NEAR scientists have found that most of the bigger rocks scattered across Eros were blown from a single crater in a meteorite collision approximately 1 billion years ago. This impact may also be the reason why nearly half of the Erotian surface doesn't have small craters. It was first thought that the debris thrown up by the collision filled in the smaller craters (those less than half a kilometer across). A study of crater on the surface shows that the areas with the fewest craters are within 9 kilometers of the impact point. This includes the opposite side of the asteroid but still within 9 kilometers.