Images of craters and measurements of a thin atmosphere—much thinner than expected—indicating a relatively inactive planet exposed to the harshness of space, generally dissipated hopes of finding intelligent life on Mars. Life on Mars had been the subject of speculation and science fiction for centuries. If there was life on Mars, after Mariner 4 most concluded it would probably be smaller, simpler forms. Others concluded that a search for life on Earth at kilometer resolution, using several thousand photographs, did not reveal a sign of life on the vast majority of these photographs; thus, based on the 22 photographs taken by Mariner 4, one could not conclude there was no intelligent life on Mars.