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KEY
Planetary Sciences 206 -- Section 2
Midterm Examination #4
9:30-10:45 a.m., Thursday, December 5, 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.
1. A striking phenomenon which shows the influence of Jupiter on asteroid orbits is
m A. the large number of asteroids with sizes larger than 500 km
l B. the Kirkwood gaps, for example at 1:3 orbital period:Jupiter
m C. the Oort cloud
m D. the Doppler effect observed in most asteroid spectra
m E. the Roche limit when applied to asteroid Ida
2.
m
m
m
m
l
The estimated number of comets in the Oort cloud is
A. about 102
B. about 104 to 105
C. fewer than 107
D. more than 107 but fewer than 108
E. about 1013
3. Select the correct statement
m A. if all the asteroids were gathered together, they would make a planet bigger than Earth
l B. the asteroids which orbit farthest from the sun tend to be the most primitive
m C. there seem to be no asteroids that are smaller than 200 km in diameter
m D. asteroids orbit in a spherical distribution around the Sun, similar to the outer Oort cloud
m E. the total number of known asteroids is about 500
4.
m
m
m
Meteorites that most resemble the Moon's mare basalts in composition are
A. carbonaceous chondrites
B. ordinary chondrites
C. iron meteorites
l D. achondrites
m E. tektites
5. The main reason that most comets are not observed more than a few AU from Earth is
m A. few comets have orbits with semimajor axes greater than a few AU
l B. most comets develop tails only inside the "frost line"
m C. most comets are in loose orbits about the Earth
m D. their tails can only be seen in forward-scattered light
m E. they move too fast to be detected when they are at distances greater than a few AU
6. The amount of energy required to place 1000 kg in Earth orbit is
m A. 1/10 of the energy required to place 100 kg in Earth orbit
m B. the same as the energy required to place 100 kg in Earth orbit
l C. 10 times the energy required to place 100 kg in Earth orbit
m D. 100 times the energy required to place 100 kg in Earth orbit
m E. 1000 times the energy required to place 100 kg in Earth orbit
7. The proportion of N2 in the Earth's atmosphere
m A. is similar to the N2 proportion in Neptune's visible atmosphere above the clouds
m B. is the result of biological activity on the earth
m C. is similar to the N2 proportion in Venus' atmosphere
m D. represents about 20% of the atmosphere by number of molecules
l E. represents most of the atmosphere, similar to Titan, Triton, and Pluto
8. The so-called "rock clouds" that have been hypothesized for Jupiter's deep atmosphere
m A. were directly observed by the Galileo Entry Probe
l B. have been detected in hot "Jupiters" orbiting other stars
m C. have been proven not to exist
m D. have been seen in Pluto's atmosphere only
m E. are only seen where the temperature is less than 100 K
9. Which of the following statements about Pluto is true?
l A. Pluto has a thin nitrogen atmosphere at present
m B. Pluto only develops an atmosphere when it is farthest from the Sun
m C. Pluto was visited by a spacecraft in 1989
m D. Pluto has no known satellites
m E. Pluto is officially recognized as the ninth planet
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10. The CAI material in the Allende meteorite
m A. is a sample of extraterrestrial life
l B. was created at a very high temperature
m C. appears in the form of round, glassy spherules
m D. is dark, earthy, and carbonaceous
m E. is evidence that Allende comes from Mars
11. Which of the following statements is true?
m A. there is no definite evidence yet for a planet outside our solar system
m B. giant planets like Jupiter cannot exist closer than 5 AU from their star
m C. debris disks are never observed in young solar systems
m D. our solar system is the only one we know with Jupiter-mass planets
l E. there is evidence of enhanced radioactivity when our solar system formed
12. Some meteorites contain decay products from radioactive isotopes of aluminum, iodine, and plutonium that
m A. were produced by contamination from nuclear weapons testing
l B. were produced in exploding stars before the solar system formed
m C. have half-lives of about one gigayear
m D. have larger abundances, the younger the meteorite and the more iron it contains
