The planet is too small to hold heat. The planet is heated on only one side. The planet reflects heat from its dark side. The planet lacks an atmosphere to hold heat.
I gave my students this multiple choice question: Mercury, the planet nearest to the Sun, has extreme surface temperatures, ranging from 465°C in sunlight to -180°C in darkness. Why is there such a large range of temperatures on Mercury?

Only one answer is correct among these 4 choices:
- The planet is too small to hold heat.
- The planet is heated on only one side.
- The planet reflects heat from its dark side.
- The planet lacks an atmosphere to hold heat.

Could you tell me which one is correct?

The planet lacks an atmosphere to hold heat.