Analogue Sites for Mars Missions (2011)

6014.pdf

THE UBEHEBE VOLCANIC FIELD (DEATH VALLEY, CA): A HIGH-FIDELITY ANALOG SITE SUPPORTING MSL11 INTEGRATED SCIENCE MISSION GOALS. CLAY CYCLE AND HABITABILITY POTENTIAL UNDER ARID HYDROCLIMATIC CONDITIONS. R. Bonaccorsi(1-2), C. P. McKay(1), G. Valdre (3), and D. Willson(4)
Space Science & Astrobiology Division, MS-245-3 NASA Ames Research Center, Moffett Field, CA (2) 94035, USA (rosalba.bonaccorsi-1@nasa.gov); SETI Institute, Mountain View, CA 94043, USA; (3) (4) Department of Earth and Geo-Environmental Sciences, University of Bologna, Italy; The Mars Society Australia, P.O. Box 327 Clifton Hill 3068.
Introduction: The Mars Science Laboratory (MSL) mission will primarily search for potentially habitable, ancient geological environments, as a preliminary step to future life detection e.g., the ESA/US 2018 Pasteur ExoMars, and sample return missions. All MSL site candidates include hydrated clay minerals, or phyllosilicates, and have been evaluated by context, diversity, habitability, and preservation potential of organics. Phyllosilicates are unambiguous indicators of past aqueous activity on Mars, and of particular interest due to their high preservation potential. MSL science goals will require a highly-integrated science approach simultaneously involving: a) the understanding of role of (liquid) water/climate, and time scales involved in weathering processes and conducive to life (as we know it); and b) the identification of geological targets enabling concentration as well as preservation of biological and nonbiological organics. In the above context, we have identified high-fidelity analog sites at the Ubehebe Volcanic Field (UVF) (Death Valley National Park, California, USA), Figure 1. Overall, the UVF combines multiple analogies (geological, geomorphologic, mineralogical, and hydro-climatic) of setting and processes argued for MSL sites and other Martian sites.
Figure 1. Aerial view (~2 km by ~2 km) out of 25 km2 including target features of the UVF at a spatial scale (few hundreds of meters to 4-5 km traverse) reachable by a rover. The Ubehebe Crater is centered at 37035N, 1172701W at an elevation of ~655-meters. Road access is on the left-upper corner. The UVF comprises three main subsystems, or areas of prime science interest, each one with a specific, and/or general feature relevant to MSL sites (underlined). 1. The Ubehebe Crater (UC), the largest in the area, is ~0.8 km-wide, 150 to 237 m-deep, and ~2 to 4-7 thousand years old. The exposed wall lithology consists of hundreds meters-thick
heterogeneous fluvial deposit (e.g., reddish mudstone), and a rhyolitic tuff outcrop uniquely localized. They are overlain by thinly bedded/laminated pyroclastic deposits (pumice and basaltic ash) of Recent age. Wall deposits supply weatherable material to intra-crater fill deposit rich in Al-smectites (Mawrth/ Eberswalde) and of unknown thickness. 2) The Southern Craters Group (SCG) has a shallow drainage and more extended alluvial features (Holden Crater) with respect to the other sites; and 3) the Little Hebe (LH) is a small spatter cone, which rim consists of molten scoriaceous lava, partially oxidized (hematite), layered sulfates unique at this site, and clays (mineralogical variability/ Gale Crater). A comprehensive set of integrated investigations can be conducted at each location to address general and specific mission goals and to test science-driven hypotheses (multiple Science Merit Related to Mission Objective). The UVF is a cratered terrain (caldera) formed by subsequent phreatomagmatic eruptions 27 thousands years ago and presents a well-distinct drainage system. This enables direct measurement and quantification of sedimentary processes, moisture conditions and clay formation from a unique source, or a few well-identifiable ones. The UVF geology is relatively young oldest formations are of Miocene age - with respect to that argued for the MSL sites (e.g., Noachian-Hesperian). As such, the analogy refers to a past wetter/ warmer Mars rather than to the present dry and cold Mars, or to geological age. UVF developed under desert conditions and timescale (~103 to 104 years to present), which are analog of hydro-climatic conditions and timescale inferred by some for the Noachian Hesperian transition i.e., characterized by episodic (maybe seasonal) long-term arid-semiarid rainfall (~104 years) [1]. Mission Elements: Understanding time scales of sediment weathering in function of liquid water exposure and subsequent formation of clays from geologically different parent materials. Hypotheses: Are Al-smectites produced in situ, or are they (wash-out) from elsewhere? UVF includes a diversified set of sedimentary analog environments (fluvial, alluvial, lacustrine, and pyroclastic) at landing sites. Mission Element: Identification of the best target for concentration/ preservation of organics. Main question: How do different depositional setting will influence habitability and preservation potential? UVF subsystems account for a high mineralogical variability: Within 1 km2 presence of different types of phyllosilicates (Marwth) and/ or more mineral types (clays, Fe-oxides, detrital silicates, sulfates, and carbonates). Mission Element: Prioritizing search for organics/habitable environments by the CheMin-SAM suite based on non-contact, remote information from ChemCam. Hypotheses: Evaluation of habitability and preservation potential in clay-rich vs. nonclay background materials (follow the minerals and the water!). Current Investigations. To address prime science questions we have been focusing on the Ubehebe Crater fill deposit (mud pond). Here we can test hypotheses centered on recycling vs. neo-formation of clay minerals as analog processes of forming smectites on Mars. Preliminary Q&A, based on a still limited set of observations, follows below. 1. Are currently arid hydro-climatic conditions sufficient to form smectites from recycled sedimentary components? Yes: up to hundreds meters of fine-grained sediment can rapidly accumulate and weather to Alphyllosilicates under arid conditions (mm/y Rainfall over year 2004 to date) similar to those argued for the NoachianHesperian transition [1]. The bulk mineralogical composition (XRD data) of red mudstones (N=6) from wall materials (fluvial) is typically detrital (major amounts of quartz, carbonates, plagioclase, k-feldspar), and minor inherited clays (chlorite, muscovite/illite, and possible smectites). In contrast, the intracrater fill (mud ~99wt.% avg., N=5) contains higher amounts of primary products from weathering of glass and feldspars to Ca-montmorillonite (Al-smectite). Al-smectite-bearing

