Lunar and Planetary Science XXIX 1946.pdf SOUTHWESTERN ISIDIS PLANITIA, MARS: A MARS SURVEYOR LANDING SITE at the GEOLOGIC CONTACT between THREE UNITS L. S. Crumpler, New Mexico Museum of Natural History and Science, 1801 Mountain Rd NW, Albuquerque, NM 87104 INTRODUCTION. Mars exploration themes under the Mars Surveyor program include the broad topical The areas of interest have been geologically areas of life, climate, resources, surface age, and mapped digitally at scales up to 1:300K, using atmosphere. The approach includes initial landing specially mosaiked and digitally enhanced Viking and mobility at several sites and, ultimately, sample EDRs. Spectral data [5] were also considered. Two return [1]. A program is underway to identify sites transitions of particular interest occur in the that will enable addressing these goals. This study southwestern margin: (1) Syrtis Major to Isidis evaluates potential Mars Surveyor lander/rover sites Planitia, where lava flows from Syrtis Major meet the on the southwestern margin of the Isidis impact basin Isidis basin plains, and (2) Libya Montes to Isidis, through high-resolution mapping combined with where fluvially modified massifs and valley network remote sensing data. Three sites along the western terrains contact the ridged Isidis plains. Mapping of and southwestern margin of the Isidis Basin have the second area is shown in Figure 1. The proposed been identified for detailed mapping [2]. landing site occurs where these two transitions meet Two sites along the transition between Syrtis and result in a geologic triple point; contacts for three Major and Isidis Planitia have been discussed geologic units, Syrtis Major Planum, Isidis Planitia previously [2]. The discussion in this abstract centers and the Libya Montes, occur here in combination on a third site at 3.4°N and 277.8°W. The proposed with a single large impact crater. site lies at the geologic junction between the MAP DISCUSSION. Eight units are mapped and span sedimentary basins and highlands massifs of the ages from middle Noachian to late Hesperian-early Libya Montes, the intermediate-age lavas of Syrtis Amazonian (Fig. 2): Nm, ancient highland massifs Major Planum, and the late basin-fill materials of interpreted to be heavily eroded Isidis basin ejecta; Isidis Planitia. The proposed landing site is sampling Nf, fluvially dissected foothills and lower slopes of of fluvial sediments deposited at the terminus of one massifs and rolling intermontane plains; Hi, of the highest drainage density areas on Mars. There intermontane and crater-interior plains interpreted as are also realistic opportunities to sample a thick sediments; Hd, plains bearing high density valley stratigraphic section of sediments, examine networks with meandering characteristics; Hv, Syrtis macroscopic fluvial features of sedimentary rocks, Major lava flows, Hk, kobby, Isidis-marginal plains; analyze altered highland materials, and analyze and Hr, plains with ridges and aligned-mounds of the intermediate age lavas derived from Syrtis Major. Isidis basin interior. The site is chosen such that these goals are attainable The proposed site lies in the terminal fan of a with a simple geotraverse of as little as 10 km over large valley network (Fig.3). As a result of late terrain with relatively benign slopes. The proposed incision over a broad area of the fan, a thick section area is a modification of Site C proposed previously of sediments may be examined with a horizontal [2]. geotraverse. Altered crystalline highland rocks occur PROJECT DESCRIPTION. The margins of the Isidis in adjacent hills. Samples intermediate-age Syrtis basin were selected for study because many sites lava flow are also possible as ejecta from the nearby along the margins both fit within engineering crater Syrtis Ee. constraints and address science objectives of the Mars REFERENCES.[1] Mars 2005 Sample Return Workshop, LPI Surveyor program. Of particular importance to Mars Tech Report 97-01; [2] Crumpler, 1997, LPSC XXVIII, 231; [3] Surveyor goals is the fact that the Isidis basin has Grizzaffi and Schultz, 1989, Icarus 77, 358-381; Meyer and Grolier, 1977, U. S. Geol. Survey Misc. Invest. Series Map I- been a topographic sink for volatiles [3], runoff of an 995;[4] Schultz and Britt, 1986, LPSC XVII, 775-776; [5] area of high drainage density [4], and possible Mustard et al., 1993, Jour. Geophys. Res. 98, 3387-3400. subsurface flow and spring emergence [1]. Lunar and Planetary Science XXIX 1946.pdf SW ISIDIS, MARS SURVEYOR LANDING SITE: Crumpler, L. S. Figure 1. Geologic map prepared on digital mosaic base showing the regional setting of the proposed Mars Surveyor landing site (A). Site is located at the terminus of a significant valley network draining the highland massifs on the southwestern margin of the Isidis basin. In addition to the fluvially-laid sediments deposited at the terminus of this valley network, a large impact crater (northwest map) could have distributed intermediate-age lavas of Syrtis Major across the proposed landing site. Figure 3. High resolution view of proposed site showing a Figure 2. N(5 km) crater densities for six of the eight principal traverse route across fluvial sediments at the terminus of a large geologic units. valley network. Lines highlight morphologic features.Merged Viking EDRs 377s77& 78..