To See a World in a Grain of Sand

In the 1960s and 1970s, NASA's Apollo and the Soviet Union's Luna missions captured imaginations across the world and revolutionized our understanding of Earth's moon and the Solar System. Over 50 years on, the realm of space exploration has expanded significantly, both in terms of the celestial bodies that have been explored and the nations working on these endeavors. In the coming decades, we will return samples from Mars and one of its moons, and humans will return to the Moon. This article sets the scene for this Elements issue, which will explore what we have learned about the formation and evolution of planetary bodies, including Earth, from analysis of returned samples, the links with orbital datasets, and priorities for the future.