m E. are most frequently found in basaltic achondrites
13. Which of the following statements about Triton is not true?
m A. Triton's surface is coated with layers of frozen volatiles
m B. Triton is in a retrograde orbit around Neptune
l C. Triton's surface shows channels formed by liquid H2O
m D. Triton appears to be forming a secondary atmosphere of N2
m E. Triton is the largest satellite of Neptune
14. Planetary scientists have been able to monitor Triton's atmosphere by
m A. measuring the effects as Triton passes in front of the Sun
l B. observing occultations of stars by Triton
m C. observing the appearance of CH4 clouds in its atmosphere
m D. using yearly spacecraft encounters with Triton and measuring radio occultations
m E. sending probes to Triton in 1995 and 1997
15. One similarity between Pluto, Triton, and a typical comet is
m A. all have orbital radii of about 30 AU
l B. all develop volatile atmospheres in response to sunlight
m C. all have similar sizes
m D. all of these objects are on independent orbits around the Sun
m E. all have orbits that are strongly influenced by Jupiter
16. A planet orbiting at 30 AU will intercept, compared to the Earth,
l A. 1/900 as much solar power per square meter of surface
m B. 1/30 as much solar power per square meter of surface
m C. (1/30)1/2 as much solar power per square meter of surface
m D. (30)1/2 as much solar power per square meter of surface
m E. 302 as much solar power per square meter of surface
17. The oldest, most primitive meteorite that we examined in class was
m A. the Tucson meteorite
m B. a piece of Allan Hills 84001
m C. a piece of Canyon Diablo
m D. a piece of Odessa
l E. a piece of Allende
18. Planet Earth has had intelligent, space-faring life forms for about
m A. 10-4 of Earth's time of existence
m B. 10-5 of Earth's time of existence
m C. 10-6 of Earth's time of existence
m D. 10-7 of Earth's time of existence
l E. 10-8 of Earth's time of existence
19. The reason that siderophile elements are relatively rare on the Earth's surface is
l A. they have been mostly incorporated in the Earth's core
m B. they were mostly lost with the nebular gas when it dissipated
m C. they are radioactive with a relatively short half-life
m D. we know that they are depleted in primitive objects from which the Earth formed
m E. terrestrial biological processes have depleted them
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20. The number of known planets is about
m A. eight
m B. nine
m C. ten
m D. twelve
l E. one thousand and counting
21. The leading cause of death among college-age Americans is
m A. side effects of global warming
m B. environmental effects of meteoroid impacts
m C. ozone poisoning
m D. transport in common carriers (airlines, train, bus, etc.)
l E. vehicular accident
22. One of the reasons that impact of a large meteoroid onto the Earth can be devastating to life is
m A. it releases a lot of hydrogen and helium into the atmosphere
l B. huge amounts of dust and nitric acid are produced
m C. the crater traps creatures who accidentally wander into it
m D. it carries an unusual amount of the element osmium, which is highly poisonous
m E. it changes the Earth's orbit very significantly
23. The reason that asteroids have not collected to form a planet is because
m A. their parent body only exploded 1 gigayear ago and they haven't had time
m B. they are so spread out that gravity can't take effect
m C. they do not have any chemical resemblance to terrestrial planets
l D. they are close to Jupiter, which keeps disrupting their orbits
m E. most of them are closest to Earth, which collects them instead
24. The reason that a 100-m sized meteoroid releases so much energy when it hits the Earth is
m A. chemicals in its interior react strongly when exposed to the Earth's atmosphere
m B. many meteoroids are made of antimatter, which annihilates ordinary matter on contact
l C. its energy density goes as v2, and the impact velocity v is 11 km/sec or more
m D. it is accelerated strongly by the solar wind just before it reaches the Earth
m E. it has been heated to 900 K in space by solar ultraviolet photons
25. The escape velocity from Jupiter is about six times the escape velocity from Earth. Therefore
l A. a comet that hits Jupiter will release about 36 times as much energy as the same comet hitting Earth
m B. a comet that hits Jupiter will release about 6 times as much energy as the same comet hitting Earth
m C. a comet that hits Jupiter will release about 3 times as much energy as the same comet hitting Earth
m D. a comet that hits Jupiter will release about 1/3 as much energy as the same comet hitting Earth
m E. a comet that hits Jupiter will release about 1/6 times as much energy as the same comet hitting Earth
