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Names have been assigned to geographic features by the MER team for planning and operations purposes. The names are not formally recognized by the International Astronomical Union.

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R. Rieder et al., Science306, 1746 (2004). Note the abundance of salt-forming elements in soils.

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The ability to resolve individual grains with the MI depends on the illumination of the scene and the contrast between the grain and its surroundings. Typically, an object must subtend at least 3 pixels to be recognized in an image (about 100 μm for the MI).

Grain-size classifications use the Wentworth scale (25).

An example of a terrestrial eolian lag is shown in figure 6 of Greeley et al. (26).

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The U.S. Geological Survey MER Team developed MI software and created various data products, including some of those displayed in this issue: B. Archinal, J. Barrett, K. Becker, T. Becker, D. Burr, D. Cook, D. Galuszka, T. Hare, A. Howington-Kraus, R. Kirk, E. Lee, B. Redding, M. Rosiek, D. Soltesz, B. Sucharski, T. Sucharski, and J. Torson (project engineer). The Ames MER team and M. Lemmon developed software to merge focal sections and generate anaglyphs from them. The MER Rover Planners provided excellent support of the MI investigation by commanding the instrument arm and MI dust cover. Reviews of this manuscript by J. Bishop, M. Chapman, J. Kargel, and an anonymous referee are much appreciated. This research was carried out for the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration.