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Apxs Measurements Along the Msl Traverse at Gale Crater, Mars Eighth International Conference on Mars (2014) 1327.pdf APXS MEASUREMENTS ALONG THE MSL TRAVERSE AT GALE CRATER, MARS. R.Gellert1, J.A.Berger2, N.Boyd1, J.L.Campbell1, B.Elliott3, A.Fairén4, P.L.King5,1, L.Leshin6, B.Pavri7, G.M. Perrett1, I.Pradler1, M.Schmidt8, S.W.Squyres4, L.Thompson3, S.VanBommel1, A.S.Yen7. 1University of Guelph (Guelph, ON, N1G2W1, Canada; [email protected]), 2Univ. of Western Ontario, London, ON, 3Univ. of New Bruns- wick, Fredericton, NB, 4Cornell Univ., Ithaca, NY, 5Australian National Univ., Canberra, Australia, 6Rensselaer Polytechnic Institute, Troy, NY, 7Jet Propulsion Lab, Pasadena, CA, 8Brock Univ., St. Catharines, ON Introduction: The MSL Alpha-Particle-X-ray- encountered. Dust, possibly covering the real bulk Spectrometer (APXS) [1] is the third generation of properties, will typically skew the ratio towards 1. chemical in-situ instruments of its kind onboard a NASA Mars rover. At Gale Crater it measured so far S048 (JakeMatijevic) S054 (Bathurst) about 100 samples in the first 590 sols along the trav- 10 S091 (ET_then2) erse from the landing site at Bradbury Rise over Yel- 169 (WerneckeBrushed) lowknifeBay (YKB) towards Mount Sharp. APXS Performance: The APXS measures and quantifies typically 16 major, minor and trace ele- ments using x-ray spectroscopy. Compared to the 1 MER instruments the MSL APXS is about 5-10 times faster and allows high quality data acquisition during Portage to ratio most of the Martian day. With an improved FWHM from ~ 170 eV to 140 eV and higher signal to back- ground ratio than MER, 20 minute spectra on MSL 0.1 deliver similar statistical uncertainties and detection Na Mg Al Si P S Cl K Ca Ti Cr Mn Fe Ni Zn Br Ga Ge limits as overnight MER data. APXS data allow de- Figure 2: Distinct rock Chemistry encountered at Gale. tailed comparison and correlation of Gale crater and Distinct Rock Classes: Fig. 2 shows the distinct the MER landing sites. characteristics of the 4 major rock types found at Gale so far. Only types that represent at least 2 very similar 100 rocks are shown. approximate sensitivity: MSL to MER x3 x6 x 10 JakeM has high Na, Al, K and low Mg, Fe, Cr and Basaltic Soils 10 Gale S531 Ni and was identified being similar in composition to Gusev S0047 terrestrial Mugearites [2]. While being usually en- countered as floats, also conglomerates at Darwin 1 show similar characteristics. Bathurst class is rich in K, Fe and Zn and is typically found in fine grained counts/s 0.1 sandstones from Rocknest to Kimberley. Wernecke is one sample representative for the YKB outcrop, where 0.01 up to 30% clays were identified by Chemin [3]. It has similar major chemistry as the soil or average Mars, 1E-3 with clear enrichments in Cl, Ni, Zn and Ge and a 0 2 4 6 8 10 12 14 16 18 20 22 24 distinct higher Fe/Mn ratio than established for igne- Energy [keV] ous rocks or soils on MER or in SNCs [4]. Et_Then was first a singular occurrence of a dark, fine-grained Figure 1: APXS spectra of the typical Martian soils rock that had to be measured with a very high stand- for Gale and Gusev. off. Its unusual composition, having high FeO up to APXS results at Gale Crater: Similarly to MER 27 wt %, low Mg and Cr and in particular elevated Ga the major chemistry can be used to group similar of about 70 ppm, made it somewhat an outlier at Gale rocks, establish geologic relationship or diagenetic until the sample Secure showed a very similar trait. connection between different members. In Gale so far Secure is thought to be representative of the massive several distinct classes of rocks have been identified dark capping unit. based on their APXS chemistry. A suitable way to plot One advantage of the APXS characterization is the the chemical trends and distinctions is to ratio the high precision of the instrument over the whole range composition to the first MSL soil Portage, fig. 2. A of the elements. Fig. 3 shows near identical character- logarithmic scale allows to capture the large variations istics of samples encountered several kilometers apart Eighth International Conference on Mars (2014) 1327.pdf that allows to deduce possible connections about their of 2 drill holes are remarkably constant, with the ex- origin and possible diagenesis. emption of CaSO4 rich vein material (Mavor) and Mg, Fe and Cl enriched raised ridges (McGrath ras- 10 ter)[4]. Brushed surfaces showed mainly a significant S048 (JakeMatijevic) S503 (Morehouse_RP) decrease in Sulfur, exposing a very low SO3 content S091 (ET_then2) 560 (Secure) as low as 1%. Nearly all samples at Gale, except YKB show a distinct variable enrichment in K2O over the ~ 0.5wt % of Martian soils and dust. 1 442 (Rensselaer) 583 (SquareTop5) 10 54 (Bathurst) ratio to Portage to ratio 0.1 Na Mg Al Si P S Cl K Ca Ti Cr Mn Fe Ni Zn Br Ga Ge Portage to ratio 1 Figure 3: Near identical members of the JakeM and Et_Then class. Trends during the Traverse: Plotting the ele- ments along the traverse (sols) can reveal geologic relationships and boundaries and can be correlated to Na Mg Al Si P S Cl K Ca Ti Cr Mn Fe Ni Zn Br Ga Ge geological maps. Fig 4 plots Fe together with the mi- Figure 5: SquareTop compared to Cooperstown and nor and trace elements Cr, Ni and Zn along the trav- Bathurst erse. Similar trends can be seen for other major ele- ments due to the specific character of the various rock As of sol 590, Curiosity reached the next way- classes. point Kimberley, where detailed in-situ investigations The float rocks of JakeM type and Bathurst and and drill samples for SAM and Chemin are planned. The first results at Kimberley indicate that the fine 10 grained sandstone is similar in composition to the Rocknest YellowKnifeBay Darwin Coopers- Kimberley town Bathurst type. While YKB had similarly high Fe as Bathurst, the Fe/Mn ratio of Bathurst is typically not as elevated as in YKB, indicating that Bathurst is less enriched in Fe3+. The analytical instrument SAM and 1 Chemin might shed light especially on the remarkably elevated Potassium, as well as the high Fe, which pos- sibly acts as a cement. ratio to Portage to ratio Cr2O3 Ni Zn 0.1 References: [1] Gellert et al. (2009) LPSC, #2364, [2] Stolper et al. (2013) Science , 1239463, [3] Vaniman 0 100 200 300 400 500 600 et al. (2013) Science, 1243480, [4] McLennan et al. sol (2013) Science, 1244734 Figure 4: Trends along the traverse. Acknowledgements: The MSL APXS is managed Et_then type rocks are wide spread in Gale. Conglom- and financed by the Canadian Space Agency, with erates likely consist of JakeM like constituents meas- MDA as prime contractor to build the instrument. ured with the APXS at the way point Darwin. Curiosi- Science team funding is provided by CSA and NASA. ty spent sols ~150 to 300 exploring YKB, where the We appreciate and acknowledge the unwavering sup- compositions of ~20 in-situ spots as well as the fines port of dedicated engineers at JPL during operations. .
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