Our changing view of Mars

Mars has always captivated us. Its fiery color and erratic apparent motion got the attention of sky watchers across the ancient world. Nineteenth-century astronomers interpreted its complex surface markings as evidence for river channels or, more imaginatively, an engineered network of canals. Changes in Mars's appearance throughout its annual cycle-later understood to be caused by seasonal ice and dust-prompted talk of an active biosphere until the dawn of the space age.