NAME: KEY A. 1. Name three ways in which the planet Uranus is different from the other three gas giants.

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1 PTYS/ASTR 206 (Sec. 2) Spring 2007 Final Exam: 5/10/07 (Page 1/9) NAME: KEY A Part 1: Short Answer (please fill out the answers in the space provided; do not mark the scantron sheet!). Short-answer questions are worth 4 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. Name three ways in which the planet Uranus is different from the other three gas giants. Any of the following (and there are probably others). 1. It is featureless visibly. 2. It is tilted almost completely on its side 3. It receives more solar energy than it radiates (i.e. it does not have a strong internal heat source). 4. It rotates in retrograde about its axis. 2. What is the difference between an absorption spectrum and an emission spectrum? What is the cause of each, respectively? An absorption spectrum is characterized by a series of dark lines within the spectrum of electromagnetic radiation from a source. An emission spectrum is character sized by a series of bright lines. They are both caused by transitions with the atoms as electrons change energy levels. According to Kirchoff s laws, an absorption spectrum results when a continuous spectrum from a bright source passes through a cool dense gas; and an emission spectrum results when the source itself is a hot tenuous gas. 3. What is the best explanation for the occurrence of annually recurrent meteor showers such as the Leonids and Perseids? Earth s orbit intersects the remains of a long extinct comet. The comet broke up due to repeated interactions with the Sun (strong gravitational and tidal forces). What remains is essentially a ring of dust and debris, that intersects Earth s orbit and we simply pass through this every year. 4. Suppose that you went out each day at the appropriate time so that the stars were exactly in the same position that they were the day before. Each day, you also observe how the planet Mars moves relative to this fixed pattern. What will you observe? Be brief, but complete. Mars would generally move eastward most of the time except when it undergoes retrograde motion when it appears to travel westward for a period before turning eastward again. (Over for two more questions)

2 PTYS/ASTR 206 (Sec. 2) Spring 2007 Final Exam: 5/10/07 (Page 2/9) 5. From its center outwards describe the internal structure of Jupiter. From the center outward, Jupiter has a rocky core (also containing perhaps some metals). Then there is a layer of liquid ices, and a layer of helium and liquid metallic hydrogen, then a layer of helium and ordinary liquid hydrogen, and finally the upper atmosphere we see. 6. Ganymede looks similar to our Moon except that we know that the darker terrain is older than the lighter terrain (this is opposite to the case of our Moon). How do scientists know that the darker terrain on Ganymede is older than the lighter terrain? The darker terrain is more heavily cratered. Don t forget more craters implies older surface! Please write below this line only if absolutely necessary

3 PTYS/ASTR 206 (Sec. 2) Spring 2007 Final Exam: 5/10/07 (Page 3/9) Part 2: Multiple Choice Mark the appropriate answer in the appropriate place (i.e. in numbers 1-40) 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 pts each. Two extra-credit questions are the end. 1. Which planet has a mean density lower than water? A) Neptune B) Uranus C) Saturn D) Jupiter 2. The nebular hypothesis of the origin of our solar system explains several physical characteristics of our solar system. Which of these below does this theory NOT explain? A) All planets orbit the Sun in the same direction and in the same plane. B) Terrestrial planets are dense and close to the Sun, and gas giant planets are less dense and far from the Sun. C) Only large and low density gas giant planets have a set of planetary rings D) The Sun is composed mostly of hydrogen and helium. 3. A comet's tails (both the ion and dust tails) are always generally aligned from the comet head in a direction A) away from the Sun B) toward the nearest planet, because of mutual gravitational attraction C) in a direction exactly along the orbital path of the nucleus D) toward the Sun, because of gravitational attraction 4. What two factors account for the strong magnetic fields of Jupiter and Saturn? A) rapid rotation and electrically conducting interiors B) strong convection and iron-rich surfaces. C) atmospheric storms and large mass D) rapid rotation and strong tidal forces. 5. Where is the asteroid belt located? A) Between the orbits of Earth and Mars B) Between the orbits of Mars and Jupiter C) Just beyond the orbit of Neptune extending to a few hundred AU. D) At two of Jupiter s Lagrange points. 6. Asteroids of about 30 meters in diameter strike the Earth roughly every 6000 years or so. What should be expected of such a collision? A) it would destroy all life on the planet B) it would shatter the global economy and lead to the extinction of most of Earth s species C) it would lead to severe effects in the immediate region around the impact, but no global environmental effects D) nothing (other than a brilliant light show), nearly all asteroids of this size burn up in our atmosphere

