From New Scientist: Do gravity holes harbour planetary assassins?
Ignore the title of this article; it relates to a silly extra article. The bulk of this is about Lagrangian points, which are places in space where the gravitational field of the Earth (or any planet) cancels out the gravity of the Sun. These areas actually have zero gravity, as opposed to the microgravity we usually see. A pair of probes called STEREO that launched in 2006 to observe the sun will also be used to observe L4 and L5, the two most stable of Earth's Lagrangian points.
The author also discusses Lagrangian point in regards to the most popular theory of the Moon's origin. If a Mar-sized object collided with the Earth in the distant past to form the Moon, where did that object come from? Perhaps L4 or L5, where the object would have been able to grow to that size and then be nudged out of orbit by the gravity of another body in the solar system, like Venus.