"The Great Walls relative visibility or otherwise from orbit has inspired much recent debate," the agency said in a May 11 press release accompanying a satellite image purporting to show "a winding segment of the 7,240-kilometer-long Great Wall of China situated just northeast of Beijing."

The image turns out to have been of a river feeding into the Miyun Reservoir. "Further acquisitions of the region are being planned with other ESA instruments to investigate the subject further," ESA said in a May 19 statement. The agency thanked professors from California State University and the Fudan University of Shanghai for helping correct the error.