First Landing Site Workshop for MER 2003 9014.pdf

TES HEMATITE LANDING SITES IN SINUS MERIDIANI FOR 2003 MARS EXPLORATION ROVER. E. Noreen1, K. L. Tanaka2, and M. G. Chapman2, 1Cal. State Univ. at Los Angeles, 2460 Meadow Valley Terrace, Los Angeles CA 90039 ([email protected]), 2USGS, 2255 N. Gemini Dr, Flagstaff, AZ 86001-1600.

Introduction: The Thermal Emission Spectrometer shows that the SM sites are relatively free of dust, in- (TES) on the Mars Global Surveyor (MGS) has de- ferred from their relatively high thermal inertia (7-8 x tected large concentrations of bulk crystalline hematite 10-3 cal cm-2 s-0.5 K-1.) within the western equatorial region of Mars. The With engineering requirements [6] for safety met, hematite represents a unique and enigmatic spectral we favor a landing site with high concentrations of signature as one of surface rock distinct from basalt or hematite. TM23B, and to a lesser extent TM10A, are basaltic andesite. Analysis of the spectral data also therefore favored due to their having significant con- suggests that the hematite grains are axis-oriented [1], centrations of hematite evident in the TES data. increasing the mystery. TM23B more than meets all of the engineering re- The largest accumulation of hematite has been quirements and has a very high concentration of hema- found within Sinus Meridiani (SM) centered near 2°S tite, low total rock coverage (6-9%), and a very gentle latitude between 0 and 5°W longitude covering an area slope over the ellipse. The only drawback to TM23B >500 km2 [2]. Within the hematite area in SM there is the elevation (-1.4 km) being close to the required - are several locations suitable as landing sites for the 1.3 km required for safe atmospheric entry. TM10A, 2003 Mars Exploration Rover (MER). while being well below the required elevation, has a This area has been proposed as a candidate for a higher rock coverage and slightly lower hematite con- landing site before because of its hematite signature centration, which may hinder the pursuit of the science [2,3], and our further analysis indicates even more pos- objectives. Based on the above, TM23B is the pre- sible origins and implications for its presence. In SM ferred landing site for SM. and other areas of hematite, we find direct associations Regional Geologic Context of Hematite: The with fluvial/groundwater and volcanic geomorphology hematite signatures have been found on several differ- that may be indicative of the formative processes. ent geologic units. In SM the hematite is confined to Given the generally bland mineralogic landscape of unit Npl2, a subdued cratered unit thought to be thin Mars, the concentrated crystalline hematite locales are interbedded lava flows or eolian deposits partly bury- the only known areas in which we confidently expect to ing weathered cratered terrain [7]. At a larger scale find rock and mineral types dissimilar to that of the the subdued cratered unit was remapped as unit sm [8], Viking and Pathfinder landing sites [3]. a smooth, layered friable surface variously interpreted Areal Extent of Hematite: Although SM has the as eolian/volcanic deposits [7], paleopolar deposits, largest signature of hematite, numerous other occur- and wind eroded sedimentary deposits [8]. rences have been found in the equatorial region, in- The other, smaller occurrences of hematite appear cluding: Aram Chaos [4], Ares Valles [5], Margaritifer on units Hch, Hcht, Hvl, and Avf [7]. In central VM Chaos, in the interior layered deposits within central the hematite is confined to a single unit, Airs, inter- Valles Marineris (VM) [5] and Eos Chasma [5]. The preted to be eolian deposits or airfall tuff [9]. High- hematite is restricted to a ~1200 km band trending resolution MOC images show that the hematite in cen- N80°E from VM to SM. The confinement of the tral VM occurs within a unit similar in appearance to hematite to one relatively linear region rather than dis- the hematite area in SM (SM- M0400568, M0300764; persed planetwide suggests that all of the bulk crystal- VM- M0201705.) line hematite may have formed by the same process. MOLA data revealed that the occurrences of hema- Proposed Landing Sites: We favor four landing tite exist in a variety of topographic terrains. Within sites within SM: TM22B, TM23B, TM10A, TM11A unit sm it occurs on a gentle slope downtrending to the [6, Table 1]. These sites all are below the -1.3 km NW; in the eastern area of sm a high concentration is Mars Orbital Laser Altimeter (MOLA) geoid required on a local topographic high. In Aram Chaos it occurs for safe atmospheric entry. MOLA data also show that on the floor of the eroded crater in between small me- they are all are on gentle slopes of less than one degree. sas. In VM and the remaining areas it occurs on rela- MGS Mars Orbital Camera (MOC) context and high- tively gentle slopes and troughs. resolution images (see images listed in Table 1) show a In many areas the hematite is associated with vol- lack of fresh craters within SM. TES data shows that canic features. TES data shows an intimate relation- the ellipses of the sites are relatively hazard free seen ship between the hematite and possible basalts seen in in the low total rock coverage (>11%.) TES also data basaltic spectral compositions found within or sur- rounding the hematite areas [10]. Within central VM First Landing Site Workshop for MER 2003 9014.pdf

