KEY Planetary Sciences 206 -- Section 2 Midterm Examination #2 9:30-10:45 a.m., Tuesday, October 8, 2013 INSTRUCTIONS: There are 35 multiple-choice questions, which are worth 2 points each. The last two questions (#36 and #37) are essay questions, and are worth 15 points each. Mark your multiple-choice answers on this test and on the scantron sheet. CLOSED BOOK, CLOSED NOTES, NO ELECTRONIC DEVICES. 1. Venus has a younger surface than Mars, on average, mainly because m A. the extremely dense atmosphere of Venus prevents resurfacing by impacting objects m B. Venus was formed much more recently than the other terrestrial planets m C. the smaller the body, the more often it will be struck by asteroids and meteoroids l D. Venus produces and stores more heat from radioactive decay than does Mars m E. water erosion is much more important on Venus than on Mars 2. Some scientists think that liquid water can at times be present on Mars because m A. Mars' polar caps melt each spring and fill the canals with water m B. Mars' surface pressure is similar to the Earth's at sea level m C. primordial heat stored in Mars is continuously leaking into space m D. a Viking lander found evidence of artesian springs near the landing site l E. there is geologic evidence that water has occasionally flowed on Mars' surface 3. Which of the following is not related to the fact that the Earth has an iron core? m A. siderophile elements such as iridium are generally rare in the Earth's surface layers m B. there is a "shadow zone" generally opposite an earthquake source where the seismic waves can't go l C. Earth attracts iron meteorites with the same force as rocky meteorites of the same mass m D. the Earth has a global magnetic field m E. the Earth's oblateness is smaller than it would be if the Earth were uniform in density 4. Mercury rotates m A. slowly retrograde m B. rapidly retrograde m C. so as to track Earth at all times m D. so as to track Venus at all times l E. in a 3:2 spin-orbit resonance 5. Venus differs from the Earth in that m A. Venus has no large "continents" m B. Venus has no active volcanoes l C. no water-flow features are seen on Venus m D. Venus has no atmosphere m E. Venus contains no radioactive elements 6. The Earth's surface is generally the youngest among the terrestrial planets because m A. no impacting objects ever made it through the atmosphere m B. solar energy has melted some of the Earth's surface m C. there is no radioactive heat generation in the Earth's interior m D. all of the Earth's surface was underwater until 1 million years ago l E. erosion and plate tectonics continually resurface much of it 7. Which of the following statements is not true? m A. we have seen features on Mars which appear to have been shaped by liquid water erosion m B. we have seen features on the Moon which appear to have been shaped by lava flows m C. we have seen features on Mercury which appear to have been shaped by crustal shrinkage l D. we have seen features on Venus which look like water ice deposits m E. we have seen features on Earth which appear to have been shaped by plate tectonics Page 1 of 6
8. Which of the following statements is not true? m A. we have seen features on Mars which look like water ice deposits l B. the Moon s farside has more mare basins than the nearside m C. we have seen features on Venus which look like impact craters m D. we have seen features on Mercury which look like water ice deposits m E. we have seen features on Earth which look like water ice deposits 9. The basic reason why we see many more craters on the Moon than on Earth is because m A. the Moon efficiently blocks asteroids that might hit Earth m B. on average the Moon receives more sunlight than Earth m C. the Moon orbits outside the Earth s magnetosphere m D. the Earth s surface is very ancient compared with the Moon s l E. the Moon s surface is very ancient compared with Earth s 10. Potassium-40 ( 19K 40 ) is m A. what Argon-40 decays into with a half-life of 1 megayear m B. a manmade element m C. one of the main chemical components of DNA, necessary for life m D. a siderophile element l E. a major radioactive heating source in terrestrial planets 11. How do we know that the Earth's core is as hot as the Sun's surface? m A. tidal dissipation in the Earth's core is so high that this must be what is happening m B. we only know this from theory; there is no way of determining it directly m C. we can see the glow from the Earth's center when we look at lunar eclipses m D. probes that are sent to the Earth's core melt when they get there l E. the iron outer part doesn't transmit S waves, so it must be molten 12. In order for us to use a radioactive isotope to date the oldest solar system minerals, m A. it should have a half-life of about a year m B. it should have a half-life of a few million years m C. it should be present in CAIs l D. it should have a half-life of a few gigayears m E. it should have a half-life of millions of gigayears 13. The boundary of the solar wind m A. doesn't exist; the