The choices below describe four hypothetical planets. Which one's surface would you expect to be most crowded with impact craters? (Assume the planets orbit a star just like the Sun and that they are all the same age as the planets in our solar system.)

Question

Quizplus · Accepted Answer

The smaller the planet, the less gravity it has to hold onto an atmosphere, and the more likely it is that incoming objects will hit the surface. Also, slower rotation rates mean that the same side of the planet will face incoming objects more often, resulting in more impact craters. Therefore, choice C (same size as the Moon, same distance from the Sun as Mars, and a rotation rate of once every 10 days) is the best choice for a planet with the most impact craters on its surface.

The Choices Below Describe Four Hypothetical Planets