PTYS/ASTR 206 (Sec. 2) Spring 2007 Mid-Term Exam #2: 3/29/07 (Page 1/7) NAME: KEY (C)

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1 PTYS/ASTR 206 (Sec. 2) Spring 2007 Mid-Term Exam #2: 3/29/07 (Page 1/7) NAME: KEY (C) Part 1: Short Answer (please fill out the answers in the space provided; do not mark the scantron sheet!). Short-answer questions are worth 5 pts each. Your answers should be fairly brief and to the point, but also contain enough information to be complete. Please do not give very long narratives this is not an essay! A diagram may be used to clarify your answer. 1. What are three pieces of evidence for water on Mars (either flowing on the surface in the distant past, or as it exists presently). Any three of the following: 1. Closeup images of Mars reveals the compelling visual evidence of dried up river beds 2. Similarly, other show visual evidence of dried-up vast flood plains. 3. Other images show gullies in the walls of craters 4. More direct evidence comes from the fact that the Northern and Southern polar caps have been seen to recede as CO2 sublimtes into the atmosphere, but then stops receding. What remains is water ice, which does not sublimate into the atmosphere at those temperatures 5. Direct evidence came from gamma-ray spectroscopy seen by the GRS instrument on Mars Global Surveyor. 2. What causes aurorae and why is it more likely to observe them at very high northerly (Aurora Borealis) or southerly (Aurora Australis) latitudes compared to lower latitudes, such as Tucson where they are very rare? (Note that there are two parts to this question!) Aurorae are emissions produced by atoms in the upper atmosphere that are excited by high-energy charged particles coming from the magnetosphere. Because the lines of magnetic force run North-South (like the iron filings in a bar magnet), they lead these particles into Earth s poles. Therefore, aurorae are most commonly seen in at high northerly and southerly latitudes, although, occasionally, if the magnetosphere is compressed sufficiently, they can be seen as far south as Tucson. 3. How do we know that sunspots are regions of cooler gas in the solar atmosphere? Sunspots are dark, and, hence, because of the Stefan-Boltzmann law (which states that the total emitted flux or brightness depends on the temperature as F=σT 4 ), the gas there must be cooler. Please write below this line only if absolutely necessary (Over for two more questions)

2 PTYS/ASTR 206 (Sec. 2) Spring 2007 Mid-Term Exam #2: 3/29/07 (Page 2/7) 4. Briefly, how did the Moon form, according to a popular theory? Name two aspects of the Moon s known composition that this theory explains. The Moon is thought to have formed when a large Mars-sized object collided with Earth shortly after Earth formed, and was differentiated. This collision tore off a large piece of Earth that eventually collected under its own gravity to form the Moon. This theory explains why the Moon is (a) composed mostly of material that is similar to the mantle of the Earth, but (b) has very little iron. 5. Describe the greenhouse effect in a planetary atmosphere. Include in your description the names (or molecular symbols) of two (not more) greenhouse gasses and what they do. The greenhouse effect occurs when a planet s atmosphere contains certain gasses that make the atmosphere act as a thermal blanket. Incident solar radiation, accounting for most of the heating of Earth s surface peaks in the visible part of the spectrum. Radiation emitted by Earth s surface peaks in the infrared part of the spectrum which is absorbed by greenhouse gasses (such as CO 2 and H 2 0) in the atmosphere and cannot escape directly. Because of the absorption of Earth s emitted energy by these gasses, the resulting atmospheric temperature equilibrium occurs at a higher temperature than if these gasses were not present in the atmosphere. Please write below this line only if absolutely necessary