4 PTYS/ASTR 206 (Sec. 2) Spring 2007 Final Exam: 5/10/07 (Page 4/9) 7. Why are planetary rings so thin? A) Rings consist of particles in Keplerian orbits and because randomly inclined orbits will result in frequent collisions, only flat (thin) rings, where collisions are much rarer, can exist. B) Rings are composed of many charged particles that orbit the planet in a magnetic null point in a very thin region around the equator of the planet. C) Rings are a sheet of solid material held together by self gravity and tidal forces and aligned with the planet s equator. D) The combined gravitational forces of the planet and its moons lead to a thin region around the planet where there are no forces and the ring particles collect there. 8. Which planet rotates on its axis the fastest (i.e. which has the shortest rotational period) in the solar system? A) Mars B) Earth C) Jupiter D) Neptune 9. At what part of the electromagnetic spectrum does the emitted spectrum of planets peak? A) radio B) infrared C) visible D) x-ray 10. If you totaled all of the mass of all of the asteroids in the asteroid belt, you would find it is A) about the same mass as Jupiter B) about the same mass as the Earth C) about the same mass as Mars D) less than the mass of our Moon 11. How are the rotational periods of the interiors of the gas giants determined? A) By observations of the planet s magnetic field (or observations of radio emissions produced by charged particles moving in the magnetic field), which are anchored in the interior. B) By comparing models of the planet s atmospheric circulation to observations of the rotational periods of the cloud tops C) By Doppler imaging of radar signals reflected off of the planet D) They are not yet measured to any accuracy because we cannot land spacecraft on their surfaces, nor can we see any surface details. 12. Both Jupiter and Saturn are significantly oblate. Why? A) Large tidal forces from the Sun have created a huge tidal bulge on them B) Each planet has several large moons whose gravitational effects lead to it having a tidal bulge C) They both rotate very rapidly and have low mean densities D) They both have highly elongated elliptical orbits about the Sun.

5 PTYS/ASTR 206 (Sec. 2) Spring 2007 Final Exam: 5/10/07 (Page 5/9) 13. On which solar system bodies (besides Earth) has liquid water been suggested to exist, either presently or in the past, through indirect spacecraft observations? A) Mercury, the Moon, Europa B) Mars, the Moon, Europa C) Venus, Mars, the Moon D) Mars, Europa, Enceladus 14. In what part of Jupiter s atmosphere do the belts (conspicuous dark, brown-colored, bands that encircle the planet) exist? A) in the magnetosphere, where it is very hot B) in the lower parts of the atmosphere, where it is warmer C) in the upper parts of the atmosphere, where it is cooler D) in the radiative zone 15. What is the Kuiper belt? A) a band of dust in the plane of the ecliptic, extending from near the orbit of Mars to beyond the orbit of Pluto B) the broadest band of asteroids in the asteroid belt, separated from other bands by Kirkwood Gaps C) a relatively flat distribution of icy bodies in the plane of the ecliptic, extending from around the orbit of Neptune out to a few hundred AU from the Sun D) a nearly spherical distribution of icy bodies centered on the Sun and extending to about 50,000 AU 16. Assume you are an astronomer that is observing the occultation of a star by a planet. You observe that the light from the star periodically dims unexpectedly before and after the planet itself passes in front of the star. Which of the following theories best explains the observation? A) The planet has a network of large satellites B) The planet has an extensive, but tenuous, upper atmosphere C) The planet has a very strong magnetic field D) The planet has a ring system 17. Suppose that you are out early one morning with a friend and you see a thin crescent moon low in the eastern sky. Your friend tells you That s cool! It will be a new moon within the next few days. What should be your response? A) No, that s not right. That is a waxing crescent moon and will get bigger over the next few days and in about a week it will be a third-quarter moon. B) Yes, you are right. You must have taken Giacalone s PTYS206 class. C) No, that s not right. That is a waxing crescent moon and will get bigger over the next few days and in about a week it will be a first-quarter moon. D) You may be right, but it depends on whether the Moon is at aphelion (new moon) or perihelion (third quarter moon), or conjunction (first quarter moon). 18. Galileo observed that Saturn s ears occasionally disappeared. What caused this? A) The orientation of Saturn s rings from Earth was seen edge on and since they are very thin, they cannot be seen from Earth. B) Saturn s moon Titan moved in front of the rings and they disappeared from view. C) Saturn moved to a position on the opposite side of the Sun where the rings cannot be seen because of the glare of the Sun. D) Galileo observed the various orientations of Saturn s moons Titan and Enceladus that occasionally give the illusion of disappearing ears

