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The article presents an image of China's Badain Jaran desert, which covers more than 40,000 square kilometers. The desert is home to some of the world's tallest stationary dunes, seen here from the International Space Station. They can stand 500 meters tall and cast immense shadows. What keeps these piles of sand immobile despite arid, windy conditions is a previously unknown source of groundwater, says Ling Li, an environmental engineer at the University of Queensland in St. Lucia, Australia. Analyses of the water suggest that it's snowmelt that flows hundreds of kilometers through fractured rocks to reach the desert. The annual flow, estimated to be 0.5 cubic kilometer, could provide an alternative to a planned $500 million river-diversion project, Li and his colleagues say.

Reports that images from a trio of radars on the space shuttle show not only the existing Great Wall of China, but also a previous edition running parallel to it. The ability of the triple-radar instrument, known as SIR-C/X-SAR, to reveal hidden structures and help map man-made features.

Looks at how scientists are using a radar system carried aboard the space shuttle to find lost pieces of China's Great Wall. Brief history of the Wall; Condition of Wall; How the Wall's reflection of radar shows up clearly in images captured by the SIR-C/XSAR radar system; Radar system as a joint project of the United States, German, and Italian space agencies; Other uses of space radar.