B. L. Ehlmann , 1 , 2 , K. S. Edgett 3 , B. Sutter 4 , 5 , C. N. Achilles 6 , M. L. Litvak 7 , M. G. A. Lapotre 1 , R. Sullivan 8 , A. A. Fraeman 2 , R. E. Arvidson 9 , D. F. Blake 10 , N. T. Bridges 11 , 12 , P. G. Conrad 13 , A. Cousin 14 , R. T. Downs 6 , T. S. J. Gabriel 15 , R. Gellert 16 , V. E. Hamilton 17 , C. Hardgrove 15 , J. R. Johnson 11 , S. Kuhn 2 , P. R. Mahaffy 13 , S. Maurice 14 , 18 , M. McHenry 2 , P.‐Y. Meslin 14 , D. W. Ming 5 , M. E. Minitti 11 , J. M. Morookian 2 , R. V. Morris 5 , C. D. O'Connell‐Cooper 19 , P. C. Pinet 14 , 18 , S. K. Rowland 20 , S. Schröder 21 , 22 , K. L. Siebach 23 , N. T. Stein 1 , L. M. Thompson 18 , D. T. Vaniman 24 , A. R. Vasavada 2 , D. F. Wellington 14 , 15 , R. C. Wiens 25 , A. S. Yen 2
07 December 2017
The Mars Science Laboratory Curiosity rover performed coordinated measurements to examine the textures and compositions of aeolian sands in the active Bagnold dune field. The Bagnold sands are rounded to subrounded, very fine to medium sized (~45–500 μm) with ≥6 distinct grain colors. In contrast to sands examined by Curiosity in a dust‐covered, inactive bedform called Rocknest and soils at other landing sites, Bagnold sands are darker, less red, better sorted, have fewer silt‐sized or smaller grains, and show no evidence for cohesion. Nevertheless, Bagnold mineralogy and Rocknest mineralogy are similar with plagioclase, olivine, and pyroxenes in similar proportions comprising >90% of crystalline phases, along with a substantial amorphous component (35% ± 15%). Yet Bagnold and Rocknest bulk chemistry differ. Bagnold sands are Si enriched relative to other soils at Gale crater, and H 2O, S, and Cl are lower relative to all previously measured Martian soils and most Gale crater rocks. Mg, Ni, Fe, and Mn are enriched in the coarse‐sieved fraction of Bagnold sands, corroborated by visible/near‐infrared spectra that suggest enrichment of olivine. Collectively, patterns in major element chemistry and volatile release data indicate two distinctive volatile reservoirs in Martian soils: (1) amorphous components in the sand‐sized fraction (represented by Bagnold) that are Si‐enriched, hydroxylated alteration products and/or H 2O‐ or OH‐bearing impact or volcanic glasses and (2) amorphous components in the fine fraction (<40 μm; represented by Rocknest and other bright soils) that are Fe, S, and Cl enriched with low Si and adsorbed and structural H 2O.
Because of ongoing aeolian activity, the Bagnold dunes consist of well‐sorted sands and lack the finer grains typical of Martian soils
Dune sands are chemically distinct with elevated Si, Mg, and Ni and lower H 2O, S, and Cl relative to all previously measured Martian fines
Two distinct, water‐/OH‐bearing amorphous components are identified: Fe‐, S‐, and Cl‐rich material in dust and Si‐rich material in the sands