TES HEMATITE LANDING SITES FOR 2003 MER: NOREEN, E.1, TANAKA, K2, CHAPMAN, M2

most of the hematite signatures are found adjacent to ment of volcanic materials, based on the volcanic asso- unit Ahd, a unit interpreted to be young mafic volcanic ciations and geomorphology of SM and VM. material [9]. One occurrence in central VM is ~2 km Potential Instrument Utilization at SM Sites: upslope from a feature interpreted to be a caldera [9]. Each instrument on the rover will be brought to bear on Within SM, unit sm appears consistent with ignimbrite the question of the hematite formation in the western deposits, based on localized layering and mantling of equatorial region of Mars as well as the general geol- topography, and numerous mounds that can be inter- ogy of the landing site. They will be utilized to this preted as fumarolic [3]. end in the following ways: (1) The PanCam will take All of the hematite areas show some evidence of panoramic images to focus the search for hematite- near-surface water activity in nearby fluvial, ground- bearing rocks and visually describe their geologic water, or lacustrine features. South of unit sm there are context. (2) The Rock Abrasion Tool will expose fresh extensive ancient channels within hc, a heavily cratered surfaces on rocks for study. (3) The Miniature Ther- unit, that terminate at the contact of the units [8,3]. mal Emission Spectrometer will gather minerologic

Table 1: Selected hematite landing sites for 2003 Mars Exploration Rovers Site Lat. (°) Long. (°) Elev. (km) Geologic units [7,8] MOC high-resolution images TM22B -3.2 7.1 -1.7 Npl2, sm SP240604, M0300371 TM23B -3.4 3.1 -1.4 Npl2, sm M0403468, M0200446, M0002022, M0002021, M0204225, M0401900 TM10A -2.2 6.6 -1.7 Npl2, sm M0001660, M0301632, M0201539 TM11A -3.4 6.9 -1.6 Npl2, sm SP240604, M0300371

Directly northeast of unit sm, in MOC image information at an outcrop scale of the landing area fa- M0401289, there is a 1-km-diameter feature that could cilitating the search for hematite host rocks at a finer be interpreted as thermokarstic or lacustrine. Aram scale than MGS-TES. (4) The Mössbauer Spectrome- Chaos contains chaotic terrain, possibly caused by ter will gather information on the oxidation states of near-surface water activity. VM is the source area for iron-bearing minerals, which will determine the extent the massive outflow channels in the region. of alteration, if any, in the hematite host rocks. (5) The Possible Formation Processes: Using the spectral, Alpha Proton X-Ray Spectrometer will determine the geologic/geomorphic and topographic relationships, we composition of rocks and soils in the landing area and are able to develop some constraints on the possible will be able to classify the hematite host rock type. (6) formation processes. Spectral evidence indicates that The Microscopic Imager will obtain extremely high the grains are large (>=10 microns) [2] and axis ori- resolution images of rocks and soils which will give ented [1], limiting the formational processes to those clues to the formation of the hematite and may deter- that can produce the preferred growth and size. Al- mine the nature of the alignment of the hematite grains. though all hematite sites have possible lacustrine fea- References: [1] Lane, M. D. et. al., (2000) LPSC tures nearby, the topography of unit sm indicates that XXXI. [2] Christensen, P.R. et. al. (2000) JGR,105, the hematite, if geologically recent, did not form in 9623-9642. [3] Chapman M. G. (1999) 2nd Mars Sur- standing water. The topography of SM also shows that veyor 2001 Landing Site Workshop. [4] Christensen, a metamorphic origin of the hematite, i.e. schistose P.R. et. al. LPSC XXXI,. [5] Noreen, E. et. al. (2000) hematite, is unlikely, as it does not reflect the necessary Mars Tharsis Workshop; [6] Golombek, M. and range of elevation required to produce an overburden Parker, T. (2000) MER Engineering Constraints and pressure that would produce re-crystallization of nano- Potential Landing Sites Memo. [7] Scott, D. H., and phase hematite and orientation of the resulting grains. Tanaka, K.L. (1986) USGS Map I-1802-A. [8] Edgett, Using the above constraints to exclude, at least K.S., and Parker, T.J., (1997) GRL 24, 2897-2900. [9] tentatively, several formation processes, those that re- Lucchitta, B.K. (1999) USGS Map I-2568; [10] Ban- main become more probable. The remaining processes field, J. L. (10/2000) TES Team Member. Personal that fit all available data are: hydrothermal alteration or Comm. replacement of a parent rock with an existing orienta- tion of minerals, thermal oxidation of magnetite–rich lavas [4], and primary mineralization within the cool- ing unit of an ignimbrite [3,5]. We favor a volcano- genic formation, either mineralization within the welded zone of an ignimbrite or hydrothermal enrich-