Star: average rate of star formation in our galaxy. Star with two planets: fraction of those stars that have planets. Three planets: average number of planets that can potentially support life per star that has planets. Cell: fraction of planets that could support life that develop life at some point. Gear: fraction of planets with life that develop intelligent life. Radio signal: fraction of civilizations that develop a technology that send detectable signs of their existence into space. Clock: length of time civilizations broadcast detectable signals into space.
德雷克方程
Collection、remix+17890、remix+169903、remix+230920、remix+242496、Set of icons that pictorially represent factors of the Drake Equation.
採集、混音+ 17890、混音+ 169903、混音+ 230920、混音+ 242496、圖標表示德雷克方程的因素的圖標集。
資料來源：openclipart ( https://openclipart.org/ )