A number of space probes have sent back hundreds of close-up images of these objects. Here is an image that places these objects side by side along with some comets, to give you an idea of their relative sizes. This one shows why Vesta stands out as being essentially different than most other asteroids. Eros is one that periodically makes a close approach to Earth. Japan has even landed on Itokawa. I have put the Eiffel Tower on Itokawa to give you an idea of how small this asteroid is. Here’s minor planet Gaspra, resting on metropolitan Detroit! Many have been found to have moons, such as Ida. The Dawn spacecraft has been in orbit around Vesta, taking detailed images such as this one. Here’s the greatest hits of the Dawn mission. We have learned that some asteroids such as Ida are binary, having a small moon orbiting the main body. With over a half million minor planets discovered, we now identify different families of these objects. The Apollos, Atens and the Amors are of special interest, since they make close approaches to Earth. The Trojan asteroids are bound by Jupiter’s gravity to lead and follow that planet. Some of these objects come uncomfortably close to Earth. Is anyone checking to see if our planet is in immediate danger of an impact?