solar wind goes outward from the Sun to interstellar distances m B. is at a distance of about 30 AU, just inside the orbit of Neptune m C. is at the latitude on the Sun separating slowly rotating polar regions from equatorial regions l D. has been mapped by the Voyager 1 and Voyager 2 spacecraft m E. may be at 100 AU from the Sun but has never been reached by any spacecraft 14. Which of the following statements about Mars is true? m A. probably there was never any liquid water on Mars' surface l B. we can observe dust storms moving across Mars' surface m C. Mars has a global magnetic field much stronger than the Earth's m D. Mars does not have as thick a lithosphere as the Earth m E. as yet we have no Mars specimens that appear to have been in water 15. Our main source of information about the surface geology of Venus is m A. the Pioneer-Venus entry probes m B. visual-wavelength images made with large-aperture telescopes and the Hubble Space Telescope m C. infrared images made with large-aperture telescopes and the Hubble Space Telescope m D. radar maps made with the Arecibo radio antenna in Puerto Rico l E. radar maps made by the Magellan Orbiter 16. Lunar rilles are m A. produced by plate tectonics on the Moon, which continues even today m B. evidence for the absence of any differences in elevation on the Moon in excess of 10 meters l C. ancient, collapsed lava tubes m D. long, straight rays which radiate from big impact structures m E. sounds produced during moonquakes Page 2 of 6
17. Which of the following statements is not true? m A. in general, the bigger the terrestrial planet, the hotter its interior m B. bigger terrestrial planets tend to have younger surfaces m C. our solar system s only terrestrial planet with liquid water on its surface is Earth l D. our solar system s only terrestrial planet with large impact basins is Mars m E. H 2O is only a small fraction of the mass of our solar system s terrestrial planets 18. Which of the following statements about Mars is true? l A. Mars is more massive than Mercury m B. during Martian summer liquid water is present on the surface m C. the biggest volcanoes on Mars are much smaller than big volcanoes on Earth m D. Mars is the smallest terrestrial planet m E. there is no evidence that water ever existed on Mars 19. Which of the following statements about Venus is true? m A. Venus is the smallest terrestrial planet m B. Venus' surface has no impact craters l C. Venus has "continents'' similar to the Earth's m D. there is no evidence for volcanoes on Venus m E. Venus has CO 2 oceans 20. The main difference between the Moon's nearside and farside is m A. the farside is much more geologically recent than the nearside m B. the farside never receives any sunlight m C. the nearside has many more impact craters than the farside l D. the farside has essentially no maria m E. the farside formed at lower temperatures than the nearside 21. A technique for dating samples from the Moon makes use of m A. measurement of the densities of the samples at a temperature of 300 K m B. the appearance of the ablation crusts formed when they entered the atmosphere m C. the absence or presence of CAIs l D. decay of K 40 into Ar 40 m E. measurement of density of micrometeorite craters 22. Which of the following size of impact crater is created most frequently on the Moon's surface? l A. 10 km diameter m B. 30 km diameter m C. 60 km diameter m D. 100 km diameter m E. 200 km diameter 23. Several Saturn 5 third stages (part of the Apollo launch rockets) were deliberately impacted onto the Moon. Why? m A. NASA s planetary quarantine policy required that all nonworking spacecraft be destroyed m B. the television networks demanded a spectacular event during the Apollo missions m C. to add elements to the Moon that could form living organisms l D. to create artificial moonquakes to be used to probe the Moon s interior m E. to study the process of crater formation 24. From a fixed location on the surface of Mercury, the Sun m A. would appear much smaller than it appears from Earth m B. is always in quadrature with the Earth m C. never varies in its apparent size m D. either never rises or never sets, depending on the location l E. rises in the east and sets in the west, as on Earth 25. Water (H 2O) m A. may exist at the base of Mercury s famous scarps m B. has been proved to not exist on Mercury m C. is present in Mercury s tenuous atmosphere l D. may exist at the bottoms of Mercury s polar craters m E. left geological evidence seen in MESSENGER s images Page 3 of 6
