Evolving Visions

On the Cover: The plucky Mars Global Surveyor's Mars Orbiter Camera (MOC) zoomed in to get a closer look at erosion processes exposing hundreds of layers of similar thickness, texture, and pattern in an impact crater 64 kilometers (40 miles) wide in western Arabia Terra. In this MOC image, dark, windblown sand enhances the appearance of the layers. These layers provide a record of repeated, episodic changes that took place sometime in the Martian past. Layers toward the center of the crater are nearly horizontal, but those closer to or draping over the crater walls are tilted toward the basin center. Such relationships suggest the sediments creating these layers were deposited from above -- perhaps settling out of the Martian atmosphere or else out of water that might have occupied the crater as a lake.