RESEARCH ARTICLE Among the grains are gray and red lithic frag- ments, clear/translucent crystal fragments, and spheroids with glassy luster (Fig. 1C). Some grains Curiosity at Gale Crater, Mars: showed bright glints in the martian sunlight, suggesting specular reflections from mineral crys- Characterization and Analysis tal faces or cleavage surfaces [similar features were observed by the optical microscope on board the Mars Phoenix Lander (9)]. MAHLI images of the Rocknest Sand Shadow of a sieved portion of material deposited on the observation tray (3) showed a variety of particle 1 2 3 4 4 5 D. F. Blake, * R. V. Morris, G. Kocurek, S. M. Morrison, R. T. Downs, D. Bish, types from clear to colored to dark, angular to 2 6 7 8 9 10 11 D. W. Ming, K. S. Edgett, D. Rubin, † W. Goetz, M. B. Madsen, R. Sullivan, R. Gellert, spherical, and dull to glassy-lustered (Fig. 1D). 11 12 13 14 15 16 I. Campbell, A. H. Treiman, S. M. McLennan, A. S. Yen, J. Grotzinger, D. T. Vaniman, During the scooping process, fragments of the 17 2 2 18 19 19 S. J. Chipera, C. N. Achilles, E. B. Rampe, D. Sumner, P.-Y. Meslin, S. Maurice, armored surface were cohesive to the extent that 19 19 20 21 22 23 22 O. Forni, O. Gasnault, M. Fisk, M. Schmidt, P. Mahaffy, L. A. Leshin, D. Glavin, “rafts” of surface crust were laterally compressed 24 22 25 16 26 27 A. Steele, C. Freissinet, R. Navarro-González, R. A. Yingst, L. C. Kah, N. Bridges, and displaced forward, and fragments of the crust 28 1 29 14 15 1 K. W. Lewis, T. F. Bristow, J. D. Farmer, J. A. Crisp, E. M. Stolper, D. J. Des Marais, fell into the scoop hole as cohesive units (Fig. 1B). 30 P. Sarrazin, MSL Science Team‡ The surface crust was also fractured and broken into rafts during scuffing by rover wheels (a pro- The Rocknest aeolian deposit is similar to aeolian features analyzed by the Mars Exploration cessbywhichanexcavationismadeintothesub- Rovers (MERs) Spirit and Opportunity. The fraction of sand <150 micrometers in size contains surface of unconsolidated regolith by rotating a ~55% crystalline material consistent with a basaltic heritage and ~45% x-ray amorphous material. single rover wheel). Material beneath the crust The amorphous component of Rocknest is iron-rich and silicon-poor and is the host of the volatiles also had some cohesion, as shown by the over- (water, oxygen, sulfur dioxide, carbon dioxide, and chlorine) detected by the Sample Analysis at steep walls of the scoop scars (much greater than Mars instrument and of the fine-grained nanophase oxide component first described from the angle of repose and vertical in some cases). basaltic soils analyzed by MERs. The similarity between soils and aeolian materials analyzed at The sand shadow has a discernible internal on February 1, 2017 Gusev Crater, Meridiani Planum, and Gale Crater implies locally sourced, globally similar structure. On the headwall and flanks of each basaltic materials or globally and regionally sourced basaltic components deposited locally at scoop trench, a lighter-tone layer is apparent all three locations. ~1 cm beneath and parallel to the dune surface (Fig. 1B). The origin of the layering is not un- he Mars Science Laboratory (MSL) rover material making up the sand shadow. We use derstood, and three hypotheses are viable. First, Curiosity began exploring the surface of Alpha-Particle X-ray Spectrometer (APXS) and Mars on 6 August 2012 (universal time co- CheMin data to determine the amounts and chem- 1National Aeronautics and Space Administration (NASA) Ames T 2 ordinated); until 13 September 2012, it conducted istry of the crystalline and amorphous components Research Center, Moffett Field, CA 94035, USA. NASA Johnson Space Center, Houston, TX 77058, USA. 3Department of Geolog- an initial engineering checkout of its mobility sys- of the sand shadow and compare these results with ical Sciences, University of Texas, Austin, TX 78712, USA. 4Depart- tem, arm, and science instruments. Curiosity spent global soil measurements from the Mars Explora- ment of Geology, University of Arizona, Tucson, AZ 85721, sols 57 to 100 (1) at a location named Rocknest, tion Rovers (MERs) and to basaltic martian mete- USA. 5Department of Geological Sciences, Indiana University, Bloomington, IN 47405, USA. 6Malin Space Science Systems, http://science.sciencemag.org/ collecting and processing five scoops of loose, un- orites analyzed on Earth. 7 consolidated materials extracted from an aeolian SanDiego,CA92191,USA. U.S. Geological Survey, Santa Cruz, CA 95060, USA. 8Max-Planck-Institut für Sonnensystemforschung, sand shadow (2). Results 37191 Katlenburg-Lindau, Germany. 9Niels Bohr Institute, Five scoops of material from the Rocknest University of Copenhagen, 2100 Copenhagen, Denmark. 