S PIRIT AT G USEV C RATER 14. R. L. Folk, Petrology of Sedimentary Rocks, Hemphill 23. W. K. Hartmann, J. Anguita, M. A. de la Casa, D. C. 32. M. P. Golombek, N. T. Bridges, J. Geophys. Res. 105, Publishing (Austin, TX, 1980). Berman, E. V. Ryan, Icarus 149, 37 (2001). 1841 (2000). 15. R. Greeley et al., Science 305, 810 (2004). 24. W. K. Hartmann et al., Nature 397, 586 (1999). 33. Research was supported by NASA through the Mars ECTION 16. H. Y. McSween et al., Science 305, 842 (2004). 25. F. Horz, M. J. Cintala, W. C. Rochelle, B. Kirk, Science Exploration Rover Project. Our sincere thanks go to S 17. M. P. Golombek et al., Lunar Planet. Sci. [CD-ROM], 285, 2105(1999). the Mars Exploration Rover management, staff, and abstract 2185(2004). 26. J. A. Grant, P. H. Schultz, J. Geophys. Res. 98, 15033 engineering teams for their outstanding support and 18. K. E. Herkenhoff et al., Science 305, 824 (2004). (1993). operation of Spirit. 19. H. J. Melosh, Impact Cratering, Oxford Univ. Press 27. P. R. Christensen et al., Science 305, 837 (2004). (New York, 1989). 28. S. W. Squyres et al., Science 305, 794 (2004). Plates Referenced in Article PECIAL 20. J. A. Grant, P. H. Shultz, J. Geophys. Res. 98, 11025 29. R. P. Irwin, A. D. Howard, T. A. Maxwell, Lunar Planet. www.sciencemag.org/cgi/content/full/305/5685/807/ S (1993). Sci. [CD-ROM], abstract 1852 (2004). DC1 21. M. Hurst, M. P. Golombek, R. Kirk, Lunar Planet. Sci. 30. G. Komatsu, V. R. Baker, J. Geophys. Res. 102, 4151 Plates 1, 3, 5, and 9 [CD-ROM], abstract 2068 (2004). (1997). 22. R. E. Arvidson et al., Science 305, 821 (2004). 31. K. A. Milam et al., J. Geophys. Res. 108, 8078 (2003). 3 May 2004; accepted 28 June 2004 REPORT Wind-Related Processes Detected by the Spirit Rover at Gusev Crater, Mars R. Greeley,1 S. W. Squyres,2 R. E. Arvidson,3 P. Bartlett,4 J. F. Bell III,2 D. Blaney,5 N. A. Cabrol,6 J. Farmer,1 B. Farrand,7 M. P. Golombek,5 S. P. Gorevan,4 J. A. Grant,8 A. F. C. Haldemann,5 K. E. Herkenhoff,9 J. Johnson,9 G. Landis,5 M. B. Madsen,10 S. M. McLennan,11 J. Moersch,12 J. W. Rice Jr.,1 L. Richter,13 S. Ruff,1 R. J. Sullivan,2 S. D. Thompson,1 A. Wang,3 C. M. Weitz,14 P. Whelley,1 Athena Science Team Wind-abraded rocks, ripples, drifts, and other deposits of windblown sediments are Aprons of granular debris occur as isolat- seen at the Columbia Memorial Station where the Spirit rover landed. Orientations ed patches on the regolith and around some of these features suggest formative winds from the north-northwest, consistent with rocks. For example, the rock Adirondack (2) predictions from atmospheric models of afternoon winds in Gusev Crater. Cuttings has an encircling debris apron that extends 5 from the rover Rock Abrasion Tool are asymmetrically distributed toward the to 20 cm from the edge of the rock. The south-southeast, suggesting active winds from the north-northwest at the time aprons consist of coarse grains that have (midday) of the abrasion operations. Characteristics of some rocks, such as a spectral properties similar to those of Adiron- two-toned appearance, suggest that they were possibly buried and exhumed on the dack and the other basaltic rocks in the area order of 5 to 60 centimeters by wind deflation, depending on location. (11, 19). Therefore, some of the more angular coarse-grained material is probably derived In the current environment of Mars, wind ap- edges, and features generated by the rover pears to be the most frequent agent of surface during operations that suggest active winds. 1 modification, resulting in albedo patterns that The surface at Columbia Memorial Station Department of Geological Sciences, Arizona State University, Box 871404, Tempe, AZ 85287–1404, change on time scales as short as a few weeks consists of rocks, regolith, dark granules, and USA. 2Department of Astronomy, Cornell University, (1). Abundant dune forms, mantles of wind- fine-grained material, including dust (8, 9). 428 Space Sciences Building, Ithaca, NY 15853–1301, blown deposits, and wind-eroded features are Patches of red regolith range in size from 0.5 m USA. 3Department of Earth and Planetary Sciences, seen from orbit in many parts of Mars, includ- across to as large as 15 m across. Bonneville Washington University, One Brookings Drive, St. Lou- is, MO 63031–4899, USA. 4Honeybee Robotics, 204 ing the three previous sites where successful (10) crater and many of the small depressions, Elizabeth Street, New York, NY 10012, USA. 5Jet landings have occurred. Understanding the pro- called hollows, are partly filled with regolith Propulsion Laboratory, 4800 Oak Grove Drive, Pasa- cesses that form aeolian (wind-related) features deposits. Light-toned material was inferred to dena, CA 91109–8099, USA. 