At www.space.com/21306-moon-craters-asteroid-impacts.html … a quarter of the Moon's impact craters may retain substantial remnants of the asteroids and meteors that made them. In other words, when scientists claim to be looking at moon rocks – are they? The composition of the Moon has been deduced from Moon rocks brought back by expeditions – manned and unmanned. The problem is some of those moon rocks come from impact craters and could well belong to asteroids and rocks winging their way around the solar system. The article is at Nature Geoscience, (May 28th, 2013) and may be an explanation for some unusual minerals such as spindels and olivines. These are common on some asteroids, it is thought. A surprising amount of material from space is thought to litter the surfaces of not just the Moon but the planets in general, including the Earth. There may also be a substantial amount of material with an origin on Earth that was blasted upwards by impacts and ended up on the surface of the Moon, over millions and billions of years.