Many Minimoons Of Earth

A new study using one of the longest, most complex computer simulations yet done suggests Earth often has more than one moon.

The study says that over the billions of years of Earth history, the planet's gravitational well-- the deepest in the inner Solar System, after all-- has captured many small asteroids and held them in orbit for months, years, or decades. Those orbits, however, have been highly elliptical, and the interplay of the interacting gravitational fields of Earth, the Moon, and the Sun eventually kick the minimoons out of Earth orbit and back into solar orbit.

Had such a minimoon been around the past few decades, it would have been a real boon for science, and obviously an early target in the Space Age. The possibility does suggest an interesting approach for the future. Instead of waiting for Earth to capture another one on its own, we could help things along by maneuvering a small body into such a temporary Earth orbit. That would extend our capabilities in space while giving us an asteroid to study at close range using the full resources of Earth's astronomical community. By setting up sophisticated science packages on the asteroid while it orbits Earth and waiting, we could eventually have a very good observatory in solar orbit.