10Center sand shadow were individually collected and Description and Interpretation of the for Radiophysics and Space Research, Cornell University, Ithaca, NY m Rocknest Sand Shadow 14850, USA. 11University of Guelf, Guelph, Ontario, N1G2W1, sieved (<150 m) by the Sample Acquisition, 12 – Canada. Lunar and Planetary Institute, Houston, TX 77058, USA. Sample Processing and Handling Collection The Rocknest sand shadow (7) is an accumula- 13State University of New York–Stony Brook, Stony Brook, NY Downloaded from and Handling for In situ Martian Rock Analysis tion of wind-blown sediment deposited in the 11790, USA. 14Jet Propulsion Laboratory/California Institute of (SA/SPaH-CHIMRA) instrument (3). Scoops 1 and lower-velocity lee of an obstacle in the path of Technology, Pasadena, CA 91109, USA. 15California Institute of 16 2 were processed by CHIMRA and discarded the wind. The orientation of the sand shadow in- Technology, Pasadena, CA 91125, USA. Planetary Science Institute, Tucson, AZ 85719, USA. 17Chesapeake Energy, Oklahoma to reduce (by entrainment and dilution) any ter- dicates that the constructive winds were from the City, OK 73102, USA. 18University of California, Davis, CA 95616, restrial organic contamination that may have north. The surface is composed of dust-coated, USA. 19Institut de Recherche en Astrophysique et Planétologie remained after a thorough cleaning on Earth (4) predominantly rounded, very coarse (1- to 2-mm) (IRAP), UPS-OMP-CNRS, 31028 Toulouse, France. 20Oregon State 21 and to coat and passivate the interior surfaces of sand grains (Fig. 1A). Trenches created during University,Corvallis,OR97331,USA. Finnish Meteorological Institute, Fl-00101 Helsinki, Finland. 22NASA Goddard Space the collection device with Mars dust. Portions the scooping show that these larger grains form Flight Center, Greenbelt, MD 20771, USA. 23Rensselaer Poly- (40 to 50 mg) of scoops 3 and 4 were delivered anarmoredsurface~2to3mminthickness(Fig. technic Institute, Troy, NY 12180, USA. 24Geophysical Laboratory, to the Chemistry and Mineralogy (CheMin) in- 1B). Beneath the armored surface, the bedform Carnegie Institution of Washington, Washington, DC 20015, USA. “ ” 25University Nacional Autonóma de México, Ciudad Universitaria, strument (5)andthe observation tray, a7.5-cm- interior consists of finer-grained material whose 26 diameter flat Ti-metal surface used for imaging size distribution extends through the resolution 04510 México D.F. 04510, Mexico. Department of Earth and Planetary Sciences, University of Tennessee, Knoxville, TN 37996, and analyzing scooped and sieved material with limit of Mars Hand Lens Imager (MAHLI) im- USA. 27The Johns Hopkins University Applied Physics Labora- Curiosity’s arm and mast instruments. Portions of ages (~30 mm per pixel under the conditions of the tory, Laurel, MD 20723, USA. 28Princeton University, Princeton, scoop 5 were delivered to both CheMin and the observation) (8). Because of CHIMRA’s 150-mm NJ 08544, USA. 29Arizona State University, Phoenix, AZ 85004, 30 Sample Analysis at Mars (SAM) quadrupole mass sieve, the larger grains that armor the surface USA. SETI Institute, Mountain View, CA 94043, USA. spectrometer/gas chromatograph/tunable laser could not be analyzed by CheMin. *Corresponding author. E-mail: [email protected] †Present address: Department of Earth and Planetary Sciences, spectrometer suite of instruments (6). Coarse sand grains that fell from the crust University of California, Santa Cruz, CA 95064, USA. We describe the physical sedimentology of into the scoop-troughs lost their dust coating ‡MSL Science Team authors and affiliations are listed in the Rocknest and suggest possible sources for the and show diversity in color, luster, and shape. supplementary materials. www.sciencemag.org SCIENCE VOL 341 27 SEPTEMBER 2013 1239505-1 Curiosity at Gale Crater the layering may represent changes in bulk com- of a surface veneer of coarse grains and a finer- could represent a lag formed as winds deflated position or grain size that occurred during dep- grained interior (7, 14), and the martian bed- finer grains. However, the paucity of coarse grains osition. Second, the layering may be the result forms have been considered analogous features within the interior indicates that an unreasonable of changes in oxidation state or other chemical (13, 15). The spatial grain-size sorting within amount of deflation would have had to occur to properties that occurred after deposition, in which coarse-grained ripples is thought to arise because produce the veneer. Second, the coarse-grained case the conformable nature of the banding and of the short grain excursion length of the coarse veneer could represent the terminal growth phase the surface of the sand shadow reflect depth- grains traveling in creep and the much longer ex- of the bedform. Because the size of a sand shad- dependent postdepositional chemical processes. cursion length of finer saltating grains (16). With ow is fixed by the upwind obstacle size (17), Finally, the layering may represent zones richer ripple migration, coarse grains are recycled through once the terminal size is approached, the lower or poorer in light-toned dust, reflecting times of the bedform and become concentrated on the wind speeds that characterize the wake and allow lesser or greater sand accumulation relative to ripple surface, where impacts from saltating grains for deposition of finer sediment are replaced by the air-fall dust.