https://ntrs.nasa.gov/search.jsp?R=19950009771 2020-06-16T08:53:33+00:00Z View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by NASA Technical Reports Server 24 Mars Pathfinder Landing Sire Workshop knowledge, then they will be more difficult elsewhere where the outliers flanked by younger material within Nepenthes Mensas and questions are unknown. Aeolis Mensas, but such areas are rugged and unsuitable for a safe Conclusions and Site Recommendations: It is tempting to landing. However, parts of western Arabia Terra extend to accept- set the sights for future prospects on many of the additional interest- able elevations and are reasonably smooth. ing areas defined on Mars since the Viking mission and expand the A second strategy is to sample materials at the mouth of an database for ground truth to new and different terrains. This desire outflow channel that drains from the highlands. Channels may should be balanced with the critical need for success in planetary terminate in deltas, alluvial fans, or sheet deposits. For simplicity exploration in general and avoidance of an inconclusive mission these deposits will be refered to as “fans.” Fans provide materials result in particular. An important goal should be learning how to from a large sampling area, and dissected fans offer the advantage operate on Mars and addressing answerable questions. A fmstart of providing a vertical section of exposed stratification that records on the latter can be attained by a new mission to Chryse Planitia in the history of the outflow. the region specified, in which theexisting ground truth of the Viking On first appraisal, any fan at the mouth of a channel draining Lander 1 is used to constrain the engineering choices and to design from highlands offers a potential target, but not all fans offer equal appropriate instrument goals to fully utilize the lander limitations opportunities. Many outflow channels have ponded along their and capabilities. Three proposed sites are indicated on Fig. 1 along length; hence, any sediment carried by the discharge at the mouth is with the currently defined landing ellipses. Site El is most likely to derived only from the last site of ponding [3]. Further, although be similar to VL-1; site E2 is less well constrained and is likely to catastrophic outflows are characterized by high sediment load and differ from VL-1 in some respects; and site E3 is likely to be similar large caliper, the last sediments deposited during waning discharge to VL-1. but incorporates slightly less hazardous, but slightly differ- are generally fine grained. ent terrain. Potential Landing Sites: Potential landing sites include out- References: [ 11 Crumpler L. S. et al. (1994) USGS 1:1 M scale flow channel material at the edge of Chryse Planitia and highland map, submitted. [2] Craddock R. A. et al. (1994) JGR, submitted. materials bordering southern ArnazonisPlanitia. The circum-Chryse [3] Schultz R. A. and FRYH. V. (1990) JGR, 95, 14175. [4] Stock- channels include Kasei Valles into northwest Chryse Planitia; man s. and Frey J. (1993) Eos, 74, 199. Bahram Vallis, Vedra Valles, Maumee Valles, and Ma$ Valles into western Chryse; Shalbatana Vallis into southwest Chryse; N95- 16186 channels draining from Capri and Eos Chasmata into southern Chryse (Simud. Tiu, and Ares Valles); and Mawrth Vallis into A HIGHLAND SAMPLE STRATEGY FOR PATHFINDER. northeast Chryse Planitia. With so many large outflow systems ’), R. A. De Hon, Department of Geosciences, Northeast Louisiana terminating within Chryse Basin, it is probable that any landing site 1I University, Monroe LA 71209, USA. within the basin (including Viking 1 landing site) will be blanketed ( by sediments from catastrophic outflows or outflow sediments re- Mission Constraints: Potential landing sites are confined to worked by eolian activity. Channels in southern Chryse Planitia, latitudes between Oo and 30°N and surfaces below 0 km elevation. originating within Vallis Marineris or chaotic terrain south of Chryse The landing ellipse is lOOx 200 km oriented N74OE. The constraints Planitia, traverse Noachian material before entering the basin, but essentially eliminate the slopes of Elysium Mons, Olympus Mons, they do not provide readily identifiable fans. Tharsis Ridge, Lunae Plaunum, all the southern highlands, and Best Bets: Mawrth Vallis of the Oxia Palus region cuts almost all the Noachian material of Arabia Terra. Those areas that Noachian cratered plateau material, which is interpreted to be remain as potential landing sites are chiefly lowland plains of largely impact breccia of ancient crust [4]. The plateau surface Amazonis Chryse. Isidis. and Elysium Planitiae. bordering the lower reaches of the channel, below 0 and -1 km Siting Strategy: With only two previous Viking landing sites elevation, is one of the few places on Mars where typical highland in widely separate locations, almost any landing will provide new material can be found below 0 km elevation. Three