Among the solar system's oldest inhabitants, comets and asteroids formed within a swirling cloud of gas and dust in the area of space that eventually hosted the sun and its planets. Here Natalie Starkey tells the story of these enigmatic celestial objects, revealing how scientists are using probes like Rosetta and Stardust to help understand a crucial time in astronomical history. Exploring comets and asteroids may allow us to shape the story of Earth's future, Starkey suggests, enabling us to protect our planet from the threat of a catastrophic impact from space, and maybe to even find signs of life or recover valuable raw materials from them.