Lunar and Planetary Science XXIX 1173.pdf GROUND-ICE DISTRIBUTION ON MARS BASED ON GIS ANALYSIS. F. Costard1 and J.P.Gosset². 1Laboratoire de Géologie Dynamique de la Terre et des Planètes, 91405 Orsay Cédex, France. ² Centre de Ressources Informatiques, Université de Caen, 14032 Caen, France. [email protected] Introduction. In order to quantify the spatial in large topographic basins near and below –1000 distribution of martian ground-ice, a global study m, especially in areas that are close to the con- of rampart craters was undertaken to determine vergent terminations of outflow channels (8). their temporal and spatial relations with the sur- - At about 41°S, 257°W to the east of Hellas rounding morphostructural units. Rampart craters Planitia, a regional concentration of rampart cra- all over planet Mars have been systematically ters suggests the presence of a volatile-rich measured and mapped using a GIS database of sedimentary plain at the mouth of Harmaklis, geologic and topographic informations (1). Ma’adim and Reull Valles. The occurrence in the Methodology. Rampart crater ejecta mor- same area of three channels, at a latitude higher phologies are the result from impact into subsur- than 40° and within a topographic basin are opti- face volatile reservoirs with different physical or mal conditions for the development of a perma- structural properties (2,3,4,5,6). In order to pro- nent ground-ice (2). duce statistically significant results, all rampart - This GIS analysis reveals a linear concentra- craters that are visible in 1:2000000-scale Viking tion of rampart craters along Kasei Valles. photomosaics have been digitized. Data were - Young volcanic units in Tharsis Montes ex- collected for 2561 rampart craters in the size hibit a low density of rampart craters, excepted for range 1-40 km (2). provinces surrounding Tharsis and Elysium re- We have examined the global and regional gions. Particularly SE Arcadia Planitia and East of distribution of rampart craters with a simple sub- Elysium exhibit an unusual concentrations of division into three types. Type 1 exhibits a single rampart craters. The explanations proposed is the continuous and multilobate ejecta with peripheral volatile enrichment beneath the Tharsis and Ely- ridges. Type 2 ejecta includes a double continu- sium lavas (5). ous ejecta deposit. This analysis includes among Conclusion. This GIS study confirms some rampart craters the so-called “pedestal” (type 3) previous studies, but also gives some new obser- which are believed to be the erosional remnants vations about the regional concentrations of ram- of ejecta blankets. part craters and new interpretations about the Our analysis includes the farthest lateral ex- interactions between the elevation, the latitude tent attained by type 1 and 2 fluidized ejecta. An and the geological units. increase of water content should increase the mobility of the ejecta. Ejecta mobility can be ex- References: (1) Smith, D.E. and T. Zuber pressed by the ratio, of the maximum diameter of (1996). Science, vol. 271, 184-188. (2) Costard, ejecta deposits divided by the diameter of the F. (1989). Earth, Moon and Planets. 45: 265-290. parent crater (2,3,6). (3) Mouginis-Mark, P.J. (1979) J. Geophys. Res. Interpretations. 84, 8011-8022. (4) Barlow, N.G. and Bradley, T.L. - This GIS analysis reveals that type 1 ejecta, Icarus, 87, 156-179. (5) Cave, J. A. (1993). J. together with low mobility ejecta, are frequently Geophys. Res.98, 11079-11097. (6) Kuzmin, R. observed in the equatorial region. The GIS re- et al. (1988). 19th LPSC abstract volume. (7) veals a good relationship between type 1 ejecta Thomas, P. and Masson Ph., (1985) Earth, Moon and ridged plains for Coprates, Lunae Planum, and Planets, 34, 169-176. (8) Costard, F. and J. Western Amazonis, Chryse Planitia, South Ely- Kargel (1995). Icarus. 114, 93-112.. sium and Syrtis Major. These results are in agreement with previous works (7). Acknowledgements: This work is supported by - Type 2 ejecta with high mobility, occur at a Programme National de Planétologie de l'Institut Na- latitude higher than 40°N (where ground-ice re- tional des Sciences de l'Univers (CNRS, France). mains stable) in Utopia and Acidalia Planitiae. The highest percentage of rampart craters occur Lunar andPlanetaryScienceXXIX GROUND-ICE DISTRIBUTIONONMARSBASEDGISANALYSIS.F.CostardandJ.P.Gosset. Figure 1 : GIS database of martian ground-ice based on rampart crater distribution and ejecta mobility. Circles are proportional to the ejecta mobility (see text). Sinu- soidal projection. Data from : F. Costard (rampart craters), M.T. Zuber 1996 (topography), USGS geological units, modified). GIS cartography: J.P. Gosset Caption : 1:young sedimentary plain (upper Hesperian age) , 2: young volcanic unit (Amazonian age), 3: old volcanic unit (Hesperian age), 4: ridged plain mate- rials (Hesperian age), 5: old sedimentary plain (lower Hesperian age), 6: cratered upland (Noachian age), 7: zone of transition between highland and lowland prov- inces, 8: chaotic terrains, 9: Impact basin, 10: ejecta, 11: volcanic edifice, 12: eolian deposits, 13: polar layered deposits, 14: polar deposits, 15: type 1 ejecta, 16: type 2 ejecta, 17: type 3 ejecta. 1173.pdf.