Ref: 9.47) If Mars' atmosphere is mostly carbon dioxide, why is not it as hot as Venus?Answer: Although it has a carbon dioxide atmosphere, Mars' atmosphere is very thin, much less dense than Venus' or even Earth's.Diff: 1Section Ref: 9.58 ) What is the primary effect the carbon dioxide in Venus' atmosphere has on the planet.Answer: The high concentration of carbon dioxide has caused a runaway gree