Background There are several theories that state that Martian sinkholes as the result of large evaporite deposits and erosion are impossible. The past presence of large oceans as well as the detection of gypsum, halite, calcite, and clays in Martian meteorites seems to point toward the types of large scale deposits necessary to create this type of sinkhole. Introduction The focus area of this study is the Circum-Chryse outflow channels in Xanthe and Margaritifer, Terrae and Lunae Planum and their outwash plains in Chryse Planitiae. (Figure 1) Based upon gamma-spectroscopy studies of the surface, the area is believed to have a high subterranean water abundance. (Figure 2) The outflow channel beds of this area also contain a large number of depressions thought to be the result of a downward outflow of material. Another key aspect of this study is the development of a GIS- based atlas of Mars that can incorporate files in the Planetary Data System format. This will allow us to better map the surface features and more easily determine elevations, diameters, etc. Fig. 2. Epithermal neutrons measurements for 55 days of mapping.. The map is normalized to 1 at the highest count rate, 0.26 counts/s in Solis Planum (270°E, 30°S). Study area enclosed in box.. Preliminary Assumptions on Martian Sinkholes They are most likely to be found in regions where large quantities of water once existed The low pH and low gravity environment allows the sinkholes on Mars to grow larger than the sinkholes on Earth making them easier to find The low pH and low gravity environment allows the sinkholes on Mars to grow larger than the sinkholes on Earth making them easier to find Small sinkholes will be difficult to find due to aeolian weathering and remote sensor instrumental resolution Small sinkholes will be difficult to find due to aeolian weathering and remote sensor instrumental resolution Discussion Possible sinkholes have been found in Kasei Vallis on Lunae Terra and where an albedo anomaly exists in the outwash plain. Albedo anomalies also occur in the outflow channels and/or outwash plains of Tiu, Simud, Mawrth, Ares, Lobo, and Shalbatana Valles. We have also successfully imported PDS formatted color Viking Data into a 3D GIS map. We will now be able to overlay PDS data onto this map allowing us to create a 3D digital elevation model of the entire planet superimposed on top of a geographic map. Conclusions and Future Work We have identified three other areas of interest in the search for sinkholes on Mars. Solus Planum, contains depressions similar to solution vallies (Figure 3) Eastern Tharsis, source of the Circum-Chryse outflow channels, contains large areas of chaotic terrain, attributed to the collapse of subterranean caverns. Hellas Crater/Utopia Planitiae: a crater cut by channels having anomalous depressions said to be created by the settling of large blocks of ice Fig. 3. Solus Planum: From the European Space Agency At this point, only Viking data has been introduced into the GIS atlas. The next step will be to incorporate Mars Orbiter Laser Altimeter (MOLA) data, followed by higher resolution imagery from the Mars Global Surveyor and Odyssey. Continued searches for sinkholes and albedo anomalies is necessary in all of the study areas. An additional research project could be to determine whether the volume of evaporites dissolved from the depressions identified as sinkhole is sufficient to create the observed albedo anomalies. Martian Depressions Implications for Large Scale Evaporite Deposits Zackery E. Smith, Jason A. Tullis, Kenneth F. Steele Arkansas Center for Space and Planetary Science, University of Arkansas, Fayetteville, Arkansas, a) PDS formatted Color Viking Data imported into a GIS atlas, with the study area boxed in red. Figure 1 MethodsProcedures Identify study area and guidelines to distinguish between impact, volcanic and sinkhole features Acquire remote sensor data from Mars Global Surveyor and incorporate into GIS atlas Sinkholes Occurring in Outflow Channels Beds will: Be non symmetric Be deeper on the upstream side The outwash plains will have albedo anomalies The length to width ratio will be lower where the flow rates are lowerReferences Bridges, J. C. and Grady, M. M.: Evaporite mineral assemblages in the nakhlite (martian) meteorites. Earth Planet. Sci. Lett., vol. 176, no. 3-4, nakhlite (martian) meteorites. Earth Planet. Sci. Lett., vol. 176, no. 3-4, 2000, pp , pp Costard, F. M. and Kargel, J. S.: Outwash plains and thermokarst on Mars. Icarus, vol. 114, no. 1, 1995, pp Mars. Icarus, vol. 114, no. 1, 1995, pp Feldman, W. C.: 65th annual meeting of the Meteoritical Society. Paul H. Warren, ed., Meteoritical Society, Warren, ed., Meteoritical Society, Rodriguez, J. A. P.; Sasaki, S.; Dohm, J. M.; Tanaka, K. L.; Miyamoto, H.; Baker, V. R.; Skinner, J. A.,Jr; Komatsu, G.; Fairen, A. G.; and Ferris, J. Baker, V. R.; Skinner, J. A.,Jr; Komatsu, G.; Fairen, A. G.; and Ferris, J. Workshop on Hemispheres apart; the origin and modification of the Workshop on Hemispheres apart; the origin and modification of the Martian crustal dichotomy Sept Thomas R. Watters, Patrick J. Martian crustal dichotomy Sept Thomas R. Watters, Patrick J. McGovern, convener and convener, eds., Lunar and Planetary Institute, McGovern, convener and convener, eds., Lunar and Planetary Institute, b) Possible sinkholes in Kasei Vallis, Lunae Planum, from MGS MOLA mapping data