44th Lunar and Planetary Science Conference (2013) 1363.pdf

COMPOSITIONS DETERMINED BY CHEMCAM ALONG CURIOSITY’S TRAVERSE FROM BRADBURY STATION TO GLENELG IN GALE CRATER, MARS R.C. Wiens1, S. Maurice2, V. Sautter3, D. Blaney4, N. Bridges5, B. Clark6, S. Clegg1, G. Dromart7, C. D’Uston3, C. Fabre8, O. Gasnault3, K. Herkenhoff9, Y. Langevin10, N. Mangold11, P. Mauchien12, C. McKay13, H. Newsom14, D. Vaniman15, R. Ander- son9, J. Baroukh16, B. Barraclough15, S. Bender15, G. Berger17, J. Blank18, A. Cousin2, A. Cros2, L. Deflores4, D. Delapp1, C. Donny16, O. Forni2, B. Gondet10, P. Guillemot16, S. Johnstone1, J.-L. Lacour12, V. Lafaille16, N. Lanza1, J. Lasue2, S. Le Mouelic11, E. Lewin19, E. Lorigny16, N. Melikechi20, P.-Y. Meslin2, A. Mezzacappa20, T. Nelson1, A. Ollila14, R. Perez16, P. Pinet2, M. Saccoccio16, S. Schröder2, J.-B. Sirven12, R. Tokar15, M. Toplis2, C. Yana16, M.D. Dyar21, B. Ehlmann22, J. Johnson5, R. Leveille23, J. Moores24, J. Bridges25, M.R. Fisk26, J. Grotzinger22, and the MSL Science Team (1LANL; [email protected], 2IRAP/CNRS, 3MNHN,4JPL/Caltech, 5APL/JHU, 6SSI, 7Univ. Lyon, 8Univ. Lorraine, 9USGS, 10Univ. Paris-Sud, 11LPGN, 12CEA, 13NASA Ames, 14UNM, 15PSI, 16CNES, 17IRAP/CNRS, 18BAERI, 19U. Grenoble, 20Delaware State U., 21Mt. Holyoke College, 22Caltech, 23CSA, 24U. Western Ontario, 25U. Leicester, 26Oregon State U.) Introduction: The Mars Science Laboratory “Cu- most observations consisting of a linear 5-point raster riosity” rover landed at -4.59, 137.44° on a hummocky or a 3x3 grid. terrain considered to be part of an alluvial fan below Compositions Along the Traverse: All major el- Peace Vallis in Gale crater, Mars. In the first three ements were regularly reported, along with selected months after landing Curiosity traveled east and minor and trace elements, including H (qualitative), Li, stopped at a location called Rocknest where it per- Mn, Cr, Ti, Rb, Sr, and Ba. Figure 2 shows the mean formed first-time in-situ analysis of soil. From sol thir- SiO2 and Fe2O3T compositions from each observation teen on, the ChemCam instrument suite performed along the traverse. The overall pattern shows highly compositional and imaging analyses of rocks and soils variable SiO2 contents in the hummocky region near along the route. This presentation gives a composition- the Bradbury Landing site. This was true for both rocks al overview of the traverse. More details of the obser- and soil measurements, and is interpreted as a result of vations can be found in Maurice et al. [1] and a number sampling varying individual minerals in coarse-grained of other presentations. heterogeneous float rocks and pebbles encountered Traverse Overview: Figure 1 shows a map of the within soils at the site. Images of soils near the landing traverse, with way points marked, and with many of the site show abundant pebbles (Fig. 3a), consistent with ChemCam observations indicated. The zone of disturb- the highly variable SiO2 contents. ChemCam observa- ance from the descent stage thrusters can be seen as tions show that soils are clearly hydrated [3], consistent darker material around the Bradbury Landing site, and with SAM [4] and DAN [5] results at different scales. its approximate boundary is marked in the figure by a The SiO2 contents of the float rocks observed by dashed white line. Within this zone most of the rocks ChemCam near the landing site ranged from the mid were relatively clear of dust, providing unique imaging 40% to that expected for alkali feldspars (upper 60s). opportunities. The terrain in this region is described as The highest SiO2 contents could indicate the presence hummocky material and has abundant gravel (small of quartz, consistent with ~2% quartz tentatively identi- pebbles of various shapes, sizes, and colors) with occa- fied in CheMin XRD spectra of soil [6]. Images of the- sional float rocks and conglomerates which appeared to se rocks (e.g., Fig. 3c and Mastcam images) suggest comprise the bedrock in this region. Between sol ~45 highly porphyritic textures. One of the conglomerates and 50, marked on Fig. 1 by Jake Matijevic and (Link) was observed by ChemCam [7]. Its clasts had a Akaitcho, the first aeolian ripples began to be seen, and range of SiO2 compositions consistent with loose peb- gravel and conglomerate gave way to finer-grained ble compositions in the area. bedrock as observed by imaging and confirmed by a As Curiosity traversed beyond Anton both soils and significant reduction in the ChemCam compositional rocks showed changes (dashed red lines, Figs. 1, 2). standard deviation between observation points of the The occurrence of higher SiO2 compositions became same rock. This correlation between grain size and rare (though still occasional in the soils). Aeolian drifts compositional standard deviation has been demonstrat- were encountered (Fig. 3b) and pebbles became much ed in the laboratory [2]. less common [8]. Fine soil after this transition regis- Description of Observations: Each ChemCam tered SiO2 abundances consistently in the mid-40 wt. % LIBS observation covers a spot between 350 and 550 range, as shown by Akaitcho, Epworth, Schmutz, Ken- µm diameter. Depending on grain size, individual ob- yon, and other samples (Fig. 2). servations generally represent combinations of individ- After the transition, rocks were finer grained and/or ual mineral grains rather than whole rock compositions. more homogeneous, as indicated by reduced standard Each observation point is an average of ~25 coincident deviations between repeat ChemCam observations of spectra, sampling into the rock or soil. The first five the same rock, particularly noticeable for Bath- laser shots are usually ignored, as they are contaminat- urst_Inlet. Iron compositions of these rocks increased ed by dust. Each target (rock or soil) had between one and were generally Fe2O3T > 20 wt %, with some rocks and 30 observation points. Single observation points showing significantly higher iron [9], e.g., Rocknest3, were used only at the beginning of the mission, with Rocknest6, Pearson, Snare, and Walsh (Fig. 2; Et_Then, analyzed by APXS and showing the highest 44th Lunar and Planetary Science Conference (2013) 1363.pdf