horizons at Mawrth Vallis [2-4] may represent a late sedimentary, or altered pyroclastic deposit [5] draping the topography [6-7], which appears to be the case for the Ubehebe Crater. In Water Year (WY) 2010 two extreme rainfall events delivered 75 mm rain in about 7 days (January and February 2010). We assume that from the two events combined, the crater bottom received up to 3 - 5 mm average (N=7) silty-clay from direct erosion of the rhyolitic tuff outcrop (surface area of 4,263 m2). A major contribution ~11.6 1.7 mm (N=38) was from wall (surface ~55,062 m2). By assuming a constant average sediment rate of ~1 cm/y since the crater formed (2-10 thousands years) we can estimate a present-day thickness of about 33 to 167 m-depth. 2. How long does water have to be in contact with surface minerals in these sediments to form smectites? In WY 2010 the two rainfall events formed a 20 cm-deep pond (volume 286 m3), conditions not reproduced in WY 2011, yet. Pond moisture varies from 2-3 wt.% water content in summer/dry conditions to ~50-55 wt.% (saturated conditions). Other Investigations: We have been focusing [8-10] on distinguishing preservation from habitability potential. Particularly in testing (microbial) hypotheses in clay-rich vs. nonclay (background) materials: 1) Clays are environments relatively low in living microbial content. 2) Clays can well preserve organic remains of microbe. Detailed explanation is behind the scope of this abstract and will be provided as the opportunity arises. Table 1: Scientific merit of the analogue site to MSL/ExoMars missions
Site Name Prime Science Questions 1 Distance of Science Targets from nearest road or airstrip Environmental features Previous studies at analogue site Primary Landing Site Target Ubehebe Crater and Ubehebe Volcanic Field See main text above (this page). Ubehebe Crater Bottom 10-15 min walk 0.3 km to park lot Little Hebe 20 min-walk 1.5 km to park lot Southern Crater Group 2 km to park lot Max temp: Air 52C, Min temp: -10C Precipitation: see main text. Vegetation coverage: 0 to 20-50% bush, depending on season and location. [8-10] MSL: e.g., Mawrth, Eberswalde. Any smectite-rich area of Mars.

Airborne imaging spectrometer and AVIRIS data are available for this site. We have developed a good knowledge of sites and logistics from several years of working at the UVF. The UVF is located within one hour's walk from the service area/parking lot. Safety considerations may arise particularly during the rainfall season, owing to extreme weather (flash flood and storms). The site is easily accessible (paved road) via CA Hwy 190, ~5 miles from the Grapevine Ranger Station (radio station and closest shelter) and it is ~10 miles from the main Station at Scottys Castle (emergency medical services/shelter, radio station). Maintenance assistance for federal vehicles is available during emergencies. Research permits enabling sampling and placement of data loggers have been cleared with the NPS (DEVA-2010-SCI-0027). They fulfill tribal requirements/limitations for activity at the most sacred area to the Timbisha-Shoshone Tribe. At DEVA E/PO activities outlining relevance of the UVF to MSL are planned from March 2011 to prior launch. References: [1] Barnhart, C.J., et al., (2009). J. Geophys. Res. [2] Bishop, J.L., et al., (2008) Science
321, 830-833. [3] Mustard, J.F. et al., (2008) Nature, 454(7202):305-309. [4] McKeown et al., 2009. JGR, 114(52). [5] Tosca, N.J., and Knoll, A.H (2009). LPSC, p. 1538. [6] Wray, J.J., et al., (2008). Geophys. Res. Lett. 35 (2008) p. L12202. [7] Milliken, R. E., and Bish, D.L, (2010) Phil. Mag. 90(17-18):2293-2308. [8] Bonaccorsi, R. et al., 2010 Phil. Mag. 90(17-18):2309-2327; [9] Bonaccorsi, R., (2011) In: Cellular Origin, Life in Extreme Habitats and Astrobiology, Vol. 18. STROMATOLITES: Interaction of Microbes with Sediments. Tewari, V. Seckbach, J. (Eds.). 2011, ISBN: 978-94-007-0396-4, In Press. [10] www.seti.org/meet-our-scientists/rosalba-bonaccorsi.