(3 pts.) (a) Give a definition and an example of a greenhouse gas.
(5 pts.) (b) Explain how greenhouse gasses act like one-way valves. What exactly is allowed to flow in, and what exactly is prevented from leaving? (Please be specific. Terms like “energy,” “heat,” and “radiation” are not specific enough.)
(4 pts.) (c) In another solar system, we discover two terrestrial planets, one which has a surface temperature twice as hot as the other. Neither planet has significant volcanic activity. Propose four hypotheses which might explain the difference in surface temperature, and explain precisely how each hypothesis would account for the difference.
(2) Cool Venus
In Unit 6.1 we showed that in the absence of any greenhouse effect, the equilibrium temperature of Venus would be lower than the equilibrium temperature of the Earth, even though Venus is closer to the Sun.
(4 pts.) (a) Explain this unexpected result in a sentence or two.
(2 pts.) (b) Now, suppose that Venus has neither clouds nor greenhouse gases. What would happen to the temperature of Venus? Would it be hotter or cooler than it is now? Why?
(2 pts.) (c) How are clouds and volcanoes linked on Venus? What change in volcanism might result in the disappearance of clouds? Explain.
(3) Mars Climate Evolution
(4 pts.) (a) What is the evidence that Mars’ atmospheric pressure and temperature were once much greater than they are today?
(4 pts.) (b) Where did all the atmospheric gas go? Where is this gas today? Give at least two different places where substantial amounts of this gas went.
(2 pts.) (c) Is it likely that Mars will have a thicker and warmer atmosphere in the future (assuming humans do not interfere)? Explain why or why not.
(3 pts.) (d) Today there are no active volcanoes still erupting on Mars. But what if there were? What if Mars had maintained the same level of volcanic activity that the Earth and Venus have. How would this have changed the development of Mars’ atmosphere? What would you expect it to be like on Mars today?
(4) Earth & Venus Climate Evolution
(4 pts.) Explain how the atmospheric histories of Venus and the Earth caused conditions on the surfaces of the two planets to become so different. In particular, what happened to the water on Venus and to the carbon dioxide on Earth?
(5) UFOs and Aliens
(3 pts.) Most astronomers are optimistic that we may soon discover life on other planets, and someday perhaps even intelligent life. However, most astronomers are extremely skeptical about reports that UFOs are spacecraft piloted by intelligent beings from other solar systems. Why are they so skeptical? Please write up a detailed and thorough response to this question, explaining all of the relevant issues.