Go to: INCA CITY A series of rectilinear ridges near the south pole of Mars comes into sharp focus in a new image from the Mars Global Surveyor. Dubbed the "Inca City," the strange formations could be modern sand dunes or ancient ones, buried, hardened and later exposed by erosion, according to planetary scientists. The wide-angle photograph shows that the ridges are part of a larger circular structure about 86 km (53 mi) across, possibly the remnant of an ancient, eroded impact crater. (08/28/02)