On the Cover: This enhanced false color mosaic of <i>Landsat</i> images covers a portion of the eastern Sahara. The Uweinat Mountain, 40 kilometers across, is the largest topographic prominence, and causes a vast spindle-shaped, sand-free zone. The mountain rises at the borders of Egypt, Libya and Sudan. Smaller features also cause a dark, sand-free zone in their lee. Similar features have been imaged by spacecraft orbiting Mars.
8 Alien Life—Forms and Function in Fluids: James Burke looks at life on Earth to think about life on other planets.
10 Is It Earth...or Is It Mars? Farouk El-Baz compares the planets with satellite images.
7 Q&A What is the speed necessary for Galileo to reach Jupiter?
12 News & Reviews Soviets in space; where does NASA go from here?
13 World Watch The shuttle program after Challenger; Mars Observer and CRAF.
14 Society Notes New additions to the Society.