Question

Which of the following best explains why Mars' and Venus' surface temperatures vary, despite both planets having atmospheres that contain mostly carbon dioxide?
A. Mars has a surface of red rocks and sand which reflect heat.
B. Venus has a surface of high mountains which absorb heat.
C. Mars has a thin atmosphere that cannot hold much heat.
D. Venus has a thick atmosphere which blocks heat from the surface.

Answer 1

C. Mars has a thin atmosphere that cannot hold much heat.

Mars' atmosphere is very low pressure and sparse, so its greenhouse effect is weak and heat quickly escapes. Venus' atmosphere is extremely dense, producing a very strong greenhouse effect that traps heat and makes the surface much hotter.