6 PTYS/ASTR 206 (Sec. 2) Spring 2007 Final Exam: 5/10/07 (Page 6/9) 19. What is the Roche limit? A) The maximum thickness of planetary rings. B) The distance of closest approach in the orbit of a moon around a planet C) the minimum size that a moon can be to still be considered a moon D) The distance from a planet where tidal forces acting on a moon exceeds the gravitational forces that hold the moon together. 20. Neptune's predominantly blue appearance is caused by A) the fact that solar light has lost much of its red light by scattering in the interplanetary medium by the time it reaches Neptune. B) auroral emissions caused by solar wind particles exciting the atoms and molecules in Neptune's high atmosphere. C) preferential scattering of the blue end of the solar spectrum by Neptune's atmosphere, similar to the process that causes the blue sky on Earth. D) the absorption of sunlight at the red end of the spectrum by methane in its atmosphere. 21. The larger the orbit about the Sun, the longer it takes for the planet to complete one complete orbital period. Which law is this a consequence of? A) Kepler s first law B) Kepler s third law C) Newton s first law D) Wien s law. 22. Which meteorites are believed to be samples of primordial solar nebula material? A) Iron meteorites B) Stony-Irons C) meteorites showing Widmanstätten patterns when etched with acid D) carbonaceous chondrites 23. What wavelength is the peak in the electromagnetic spectrum of the solar corona? A) Hα B) visible C) infrared D) x-ray 24. The greenhouse effect is the A) trapping of infrared radiation coming from the Sun, and reflected off of Earth, by the atmosphere B) trapping of infrared radiation, emitted by Earth s surface, by the atmosphere C) capturing of visible and ultraviolet radiation from the Sun by the atmosphere D) shielding of life-forms from solar ultraviolet radiation by the ozone layer 25. Which Galilean satellite has a surface that is crisscrossed by numerous fractures, ridges, and cycloidal features that indicate the presence of a subsurface ocean of liquid water? A) Ganymede B) Callisto C) Triton D) Europa

