Preliminary Comparison of Soils Within Gale Crater to Those from Gusev Crater and Meridiani Planum

47th Lunar and Planetary Science Conference (2016) 2477.pdf

PRELIMINARY COMPARISON OF SOILS WITHIN GALE CRATER TO THOSE FROM GUSEV CRATER AND MERIDIANI PLANUM. C. D. O’Connell-Cooper1, L.M. Thompson1, J.G. Spray1, J.A. Berger2, E.D. Desouza3, M. Schmidt4, A. Yen5, N.I. Boyd3, R. Gellert3, G. Perrett6, S.J. VanBommel3, and the MSL-APXS Team. 1Planetary & Space Science Centre, University New Brunswick, 2 Bailey Drive, Fredericton, NB, E3A 3B5, Canada, [email protected], 2 Western Univ., London, ON, 3Univ. of Guelph, Guelph, ON, 4Brock Univ., St., Catherines, ON, 5JPL-Caltech, 6Cornell Univ., Ithaca, NY.

Introduction: APXS instrumentation has been variation, and divergence from Portage. FeO, P2O5, used to analyze soils at three separate Martian TiO2, Cr2O3, MnO and Zn are notably depleted, locations: 1. Meridiani Planum (Opportunity, MER); 2. relative to Portage. Gusev Crater (Spirit, MER); 3. Gale Crater (Curiosity, As expected, the Gale soils (red) show the MSL). Previous research has indicated that soils at strongest similarity to Portage. The majority of lighter Gusev and Meridiani are similar in composition and elements, including Na, Al, Si and Ca, as well as Br, may represent a global unit [1]. Comparison to Gale are tightly constrained, showing little variability, soils can further our understanding of the origin and whilst Mg shows some variation. In contrast, S, Cl and evolution of this unit. Whilst a more complete cross K are considerably depleted or elevated, relative to calibration between the three APXS instruments will Portage. Cr, Mn, Fe, Ni and Zn also show variation, require more data from Curiosity, it is possible to although not as pronounced. 2.50 compare soils from the three locations. The MER Meridiani Ratio to Portage Gusev datasets (undisturbed, “dark” soils, max. grain size 100 2.00 Gale μm [1]) used here comprise 6 samples from Meridiani Planum [2, 3] and 24 samples from Gusev Crater [2, 1.50 3]. Gale Crater (undisturbed) soil samples are divided 1.00 into two categories here: Gale Soil (n=10, the main

grouping (including Portage, which is regarded as 0.50 being representative of Average Gale, and is used here 0.00 to ratio abundances for ease of comparison) and Na2O MgO Al2O3 SiO2 P2O5 SO3 Cl K2O CaO TiO2 Cr2O3 MnO FeO Ni Zn Br Bagnold Dunes Soils (from the ongoing Bagnold Fig. 2. Average chemical compositions of samples Dunes Campaign). (Individual Bagnold Dunes samples from Meridiani Planum, Gusev Crater, and Gale BD denoted by ; av=average). Crater, ratioed to Portage. Comparison of soils analyzed by APXS – major elements and Ni, Zn and Br: The ratio of soil Fig. 2 plots the average undisturbed soil analyses from Gale soils and from the basaltic soils at composition (Table 1) for a given category, ratioed to Meridiani and Gusev to Portage (Fig. 1) indicate that Portage. Si, Al and Ca abundances for each soil are soils from all three locations have similar compositions tightly constrained, with little range (Fig. 1, 2; Table with minor differences, e.g., Ni and Br. 1). Si abundances are similar for Gusev and Meridiani, 2.50 Gale Crater Ratio to Portage Gusev Crater but are lower and more varied at Gale. The highest Meridiani Planum 2.00 Al2O3 is seen in the Gusev soils, whilst the Meridiani samples are more similar to the Gale soils (av. 9.12 wt.

1.50 %). Conversely, the Gusev soils have the lowest CaO and FeO contents (Fig. 1, 2). MgO abundances for 1.00 Gale and Gusev soils are similar; Meridiani concentrations are lower. 0.50 K, S and Cl show considerable variation, relative to Portage, in all categories (Fig. 1). Within the Gale 0.00 Na2O MgO Al2O3 SiO2 P2O5 SO3 Cl K2O CaO TiO2 Cr2O3 MnO FeO Ni Zn Br soils, values show two distinct groupings – the bulk of Fig. 1. All analyses ratioed to Portage, showing the the samples (incl. Portage) cluster together, close to variability within an individual category and across averages for Meridiani and Gusev, whilst the second categories, relative to Portage (i.e., Average Gale). cluster (n=3) shows relatively high values for K, S and Cl. The largest range in values for Cl, S and K are seen It can be seen that samples from Meridiani Planum at Gusev; however, the high-value Gale cluster (blue) are less varied than Gale and Gusev (due in part comprises the highest Cl soil values seen on Mars so to the smaller data set). However, the majority of far (av. 0.98 wt. %). elemental concentrations are also typically lower or Portage is elevated in TiO2, P2O5 and Cr2O3, all of similar to those for Portage. Gusev (green) (at n=24, which show variation across the three soil categories. the largest sampling) exhibit the greatest compositonal 47th Lunar and Planetary Science Conference (2016) 2477.pdf

