by eolian material. Three larger craters 100-200 m in diameter imaged by Spirit also have been filled in with soil (depths of only 3-6 m). Bonneville appears to be a relatively fresh 200 m diameter crater impacted into unconsolidated blocky debris (no outcrop). Rock abundance and the largest block size increases by a factor of 2-4 from the discontinuous ejecta, through the continuous ejecta to the rim, suggesting a relatively pristine ejecta blanket. The crater rim is ∼5 m high, the crater floor only 10 m deep, and the rubble walls are shallowly dipping ( ∼11° ). The walls show no signs of mass wasting and eolian material deposited inside is variable, but limited at the bottom to ∼1-2 m thickness by protruding boulders. The low depth to diameter ratio of Bonneville and other small fresh craters in and on its walls suggest that they formed as secondary craters, a conclusion also suggested by very low depth/diameter ratios measured from fresh craters in stereo high-resolution orbital images. Far fewer craters have been imaged by Opportunity at Meridiani Planum due to its relatively young surface age and all have been modified by eolian activity with sediment in their interiors and modified rims. Three well-characterized impact craters are Endurance, Eagle, and Fram, which are 150 m, 20 m and 10 m in diameter, respectively. Fram appears freshest with ejecta blocks on the surface, Endurance retains steep interior walls, and Eagle appears the most degraded with a highly modified shallow sand and granule filled interior. All expose sedimentary rocks in their walls. Many other shallow sandy circular depressions (1-10 m in diameter) have been imaged by Opportunity, but most lack raised rims and thus are difficult to distinguish from modified collapse pits along northeast-trending fractures.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2004
- Bibcode:
- 2004AGUFM.P33B..01G
- Keywords:
-
- 5420 Impact phenomena (includes cratering);
- 5470 Surface materials and properties;
- 6225 Mars