landing sites are data. Viking I landed on Chryse Planitia on a surface that is feasible. One potential site is at the mouth of the channel (29ON. presumed to be Hesperian ridged plains material, which is inter- 21OW); an alternate site is on the plateau surface adjacent to the preted to consist of volcanic flows [ 11. Viking 2 landed on knobby valley (28ON, 18OW);and a third site is south of Mawrth Vallis and material in Utopia Planitia, which is interpreted as eolian and east of Ares Vallis (2ON, 2OW). The highland site adjacent to volcanic materials (21. The large landing ellipse precludes a finely Mawrth Vallis is more likely to contain less surficial cover than the targeted sampling strategy. Several site selection strategies are site east of Ares Vallis. If not covered by surfkial material, highland equally valid. Presumably, Noachian materials are more represen- sites are likely to consist of highly commuted materials; they would tative of the geochemical character of the planet than the volumetri- provide an estimate of the geochemical character of the homog- cally less important surficial flows and sedimentary materials. enized early crust. Any attempt to sample highland material further constrains the The mouth of Maja Canyon (18ON, SOOW), with remnant fan possible landing sites by eliminating areas of Hesperian or Amazo- material cut by late-stage discharges [5,6], offers the best channel nian lavas and sediments. Materials of possible Noachian age are mouth target. The chief constituents here are likely to be detritus primarily located above 0 km elevation and at southem latitudes, from Noachian material of the Xanthe Terra region carried by except for minor occurrences in Arabia Terra and a narrow zone outflow that spilled onto Chryse Planitia following ponding behind along the southern edge of Elysium Planitia. a barrier massif of Noachian basement material. One possible sampling strategy is to sample materials within Pitfalls and Predictions: The large landing ellipse and low those few “highland” terrains that extend to low elevations. Minor resolution of Viking images do not allow assurance that the landing occurrences of Noachian materials are exposed at low elevations as site will contain any particular anticipated material. Extremely LPI Technical Report 94-06 25 localized deposits of young materials are possible in the highlands, Cerberus includes a smooth surface of Late Amazonian fluvial, and mature, winnowed sediments are possible in the plains. Inter- lacustrine, andor volcanic deposits 17-91 and Noachian(?) mesas pretation of chemical anlyses of fan materials without comspond- and knobs of the Tartarus Colles [7]. ing petrologic comparison will be challenging. Dark Material and Source: Dark sand has been transported In all probability, the final choice of a landing site will be a level through and deposited within Cerberus [3,10,11]. Lateral variation lowland within the planatiae. A sedimentary surface of an essen- in sand deposit thickness is probable, with sand filling low areas on tially monomineralic, eolian (sand or loesslike) material or a lacus- and between lava flows. Dark material has blown from east to west trine deposit should not be a surprise. over the lava flows of southern Elysium, perhaps making Cerberus References: [I] Scott D. H. and Tanaka K. L. (1986) USGS similar to the Amboy volcanic field of Southern California. Amboy Misc. Inv. Ser. Map I-1802-A. [2] Greeley R. and Guest J. (1987) has lava flows overlain by windblown sand stripped from an upwind USGS Misc. Inv. Ser. Map 1-1802-8. [3] De Hon R. A. and Pani dry lake [ 121. E. A. (1993)JGR, 98,9129-9138. [4] WilhelmsD. E. (1976)USGS Dark material might be eroded from sediments of the proposed Misc. Inv. Ser. Map 1-895. (51 Rice J. W., this volume. [6]Rice J. W. lacustrine basin [SI east of Cerberus. Alternatively, the sand may and De Hon R. A. (1994) USGS Misc. Inv. Ser. Map I-2432. have avolcanic source, perhaps pyroclastic material from the Elysium volcanos or from eruptions along the Cerberus Rupes fractures. ? - /J N95-16187 Dark material appears to emanate from some Cerberus Rupes frac- / /' . ., \' tures ([ 1 11. Viking image 883A09). Do the fractures expose a layer OPPORTUNITY TO SAMPLE SOMETHING DIFFERENT: of dark material that is now eroding [IO, 1 l]? Did dark material from THE DARK, UNWEATHERED, MAFIC SANDS OF CER- the east fill the fractures. and now is being deflated? Or were the BERUS AND THE PATHFINDER 1997 MARS LANDING. fractures the sites of pyroclastic eruptions? One fracture seen in the K. S. Edgettl, R. B. Singerz. and P. E. Geissler2, 'Department of upper left corner of Viking frame 385823 has a dark, semi-elliptical Geology, Box 87 1404, Arizona State University, Tempe AZ 85287- mantle deposit similar to pyroclastic deposits on the Moon and Io. 1404, USA, *Planetary Image Research Laboratory, Department of Pathfinder Science: Cerberus is large enough that several Planetary Sciences, University of Arizona.