2. Crater The depression at the summit of a volcano or that which is produced by a meteorite impact.
3. Ray Any of a system of bright elongated streaks, sometimes associated with a crater on the moon.
4. Mare The Latin name for smooth areas of the moon formerly thought to be seas.
5. Rille Long channel associated with lunar maria; a rille looks similar to a trench or a valley.
6. Lunar Regolith A thin, gray Layer on the surface of the moon, consisting of loosely compacted, fragmented material believed to have been formed by repeated impacts of meteorites.
7. Key Concept Most craters were produced by the impact of rapidly moving debris.
8. Key Concept Maria, ancient beds of basaltic lava, originated when asteroids punctured the lunar surface, letting magma bleed out.
9. Key Concept The most widely accepted model for the origin of the moon is that when the solar system was forming, body the size of mars impacted Earth.