6Ames Research Center, 7 provides insight into the evolution of the mar- be dust, the upper surfaces of some rocks, the Moffett Field, CA 94035–1000, USA. Space Science Institute, University of Colorado, Boulder, CO 80301, tian surface, including rates of erosion and dep- rover solar panels, and the Panoramic Camera USA. 8Center for Earth and Planetary Studies, Nation- osition. The Mars Exploration Rover (MER) (Pancam) calibration target (11). Although dust al Air and Space Museum, Smithsonian Institution, Spirit landed near the middle of Gusev Crater grains are too small to be resolved by the Washington, DC 20560–0315, USA. 9U.S. Geological (2–5) in a relatively low-albedo zone (6) Microscopic Imager (MI) (12), previous esti- Survey, 2255 North Gemini Drive, Flagstaff, AZ 86001–1698, USA.10Niels Bohr Institute for Astrono- considered to be a track left by the passage of mates suggest that martian dust is a few mi- my, Physics, and Geophysics, Center for Planetary dust devils that removed bright dust to expose crometers in diameter (13, 14). Science and Ørsted Laboratory, University of Copen- a relatively darker substrate (Fig. 1A). Com- An MI image of a regolith patch shows a hagen, Universitetsparken 5, DK-2100 Copenhagen, parison of orbital images taken of the same bimodal size distribution of particles (Fig. Denmark. 11Department of Geosciences, State Uni- area from July 2003 to January 2004 show 1B) that includes coarse (1 to 3 mm) grains versity of New York at Stony Brook, Stony Brook, NY 11794–2100, USA. 12Department of Earth and Plan- changes in the tracks, indicating that dust and finer grains smaller than a few hundred etary Sciences, University of Tennessee, 1412 Circle devils were recently active. micrometers in diameter. Although some Drive, Room 306, Knoxville, TN 37996, USA. 13Deut- Here, we describe initial analyses of aeo- coarse grains are subangular, most are round- ches Zentrum fu¨r Luft-und Raumfart (German Aero- lian features during the first ϳ90 sols (7)of ed, suggesting erosion during transport. We space Center)–Institute of Space Simulation, Linder Hoene, D-51170 Cologne, Germany. 14National Aero- operation. Wind-related features include sed- propose that the dark coarse particles are nautics and Space Administration (NASA) Headquar- iments (some of which are organized into lithic fragments on the basis of their basaltic ters, Washington, DC 20546–0001, USA. bedforms such as ripples), wind-abraded fea- composition (16, 17) and appearance in the *To whom correspondence should be addressed. E- tures on rocks, eroded zones around rock MI images (18). mail: [email protected] 810 6 AUGUST 2004 VOL 305SCIENCE www.sciencemag.org S PIRIT AT G USEV C RATER S PECIAL from physical weathering of rocks in the area, with the larger bedforms having longer wave- with the visible-wavelength albedos. The high- as suggested for the Mars Pathfinder (MPF) lengths. The larger bedforms are only seen er albedo southeast slopes show a thermal in- site on the basis of spectral properties (14). within Bonneville crater and on the outer flanks frared (IR) signature of dust that is equivalent to Although the dark regolith within Bonneville of the crater and can be identified in orbital the globally homogeneous dust (20). Spectra of S crater was not examined in situ, the regolith images. In cross section, most bedforms are the lower-albedo northwest-facing slopes sug- ECTION has similar aprons on its surface. slightly asymmetric, with the southeast sides gest the presence of materials compositionally Bedforms are common at the site and range being steeper and higher in albedo than the similar to the rocks seen at the site and is in size from 0.1 m long by 0.03 m wide by northwest sides. Thermal infrared spectral attributed to thepresence of particles similar to 0.02 m high to 10 m long by 2 m wide by 0.5 m emissivity measurements (16) across meter- those composing the debris aprons. high. They have wavelengths of 0.06 to 10 m, scale bedforms show asymmetry that correlates MI images taken on one bedform named Fig. 1. (A) Mars Orbiter Camera (MOC) image R12- 01091. View of the Spirit site from orbit showing the Columbia Memorial Station (star) and the impact crater, Bonneville. The relative dark zones are tracks left by the passage of dust devils. One prominent track crosses Bonneville crater. (B)MI image, 2M130463156EFF0- 900P2943M21, of regolith showing large, subangular granules set in smaller, sand- size grains. The spectral properties of the granules suggest that they are lithic fragments. (C) Pancam im- age, 2P129911125FFL0500- P2399L2M1, of the ripple, Arena. (D) MI image, 2M1- 30001357EFF0506P2953M- 2M1, of Arena crest, showing well-sorted rounded grains.