Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. A near-Earth object (NEO) is a Solar System object whose orbit brings it into proximity with the Earth. All NEOs have a closest approach to the Sun of less than 1.3 AU. They include a few thousand near-Earth asteroids (NEAs), near-Earth comets, a number of solar-orbiting spacecraft, and meteoroids large enough to be tracked in space before striking the Earth. It is now widely accepted that collisions in the past have had a significant role in shaping the geological and biological history of the planet. NEOs have become of increased interest since the 1980s because of increased awareness of the potential danger some of the asteroids or comets pose to the Earth, and active mitigations are being researched. Learn more about near-Earth objects, the dangers they pose and the research done on them in this book.