26. Water (H 2O) l A. is present in martian polar caps and under polar soils m B. is found in liquid form at the bottoms of some martian craters m C. has never been detected on Mars m D. is now more prevalent on Mars than it was 4 gigayears ago m E. is mostly likely to be found on the peaks of martian volcanoes 27. The following is evidence that the Earth has a liquid outer core: m A. the Earth has the thinnest lithosphere of any of the terrestrial planets m B. the Earth once had a magnetic field but does no longer m C. volcanoes on the Earth's surface erupt liquid iron from the core m D. P-waves can only be seen within 100 km of an earthquake source l E. S-waves don't go through the center of the Earth 28. The source of the Earth s radiation belts is m A. lunar crustal rocks that are enriched in radioactive isotopes m B. contamination from nuclear power plants such as Chernobyl and Fukushima m C. terrestrial crustal rocks that are enriched in radioactive isotopes l D. solar wind plasma captured on Earth's magnetic field lines and then accelerated m E. accidents to RTG-powered spacecraft 29. The difference between saturated and unsaturated cratering is l A. when saturated, each new crater goes over an existing crater m B. the first involves moist soil and the second involves dry soil m C. when saturated, older craters overlie more recent craters m D. saturated cratering is much more common on Earth than on Mercury m E. the first involves volcanism and the second involves impactors 30. The planetary-geology term regolith refers to m A. the outer layers of a planet with a hydrological cycle m B. the region of a planet where the magnetic field arises m C. the most volatile deposits of a planet m D. the equatorial zone of a planet l E. a layer of pulverized rock produced by impacts 31. Impact breccias are typically found m A. in icy polar deposits m B. on the slopes of flow channels l C. in the bottoms of impact craters m D. at the summits of exploding volcanoes m E. in the aerobraking assemblies of spacecraft 32. The half-life for the decay of 19K 40 to 18Ar 40 is 1.28 gigayears. Therefore, l A. when the solar system first formed, there would have been at least 8 times more 19K 40 m B. when the solar system first formed, there would have been at least 8 times less 19K 40 m C. when the solar system first formed, there would have been at least 1000 times more 18Ar 40 m D. 1.28 gigayears from now there will be twice as much 19K 40 m E. potassium-40 cannot be important for producing volcanism in any terrestrial planet at present 33. The following are not seen on the surface of Mars: m A. huge, Arizona-sized volcanoes m B. dendritic flow patterns caused by water streams l C. cryovolcanoes powered by sublimation of nitrogen m D. layered rocks indicative of bodies of water m E. impact craters over 100 km in diameter 34. Earth and Venus have younger surfaces than Mercury, the Moon, and Mars mainly because m A. the dense atmospheres of Earth and Venus prevent resurfacing by impacting objects m B. Earth and Venus were formed much more recently than the other terrestrial planets m C. the smaller the body, the more often it will be struck by asteroids and meteoroids l D. Earth and Venus produce and store more heat from radioactive decay m E. water erosion is much more important on Earth and Venus than on the other bodies 35. The reason that a 100-meter size impactor acts like huge bomb when it hits the Moon is m A. chemicals in its interior react strongly when exposed to lunar matter m B. many meteoroids are made of antimatter, which annihilates ordinary matter on contact l C. its kinetic energy density goes as v 2, and its impact velocity v is greater than 2.4 km/sec m D. it is accelerated strongly by the solar wind as it approaches the Moon m E. it has been heated to 900 K in space by solar ultraviolet photons Page 4 of 6
FIRST ESSAY QUESTION Write your answers in the spaces provided; use the back of this form if necessary. 36. All Mars lander experiments, successful or otherwise, have been aimed at the northern hemisphere of Mars. Explain why this choice was made. (15 pts.) Mars is both Earthlike and Moonlike Like the Moon, Mars is divided into old, heavily cratered highlands and younger, lightly cratered lowlands. It has two provinces: ancient, heavily-cratered highlands (similar to the Moon's) located mainly in the southern hemisphere younger plains located mainly in the northern hemisphere. It is the lower, younger northern plains that show evidence of ancient water flows, and evidence of subsurface water deposits. Since Mars exploration has a major goal of looking for ancient life on Mars and evidence of habitability, all surface lander experiments have been in the north, the region that has the best chance of success. Page 5 of 6
SECOND ESSAY QUESTION Write your answer in the space provided; use the back of this form if necessary. 37. What is the evidence that Mercury has a large iron core? (15 pts.) The mean density of Mercury (5.4 g/cm 3 ) is about the same as the Earth's, although Mercury is much smaller (only 0.055 of the Earth's mass). Because of this high mean density, researchers believe that Mercury has a large iron core. There is also geological evidence (scarps) on Mercury that suggests the presence of a core. Mercury shows evidence of crustal shrinkage, not seen on the Moon, which may be related to the cooling of its iron core. Mercury has an intrinsic magnetic field, which may be generated by electrical currents in the core. Page 6 of 6