3 PTYS/ASTR 206 (Sec. 2) Spring 2007 Mid-Term Exam #2: 3/29/07 (Page 3/7) Part 2: Multiple Choice Mark the appropriate answer in the appropriate place (i.e. in numbers 1-32) on the scantron sheet. Use a number 2 pencil. Be sure to write your name and fill in the ovals, in the upper left. Multiple-choice questions are worth 2-½ pts each. Two extra-credit questions are the end. 1. On Mars, which of the following have NOT been seen or detected? A) dust storms and dust devils B) thin, wispy clouds C) water ice D) active volcanoes 2. Why are there very few impact craters on the surface of Venus compared to the surfaces of Mercury and Mars? A) ancient oceans washed away all the craters formed during the early bombardment phase. B) immense lava flows have covered up all but the younger craters. C) Venus s surface does not get impacted as often as these other worlds because of its thick atmosphere which burns up nearly all asteroids coming through it D) wind erosion from its dense atmosphere and chemical action from its corrosive clouds have destroyed most craters. 3. Which solar-system body below has never had a spacecraft from Earth land on its surface? A) The Moon B) Venus C) Mercury D) Mars 4. What is the most important factor in determining how active a planet or moon s interior is likely to be, and how long it is likely to stay active? A) The object s distance from the Sun. B) The object s size C) The object s composition. D) the amount of radioactive material in the vicinity 5. The deepest diamond mines go over a km into the Earth. It is found to be very hot there. What is primary source of this heat? A) Radioactive decay of elements within Earth s interior, and residual heat after formation B) Absorption of solar energy C) Tidal forces from the Moon D) Electrically conducting currents within Earth s interior 6. What are the polar caps on Mars primarily composed of? A) only water ice B) a mixture of methane, ammonia, and water ices, whose relative abundances vary with the seasons. C) only carbon-doxide ice D) carbon-dioxide ice overlying thicker water ice. 7. What is thought to cause the drifting of Earth s continents on plates? A) Earthquakes B) Precession of the Earth s spin axis C) Tidal forces from the Moon and Sun acting on the continental plates D) Large-scale circulation of partly molten or plastic rock in Earth's interior

4 PTYS/ASTR 206 (Sec. 2) Spring 2007 Mid-Term Exam #2: 3/29/07 (Page 4/7) 8. Which of the following best describes the rotation of Venus on its axis? A) Rapid and retrograde (backward, or opposite to its motion around the Sun) B) Rapid and prograde (forward, or in the same direction as its motion around the Sun) C) Slow and retrograde D) Slow and prograde 9. What is HiRISE? A) A telescope onboard Mars Reconnaissance Orbiter imaging the planet at unprecedented resolution B) A future mission to land on Mars and analyze samples in its polar regions C) A proof-of-concept mission that landed on Mars in 1997 and took several images of the planet and also had a small rover that analyzed the soil D) The spectrometer onboard the spacecraft Mars Global Surveyor that confirmed the existence of remnant magnetic fields on Mars 10. Suppose that astronomers discover a terrestrial-like extrasolar planet that is both very large (and massive), and fairly far away from its parent star. What do you think can be said about this planet? A) It is probably heavily cratered B) It is likely to have an atmosphere C) It probably does not have a magnetic field D) It is probably rotating in retrograde 11. The best evidence that an impact caused the extinction of the dinosaurs is A) At the layer in the fossil record where dinosaurs disappear, there is a large amount of the element iridium, which is common in asteroids, but rare on Earth. B) A large crater has been found which has the broken bones of many dinosaurs inside it. C) Many fist-sized fragments of an asteroid have been found intermingled with the last evidence of dinosaurs in the fossil record. D) Ancient humans recorded the event by making markings on cave walls 12. The temperature of the corona of the Sun A) is about the same as that of the photosphere, 5800 K. B) is about twice as hot as the photosphere, 12,000 K. C) is very cool, because it is farthest from the heat source. D) is very hot about 10 6 K. 13. Which of the following is the brightest as seen from Earth? A) A sunspot B) Venus C) Mercury D) The Moon 14. Thermonuclear fusion reactions in the core of the Sun convert four hydrogen nuclei into one helium nucleus. The helium nucleus has A) less mass than the four hydrogen nuclei, the lost mass becoming energy in an amount given by E = mc 2. B) the same mass as the four hydrogen nuclei, because the mass of any product has to equal the mass of the sum of its parts by the law of conservation of matter. C) an undetermined amount of mass that depends on the temperature at which the reaction occurs D) more mass than the four hydrogen nuclei, because energy is produced in the reaction, and this energy adds the extra mass, m = E/c 2.

5 PTYS/ASTR 206 (Sec. 2) Spring 2007 Mid-Term Exam #2: 3/29/07 (Page 5/7) 15. Why is the planet Mercury so hard to see with the unaided eye? A) it remains close to the Sun in its orbit and is seen in a dark sky only close to the horizon at sunrise or sunset. B) it orbits around the Sun rapidly and moves across our sky very quickly. C) it is a very small object which orbits a long way from the Sun, thereby reflecting very little light back to Earth. D) because of its unusual spin-orbit ratio, when it is at opposition, it is very low in the sky 16. What is principal constituent of the atmosphere of Venus? A) Sulfuric acid B) Methane C) Carbon Dioxide D) Nitrogen 17. Which of the planets best fits the following description: "cool solid surface with an atmosphere of N 2 and O 2 and H 2 O clouds"? A) Mercury B) Mars C) Venus D) Earth 18. About how long is a day on the moon (i.e. the time between two successive sunrises, or sunsets)? A) infinitely long because the Moon does not rotate on its axis B) 1 day, because it always keeps the same side pointing towards Earth C) about 30 days D) about 1 year 19. Which of the terrestrial worlds below are NOT believed to contain at least some water in the form of ice? A) Mercury B) Venus C) The Moon D) Mars 20. Which of the planets fits the following description: "a solid, cool surface, with occasional dust clouds and a thin CO 2 atmosphere"? A) Venus B) Mars C) Mercury D) Earth 21. Mercury appears from spacecraft photographs to resemble the Moon in its surface features. One important difference between these planetary bodies is A) the presence of a measurable and significant atmosphere and clouds on Mercury. B) evidence of active volcanoes on Mercury. C) the presence of extensive plains between craters on Mercury in contrast to the surface of the Moon. D) Mercury's retrograde direction of spin compared to the Moon and most other planets and moons.

