One of the great accomplishments of the Apollo missions was to bring home hundreds of kilograms of lunar rock. Suddenly, geologists had a lifetime’s worth of lunar samples captured from several different spots across the Moon. These rocks and dust have been under continuous analysis since the Apollo 11 astronauts came home over 50 years ago. Scientists have samples of the Sun’s solar wind, particles from a comet’s tail, a few grams from an asteroid, with more coming shortly. But there’s one world, the focus of so much scientific study, which has never had a sample returned: Mars.