Cr2O3 abundances within Gusev and Meridiani Soils Ni, Zn and Br are among the most variable have a fairly consistent profile. However, values within elements at Bagnold Dunes, as quantified by APXS, the Gale Soils are typically higher than those for and appear to be depleted, relative to the other soil Meridiani or Gusev. TiO2 values for Gale and samples (Fig. 1). Whilst typical Bagnold Dunes Ni Meridiani Soils are generally higher than Gusev soils. values range from 490 to 511 ppm, WarsawBD has the Ni, Zn and Br show the highest degree of variation highest Ni (822 ppm) seen in any of the Martian soils. for each category. Ni and Zn values for Gale are higher Zr abundances are lower than those seen within the BD than those seen at Meridiani, which are lower than Gale soils - Barby 191 ppm is the lowest Zn value those from Gusev. Br abundances for the Gale soils are seen within Gale. Br values for the Bagnold Dunes samples are typically low (range 20-60 ppm); however, typically intermediate between those seen at Meridiani BD and Gusev soils. Br values show the most variation the Barby samples have higher Br abundance (103 ppm) than any other soil seen at Gale Crater. (Fig. 1) when ratioed to Portage (34 ppm), with highest 3.50 Gale Soils Ratio to Portage values seen at Gusev (range from 0 to 263 ppm). BarbyBD – crest 3.00 KibnasBD – trough WeissrandBD – disturbed WarsawBD - undisturbed Gale (n=10) Meridiani (n=6) Gusev (n=24) 2.50 Ave. 1σ Ave. 1σ Ave. 1σ

Oxide wt% 2.00 SiO2 43.15 0.47 46.15 0.95 46.16 0.78 TiO2 0.99 0.20 0.96 0.07 0.82 0.09 1.50 Al2O3 9.12 0.23 9.37 0.40 10.08 0.40

FeO 19.31 1.11 18.03 1.05 16.07 0.44 1.00 MnO 0.41 0.03 0.38 0.03 0.32 0.02

MgO 8.51 0.36 7.51 0.19 8.73 0.64 0.50 K2O 0.53 0.11 0.49 0.03 0.53 0.20

CaO 7.07 0.10 7.13 0.37 6.34 0.26 0.00 Na O MgO Al O SiO P O SO Cl K O CaO TiO Cr O MnO FeO Ni Zn Br Na2O 2.67 0.20 2.24 0.22 2.95 0.31 2 2 3 2 2 5 3 2 2 2 3 Cr2O3 0.45 0.07 0.40 0.06 0.38 0.12 Fig. 3: Comparison between Gale Soils and Bagnold P2O5 0.83 0.30 0.86 0.04 0.83 0.16 Dunes samples, ratioed to Portage. SO3 5.93 0.83 5.70 1.20 6.12 1.16 Cl 0.80 0.14 0.69 0.10 0.70 0.15 Ni (ppm) 531 76 415 66 527 168 Zn (ppm) 356 110 283 88 272 93 Conclusion: Gale soils (excl. Bagnold Dunes), Br (ppm) 39 20 29 4 46 52 and the basaltic soils at Gusev Crater and Meridiani Table 1. Averages for Gale (excl. Bagnold Dunes), Planum (Fig. 1, 2; Table 1) show consistency in Meridiani [1, 2] and Gusev [1, 2]. composition within limits, indicating a homogenous source and/or a homogenizing process (such as eolian Comparison to Bagnold Dunes: The first soil mixing). More significant differences in soil chemistry analysis from the Bagnold Dunes campaign was taken can be seen at Bagnold Dunes, both between the Gale on Sol 1182. Soil analyses from this ongoing campaign soils and those at Bagnold Dunes (Fig. 3) - the show considerable differences, both to previous Bagnold Dunes samples are more enriched in lighter analyses at Gale Crater and earlier MER analyses, and elements, (e.g., Si and Mg), but lower in K, P, and Ca, between individual Bagnold Dunes samples (Fig. 3). and depleted in volatiles (Ni, Zn and Br) – and Bagnold Dunes samples are higher in SiO2 than the between individual Bagnold Dunes soils. Gale soils, but typically lower than Gusev or As the Bagnold Dunes are an active dune system, Meridiani; however, BarbyBD has the second highest this variability may be related to position and BD SiO2 (48.11 wt. %) seen thus far in Martian soils. associated sorting, e.g., Barby , which is on the crest Although Al2O3 abundances are tightly constrained for of a ripple, displays more extreme variation from the other categories, the Bagnold Dunes values range from norm (i.e., Portage) than does the corresponding trough some of the lowest values seen for Martian soils (e.g., sample, KibnasBD (Fig. 3). The variability may also WarsawBD 8.46 wt. %), to samples higher than those suggest a limited contribution from eroded local seen in the Gale Soils (e.g., BarbyBD 10.87 wt. %). bedrock. Further APXS investigation of the Bagnold MgO values for the Bagnold Dunes are amongst the Dunes will add not only to our understanding of soils highest seen for Martian soils e.g., KibnasBD (9.97 wt. on Mars, and local variations, but also allow us to %). CaO and FeO abundances are comparable to Gale compare this active dune system with less active soils, whilst TiO2 values are lower. dunes, as planned for later in the MSL campaign. The Bagnold Dunes samples are lower in K2O, SO3 Acknowledgements: MSL-APXS science team and Cl, than the lowest Gale soils. SO3 values are the funding is provided by the CSA and NASA lowest for any soil analysed to date (e.g., WeissrandBD References: [1] Yen 2005, Nature, 436, 49-54. [2] 3.19 wt. %), although not the lowest values seen at Yen, A. S. et al. (2006) JGR, 111, E12S11. [3] Gale . K2O and Cl are comparable to the lowest Gusev Hurowitz, J.A. & Fischer, W. W. (2014) Geochim. et and Meridiani values. Cosmochim. Acta, 127, 25-38.