26. A siderophile element that was detected in unusual abundance in the Cretaceous-Tertiary boundary layer was
l A. Iridium
m B. Magnesium
m C. Calcium
m D. Xenon
m E. Plutonium
27. The isotope Al26 has a half-life of 106 years. After 2 X 106 years, what fraction of the original number is left?
m A. none
m B. 1/2
l C. 1/4
m D. 1/8
m E. 1/16
28. If a space station were placed at the Earth's leading Lagrange point L4,
l A. it would always be where the Earth would be two months later
m B. it would end up at Mars as a result of tidal forces
m C. it would be torn apart by tidal forces from the Moon
m D. it could only see one side of the Earth
m E. it would soon end up on a collision course with Venus or Mercury
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29. An asteroid's orbit has a semimajor axis a = 4 AU. The asteroid's orbital period is
m A. indeterminate from the information given
m B. 2 Earth years
m C. 4 Earth years
l D. 8 Earth years
m E. 16 Earth years
30. The reason that most satellites of the giant planets are icy is:
l A. the giant planets are beyond the solar system's water frost line
m B. they started in the terrestrial planet zone and then migrated beyond 5 AU
m C. giant planets can only form satellites when large concentrations of N2 are present
m D. satellites only form when the planet has free neon in its atmosphere
m E. ice can only form in high-gravity environments
31. An icy body with a radius of 200 km orbiting in a circular, prograde, low-inclination orbit 45 AU from the Sun
l A. is a Kuiper Belt object
m B. is a Trojan asteroid
m C. is a typical long-period comet
m D. is a typical P-type asteroid
m E. could not exist because it would quickly vaporize
32. The main difference between a brown dwarf and a planet like Jupiter is
m A. brown dwarfs don't contain very much hydrogen
m B. the radius of a brown dwarf is at least 10 times bigger than Jupiter's radius
m C. a brown dwarf is another name for a dwarf planet like Pluto
m D. we have never actually seen a brown dwarf -- they're just theoretical at present
l E. a brown dwarf can have thermonuclear fusion of deuterium at its center
33. The term "orbital resonance'' means
l A. the ratio of two orbital periods is as the ratio of two whole numbers
m B. the distance between two orbits is a whole number of AU
m C. the same side of Mercury always points to the Earth when Mercury is closest to the Earth
m D. the orbit is gradually decaying due to atmospheric drag forces
m E. orbits which are distant from the Sun have higher eccentricities
34. Comets usually cease activity as they move far away from the Sun because
m A. the vapor pressure of their volatiles rises, and they outgas more
l B. the vapor pressure of their volatiles falls, and they outgas less
m C. terrestrial observers can no longer see them clearly
m D. they suffer collisions with the jovian planets
m E. they never reach distances greater than about 100 AU from the Sun
35. Which of the following planets has no CO2 detected in its atmosphere?
m A. Earth
m B. Venus
m C. Mars
lm D. Pluto
m E. CO2 has been detected in the atmospheres of all planets
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ESSAY QUESTIONS
Write your answers in the spaces provided; use the back if you need more room.
36. Discuss the probable appearance (size, composition) and activity (gases and particles in its vicinity) of a typical long-period
comet with a periapse distance of 0.4 AU and an apoapse distance of 100000 AU at the following points in its orbit:
apoapse: 5 pts.
Nucleus only. No activity. Temperature below 30 K. Nucleus about 1 to 10 km in size,
composed of solid ices mixed with dust particles.
about 4 AU from the Sun: 5 pts.
Activity due to sublimation of water starts, as water vapor pressure rises to a few
millibars. Formation of a coma, and jetting from surface. Nucleus surface begins to lose
volatiles.
periapse: 5 pts.
Maximum activity. Coma formed from jets of vapor from surface vents. Tails of ions and dust
particles carried off with the gas are formed. Ion tail points directly away from Sun, while dust tail
is distributed more along orbit. Nucleus surface continues to lose volatiles.
37. NASA is currently devoting many resources to the search for extraterrestrial life. Planetary scientists think that the single most
important environmental factor relevant to whether life might exist in a given location in the solar system is the existence of liquid
water.
(a) Name three locations in the solar system (other than Earth) where liquid water might be present. 6 pts.
1. below the surface of Mars
2. below the icy surface of Europa (below the icy surface of Ganymede is also ok)
3. in cloud particles at pressures of a few bars in the atmospheres of Jupiter, Saturn, and possibly
Uranus and Neptune
(b) For each of these locations, give the evidence that leads scientists to think that liquid water might be present. 9 pts.
1. High-resolution images from Mars Global Surveyor show mysterious "seeps" in the walls of
some canyons and craters. According to one interpretation, these were made by subsurface
water on Mars. According to the water phase diagram, water must be at a pressure higher than
the triple point to be liquid, and the temperature must be above the melting curve. These
conditions might exist below the Martian surface.
2. High-resolution images from Galileo show evidence of recent resurfacing of the outer layer of
Europa, and we know that Europa has an outer layer of water 100 to 200 km thick. If the
temperature rises to about 250 K at the bottom of this layer, there might be an ocean. (As
mentioned in lecture, Ganymede's magnetic field also suggests the possibility of a liquid "water
sandwich" below Ganymede's surface.)
3. In Jupiter's troposphere, the temperature rises to about 300 K, above the melting point of
water, at pressures of a few bar. If water can condense into droplets in this region, it could be
liquid. There may be similar conditions in the deep tropospheres of the other giant planets.
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