Abstract

A search for life on Earth at kilometer resolution, using several thousand photographs obtained by the Tiros and Nimbus meteorological satellites, has been undertaken. No sign of life can be discovered on the vast majority of these photographs. Due principally to the small contrast variations involved and the difficulty in reproducing observing conditions at satellite altitudes, no seasonal variations in the contrast of vegetation could be detected. Of several thousand Nimbus 1 photographs of essentially cloudfree terrains, one feature was found indicative of a technical civilization on Earth—a recently completed interstate highway—and another suggestive feature was discovered, possibly a jet contrail. A striking rectilinear feature was found on the Moroccan coast; however, it appears to be a natural peninsula. An orthogonal grid, discovered in a Tiros 2 photograph, is due to the activities of Canadian loggers, and is a clear sign of life. It appears that several thousand photographs, each with a resolution of a few tenths of a kilometer, are required before any sign of intelligent life can be found with reasonable reliability. An equivalent Mariner 4 system—taking 22 photographs of the Earth with a resolution of several kilometers—would not detect any sign of life on Earth, intelligent or otherwise.