7 PTYS/ASTR 206 (Sec. 2) Spring 2007 Final Exam: 5/10/07 (Page 7/9) 26. From the closest to the farthest away from Jupiter, what is the correct order of the Galilean satellites? A) Io, Ganymede, Europa, Callisto B) Europa, Io, Callisto, Ganymede C) Io, Europa, Ganymede, Callisto D) Io, Europa, Callisto, Ganymede 27. We are currently in the period of solar minimum. What does this mean? A) The Sun s core is near the end of its nuclear burning phase and will soon begin Kelvin-Helmholtz contraction. B) The Earth is at its closest point to the Sun. C) There are very few sunspots on the Sun. D) The number of cosmic rays entering the solar system is at a minimum. 28. Which of the following is the brightest as seen from Earth? A) Saturn B) Venus C) A sunspot D) The Moon 29. The composition of the atmosphere of Titan is mostly. A) methane with small quantities of other gases. B) nitrogen, methane, and other hydrocarbons. C) carbon dioxide with small quantities of other gases. D) methane, ammonia, and water vapor 30. What peculiar feature accompanies Io in its orbit around Jupiter? A) a torus, or ring, of ionized sulfur, oxygen, other atoms, and electrons that are probably related to powerful aurora on Jupiter B) a small Sheppard satellite that shares Io s orbit C) a comet-like tail of rocks and dust, shining by reflected sunlight D) a narrow ring of rocks and dust (Jupiter's ring) at about Io's orbital distance 31. Which of the following statements about Earth s magnetosphere is NOT true? A) It protects the surface from the bombardment of many small asteroids and comets B) It is a cavern carved out of the solar wind by Earth s magnetic field C) It focuses charged particles into Earth s poles and when they impact the atmosphere they create aurorae. D) When it is compressed by a very large solar disturbance it can create significant ground currents that can short out power grids on Earth. 32. How do comets that come from the Kuiper belt differ from those that come from the Oort cloud? A) They have more elliptical orbits B) Their orbits are not as inclined with respect to the ecliptic plane C) They do not form dust tails D) The process of naming them is different.

8 PTYS/ASTR 206 (Sec. 2) Spring 2007 Final Exam: 5/10/07 (Page 8/9) 33. Although we have never seen the Oort cloud, we are quite certain of its presence. Why? A) Most comets have highly inclined orbits and very long periods, suggesting that they originate from a roughly spherical source far from the Sun. B) We have difficulty seeing details of extrasolar planets, so there must be a haze that we cannot see through. C) The orbit of Pluto does not obey Newton s laws, so there must be another massive, undiscovered object that influences its motion. D) Most comets have short periods and orbit near the ecliptic plane indicating they come from a nearly flat source that is not far from the Sun. 34. The discovery of a moon orbiting a planet allows astronomers to measure A) the planet s ring structure B) the moon s mass and density C) the planet s mass D) the planet s cratering history 35. All planetary rings have gaps. What is the cause of these? A) The positions of the particles in the rings are in a resonance with a planet and a major moon which deflects the paths of particles that stray into the gaps B) mutual gravitational interactions between the ring particles C) the intervention of a massive body, which moved through the rings in their early history, leaving the gaps. D) The planet s magnetic field drags particles away from these parts of the rings and into its atmosphere creating aurora 36. The best time to observe fine details of Jupiter through a telescope on Earth is when Jupiter is A) at conjunction, when it appears opposite the Sun and is at its brightest B) just about to rise over the eastern horizon C) between the Earth and Sun, and hence, the largest D) at opposition hence closest to Earth. 37. Which is the most common type of meteorite? A) Stony B) Stony-Iron C) Iron D) Carbon-Nickel 38. Who discovered Pluto? A) William Herschel B) Clyde Tombaugh C) Percival Lowell D) Walt Disney

9 PTYS/ASTR 206 (Sec. 2) Spring 2007 Final Exam: 5/10/07 (Page 9/9) 39. (2 pts extra credit). Suppose that a planet is discovered in the not-to-distant future that is found to have a mass that is twice that of Earth, a density of about 5.5 g /cm 3, and orbits within the habitable zone of its parent Sun. What can be inferred about this planet? A) It is probably terrestrial like with a heavily cratered surface and a tenuous atmosphere of hydrogen and helium. B) It is probably terrestrial like with few craters on its surface and a thick atmosphere C) It is probably a gas giant planet with a thick atmosphere of hydrogen and helium, similar to Jupiter or Saturn (no surface). D) It is probably neither a gas giant nor a terrestrial planet having an icy surface, little or no atmosphere, but possibly a subsurface ocean of liquid water. 40. (2 pts extra credit). Why is it that some asteroids have very low densities (near that of water, like 253 Mathilde whose mean density is 1.3 g/cm 3 )? A) They are composed mostly of ices B) They are composed mostly of rock and ice with a small iron core C) They are composed of a small rocky core, then a layer of liquid hydrogen, followed by an outer atmosphere of ordinary atomic hydrogen D) They are loosely packed ruble piles or rocky material with regions of empty spaces in between.