Astronomy 450 -- Spring 2000 Study questions for exam 2

In the second section of the course we have been examining the planets in our Solar System, trying to assess whether life might be present there now or might once have been present in the past. The candidates have been Mars, Venus, the big moon of Saturn Titan, one of the big moons of Jupiter, Europa, and the the atmosphere of Jupiter itself. We also have examined the remarkable meteorite ALH84001, analysis of which led to the serious suggestion that it has evidence of ancient microbial life on Mars, and touched on the issues of making the science-fiction idea of "terraforming" Mars a reality.

1. Describe the major classes of space missions, and list them in order of complexity and distance. What are the limiting factors, other than money, in the design of a space mission?
2. Describe the Greenhouse Effect and how it works to raise the surface temperatures of planets.
3. Describe how and why planets lose gases from their atmosphere to interplanetary space. Explain what determines which gases are lost.
4. Describe the surface conditions and principal atmosphere constituent for Earth, Mars, Venus, Titan, and Europa.
5. Describe the evidence indicating that liquid water formerly flowed across the martian surface. Why do we believe that water is probably frozen in the ground on Mars? Why can't liquid water exist on the surface of Mars now?
6. Is Mars geologically active today? Why do we believe this?
7. Be able to explain why Mars seems to have fulfilled all our prerequisites for life at the time life on Earth is believed to have started.
8. Why did the Viking lander biology experiments initially yield positive results which were ultimately believed to be false?
9. The text describes several environments on Mars where the search for life might be more likely to be successful; be able to describe several of these. What unifying themes characterize these environments?
10. Where are Mars's planetary inventories of carbon dioxide and water now?
11. What is the evidence that ALH84001 and other "martian" meteorites did in fact originate on Mars? How did these meteorites get to Earth?
12. Describe and explain the four lines of evidence originally presented indicating that martian organisms formerly existed in ALH84001.
13. Explain why the carbonates in ALH84001 indicate that warm liquid water was present on Mars.
14. What changes have to be made to the surface conditions on Mars to make Mars livable for humans? Why is the addition of material to Mars's atmosphere generally believed to be the means to making these changes?
15. Why is the simple addition of carbon dioxide to Mars's atmosphere probably inadequate to "terraform" Mars?
16. Where are Venus's planetary inventories of water and carbon dioxide now?
17. Why does Venus have no water now, while Earth still has most of its water? If you use the term "cold trap", make sure to explain how it works.
18. How do we obtain detailed maps of a planet like Venus whose surface is completely and permanently covered with clouds?
19. Earth has plate tectonics; Venus and Mars do not. How do we judge this, since we do not have the capability to measure continental drift (even if it was present) on the other two planets?
20. How old is the surface of Venus? What processes have caused older surface features to be erased?
21. We believe that somewhat more than a billion years ago and earlier, Venus may well have had relatively Earthlike surface conditions; today it resembles some of the literary descriptions of Hell. Explain what we think happened to make for the transformation.
22. Explain what density is, and how the bulk (average) density of a planet lets us estimate its composition.
23. Although methane (CH4) is present in Titan's atmosphere, and its surface temperature is right for liquid methane to exist there, large-scale bodies of more or less pure liquid methane probably can't be present on Titan. Why not?
24. Despite the unlikelihood of liquid methane bodies on the surface of Titan (see the previous question), there are reasons to believe that there should be large bodies of liquid on Titan's surface. Describe what this liquid is, and why we believe it should be there.
25. What is the "lapse rate" in an atmosphere? How does the observed lapse rate on Titan rule out methane "rain" there?
26. What does Earth-based radar observations of Titan indicate about the possible presence of oceans there?
27. Describe the likelihood of finding liquid water on Titan.
28. Titan probably cannot harbor life now, but it is still a very interesting place for exobiology studies. Why?
29. What is "tidal heating"?
30. What is "synchronous rotation" and how does it come about?
31. Although geological activity is a promising sign for a planet when being considered as a site for life [and you should be able to explain why this is], Io's extreme volcanic activity precludes life there. Why?
32. Why do we believe that there is a layer of water or ice a couple of hundred kilometers thick on Europa?
33. Explain "heat balance" and why we believe that it is likely that there is a subsurface "ocean" of liquid water on (more properly, in) Europa.
34. In our limited state of knowledge, where is life most likely to exist on Europa, if it is present at all?
35. Describe the reasons why the atmosphere of Jupiter is interesting as a place for the possible origin of life. What difficulties exist for the idea of life on Jupiter?