Physics
Scientific paper
Dec 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002agufm.p62a0365u&link_type=abstract
American Geophysical Union, Fall Meeting 2002, abstract #P62A-0365
Physics
5420 Impact Phenomena (Includes Cratering)
Scientific paper
We have used the 1/64th degree digital elevation model of Mars obtained from the Mars Orbiter Laser Altimeter (MOLA) to measure the dimensions of impact craters on the Northern Plains of Mars. Our objective is to search for spatial variations in crater geometry (e.g., the depth/diameter ratio or ejecta volume/crater volume ratio) that might indicate variations in target properties or the resurfacing history of Mars with time. Our initial analysis is focused on the Northern Plains because of the apparent uniform surface material and relatively constant elevation (about -3.8 to -5.2 km relative to the MOLA datum). We have studied craters in three different areas: Utopia Planitia (90 craters between 0.8 km to 39.8 km dia., over the latitude range 12N to 60N), Acidalia Planitia (49 craters 7.4 to 58.9 km dia., 33N to 61N) and Amazonis Planitia (61 craters 0.9 to 26.8 km dia., 23N to 61N). We measured the following parameters from the MOLA data using an in-house software package written in IDL by Harold Garbeil (Univ. Hawaii): (a) crater latitude and longitude; (b) crater diameter; (c) crater maximum and average depth; (d) crater cavity volume; (e) crater rim crest height and volume; and (f) average thickness and total volume of the inner ejecta layer. These parameters are measured relative to a user-defined surface that lies around the perimeter of the crater beyond the range of the ejecta layers. These data reveal some fascinating aspects of Martian cratering that were only hinted at from analysis of Viking Orbiter images. We find evidence for: (1) a progressive decrease towards higher latitudes in the depth/diameter ratio for craters of a comparable size; (2) the volume of the inner ejecta layers often exceeds the crater cavity volume, particularly in the case of craters equatorward of 34N; (3) two trends exist in the crater diameter/volume ratio, with the transition occurring at the diameter range 6 to 18 km; (4) there is little correlation between average rim height and crater diameter; (5) ejecta volume and crater rim volume are weakly correlated, but examples can be found where this ratio varies by more than 3 orders of magnitude; (6) little difference between the three geographic regions appears to exist. We also note that we have found an additional 48 craters where the crater floor is at a higher elevation than either the ejecta deposits or the surrounding plain. The implications of these observations will be discussed.
Mouginis-Mark Peter J.
Ui C. S.
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