6 PTYS/ASTR 206 (Sec. 2) Spring 2007 Mid-Term Exam #2: 3/29/07 (Page 6/7) 22. Mars is best viewed from Earth when it is at opposition. What will be the time interval between two such favorable viewing times? A) 2 synodic periods of Mars, because after every alternate synodic period, Mars will be on the other side of the Sun from Earth. B) 1 sidereal period C) 1 Earth year, the interval between two times when Earth is at a particular position in its orbit. D) 1 synodic period 23. A very brief and intense eruption of hot ionized gas from a sunspot group leading to a short flash of x-rays is a characteristic of A) solar flares B) coronal mass ejections C) the solar wind D) solar neutrinos 24. An ideal steady terrestrial atmosphere is said to be in hydrostatic equilibrium. What does this mean? A) The upward pressure gradient of the atmosphere is balanced by the magnetic force directed downward B) The downward pressure gradient of the atmosphere is balanced by upward heat. C) Incoming solar energy is balanced by the planet s internal energy directed outwards D) The upward pressure gradient of the atmosphere is balanced by downward-directed gravity. 25. During solar maximum, the most dangerous and difficult to shield direct threat to astronauts in space are: A) intense solar magnetic fields B) high-speed solar wind streams C) high fluxes of solar energetic particles accelerated by coronal mass ejections and solar flares D) intense heat from the Sun 26. Only recently has it become known that craters on terrestrial planets are caused by impacts from asteroids and comets. What piece of evidence has led to this realization? A) The discovery of the asteroid belt and many near-earth objects B) The discovery of meteorites inside craters C) The discovery of features in certain quartz crystals that differ from normal quartz, caused by extreme pressures from the impact-induced shock wave. D) The observation of comet Shoemaker-Levy 9 striking Jupiter in Lunar maria are A) large impact craters in-filled by lava B) ancient lake beds, now dry. C) uplifted regions surrounding large shield volcanoes D) heavily cratered highland regions 28. When the solar photosphere is seen with a high-resolution instrument, it is found that there are lightcolored regions surrounded by dark boundaries in a cellular pattern. What are these? A) The cells are regions of nuclear energy generation in the Sun's photosphere. B) The cells are the bases of cyclonic-like circulation patterns that extend from the photosphere to the outer corona. C) Each cell is a region of intense magnetic field that compresses and heats the gas within it D) The cells are the tops of rising blobs of hot gas in the Sun's convective interior

7 PTYS/ASTR 206 (Sec. 2) Spring 2007 Mid-Term Exam #2: 3/29/07 (Page 7/7) 29. Earth's magnetosphere is the A) molten core, whose motions produce the magnetic field. B) region beyond the atmosphere, where the magnetic field protects us from solar wind. C) atmospheric layer between the stratosphere and thermosphere D) the region around industrialized nations having numerous large electrical plants 30. Which two terrestrial planets have no known moons? A) Mars and Mercury B) Mercury and Venus C) Mars and Venus D) Venus and Earth 31. (2-½ pts extra credit). Which statement below about the solar cycle is NOT true? A) The Sun is slightly brighter during solar maximum compared to solar minimum. B) The number of sunspots is greater during solar maximum compared to solar minimum. C) There are more solar neutrinos detected at Earth during solar maximum compared to solar minimum. D) There are fewer galactic cosmic rays arriving at Earth during solar maximum compared to solar minimum 32. (2-½ pts extra credit). On Earth (and in the past, on Mars), volcanoes have been vital for keeping the planet warm. This is because A) heat conducted from the molten mantle to the surface near volcanoes, where the crust is thin, is a major heat source for the atmosphere. B) heat released along the major rift zones is the biggest source of heating for the atmosphere. C) direct heat input by underwater volcanoes keeps the oceans from freezing. D) they have replenished the CO 2 (a greenhouse gas) that is washed out of the atmosphere by rain.