iron, with Fe2O3T ~31% [10], was not observed by Acknowledgement: This work was supported by the ChemCam). An anticorrelation between SiO2 and CaO NASA Mars Program Office and by CNES. was observed among averages of all rocks in the area, References: [1] Maurice S. et al. [2] Cousin A. as well as between individual observations of certain (2012) JGR Planets., 117, E10002, doi: rocks (e.g., Pearson) and soils (e.g. Epworth) [11]. 10.1029/2012JE004132. [3] Meslin P.-Y. et al. [4] Archer CheMin analyses are expected to clarify the origin of et al. [5] Hardgrove C. et al. [6] Blake et al. [7] Mangold the rocks in this area. N. et al. [8] Williams R. et al. [9] Sautter V. et al. [10] Overall, ChemCam shows a clear capability, not Gellert et al. [11] Clegg et al. [1,3-11] all (2013), this only to characterize fine features (e.g., [11]) but also meeting. for area compositional and morphological surveys.

Fig. 1. Curiosity rover traverse map for the first 100 sols, overlaid on a HiRISE image (NASA/JPL-Caltech/U. AZ).

Fig. 2. Preliminary SiO2 and Fe2O3T abundances of all ChemCam observations in sols 13-100.

Fig. 3. ChemCam RMI images: Kam (a) and Akaitcho (b) soils showing the transition from the hummocky terrain displaying abundant pebbles and occasional conglomerate outcrops, to the region near Glenelg characterized mostly by bedrock and aeolian deposits. Heavily weathered Stark (c), a porphyritic rock near Bradbury, and Rocknest3 (d) observed in the latter part of the traverse.