The stony asteroid 433 Eros is shaped roughly like a sweet potato twenty miles (thirty-three kilometers) long and eight miles (thirteen kilometers) wide. NEAR-Shoemaker’s close-up pictures of Eros showed that it was far more than just a chunk of rock in space. Even though it is a small object, it has had an eventful geological history. A single significant collision with another body about one billion years ago created a single crater, and the ejected material that landed back on the asteroid comprises all of the rocks and dust on the surface of Eros. The collision also sent seismic shockwaves through the entire asteroid, probably changing the shape of Eros and affecting all of the other craters and surface material that were there at the time. Eros has about the same density as Earth’s crust—2.4 times that of water—and tumbles through space as it orbits the Sun, making a complete orbit every 643 days and one complete rotation every five hours, sixteen minutes.