The Moon: Features and Origins: Practice Problem Solutions

1. Large, dark, smooth plains. They are solidified lava flows of dark volcanic rock (basalt) that filled big impact basins, not real seas.

2. The Moon rotates once for each orbit around Earth (tidal locking), so the same side faces us.

3. About one-sixth.

4. The Moon has no air or running water and no weather to erode them, so only new impacts change the surface.

5. A Mars-sized body (Theia) struck the young Earth. The debris went into orbit around Earth and gathered into the Moon.

6. Any two of: Moon rocks and Earth have almost identical oxygen composition; the Moon has a small iron core and low density like Earth's outer layers; computer simulations can make a Moon like ours.

7. Twelve people, in NASA's Apollo program (1969-1972).