Mars — the Red Planet, the god of war, the home of life? Of all the planets in the solar system, Mars ranks first on a short list as a home for life beyond Earth, past or present, in the minds of scientists and science fiction writers alike. Today, we are a bit closer to a definitive answer than we were when ancient people looked up at the ruddy “star” glimmering in the evening sky and called it Mars. The study of Mars led early astronomers to understand how the solar system works, and to develop a model that displaced Earth — and humans — from the center of the universe. They made one small step toward our current understanding of the universe.