The Moon was imaged with the OSIRIS Narrow Angle Camera (NAC) at 07:36 CET, about nine hours after (ESAS) Rosetta's closest approach to Earth. See other pictures of the Moon and the Earth, and read about Rosetta at the European Space Agency web site.
Read about the origin of the Moon at this page of the NASA RedShift Astronomy web site. "New observations from NASA's Spitzer Space Telescope suggest that moons like Earth's - that formed out of tremendous collisions - are uncommon in the universe, arising at most in only 5 to 10 percent of planetary systems."
On this page there is also a link to an animation of "a massive collision between rocky, embryonic planets as big as mountain ranges. Such collisions form the basis of the planet-building process."
In another story, on the Sky and Telescope web site, you can read about a Chinese spacecraft named Chang’e 1 which will study the Moon at close range after successfully settling into lunar orbit on November 5.