since travel to other planets was not possible at that time, some people suggested ways to signal the extraterrestrials even before radio was discovered. carl friedrich gauss is often credited with an 1820 proposal that a giant triangle and three squares, the pythagoras, could be drawn on the siberian tundra. the outlines of the shapes would have been ten-mile-wide strips of pine forest, the interiors could be rye or wheat. joseph johann littrow proposed in 1819 to use the sahara as a sort of blackboard. giant trenches several hundred yards wide could delineate twenty-mile-wide shapes. then the trenches would be filled with water, and then enough kerosene could be poured on top of the water to burn for six hours. using this method, a different signal could be sent every night.