Exam2.html

Astronomy 105.01 Second Examination Wed., October 29, 1997

Name:___________________________________________________________

Honor Pledge:

This exam consists of 36 questions and is worth a total of 100 points.

This exam is due at 10:25. You may use a calculator, but no notes or reference books.

Part I. Multiple choice. Each question is worth 2 points.

1. Which space mission did not visit Jupiter?
a. Galileo.
b. Voyager 2.
(c.) Magellan.
d. Pioneer 10.

2. The lowest layer of the Earth's atmosphere is called the
a. ozone layer.
b. stratosphere.
(c.) troposphere.
d. atmosphere.

3. Which of the following is not produced by plate tectonics?
a. midocean rifts
b. earthquakes
c. volcanoes
(d.) Earth's magnetic field

4. The greenhouse effect keeps Venus hot because
a. the atmosphere contains free oxygen.
(b.) the atmosphere is rich in carbon dioxide.
c. the surface is free of sulfur compounds.
d. the magnetic field traps a large number of particles from the solar wind.

5. The flow patterns found on the surface of Mars suggest
a. that Mars is a water-rich world.
(b.) that the climate on Mars was different in the past.
c. that volcanism is occurring on Mars.
d. all of the above

6. The canals of Mars were found to be
a. irrigation ditches dug by Martians.
b. faults in the Martian crust.
c. sinuous rilles
(d.) an optical illusion.

7. By what mechanism does radiation reach the Sun's surface from its interior?
a. Ionization.
b. Neutrinos.
(c.) Convection.
d. The solar wind.

8. Why do we see fewer craters on earth than on the moon?
a. Only moons have craters.
b. The earth was never hit by many meteorites.
c. The earth is harder than the moon and meteorite impacts left no craters.
(d.) Surface erosion has obliterated most craters.

9. Granulation is caused by
a. sunspots.
(b.) rising gas below the photosphere.
c. shock waves in the corona.
d. the solar wind flowing away from the corona.

10. Mercury's surface resembles that of what other world?
a. Earth.
(b.) The Moon.
c. Mars.
d. Venus.
e. Pluto.

11. The geology of Venus appears to be dominated by
(a.) volcanism.
b. plate tectonics.
c. impact cratering.
d. strip mining.

12. The minor planets or asteroids are located
(a.) mainly between Mars and Jupiter.
b. mainly beyond Pluto.
c. in orbit around Jupiter.
d. fairly evenly throughout the solar system.

Part II: True/False. Each question is worth 2 points.

1. Most of the visible light from the sun originates in the photosphere.

(T) F

2. The greenhouse effect occurs because carbon dioxide is opaque to infrared radiation.

(T) F

3. Few, if any, of the craters on the Moon are the result of volcanism.

(T) F

4. Due to their large sizes and masses, the Jovian planets have higher densities than the Terrestrial planets.

T (F)

5. Valles Marineris is a long valley on Mars believed to resemble the rift valleys of eastern Africa.

(T) F

6. NASA has committed itself to placing humans on the Moon again before the turn of the century.

T (F)

7. Lava from volcanic eruptions originates in the core of the Earth.

T (F)

8. Rainfall is the most important type of surface evolution on Venus.

T (F)

9. After stopping at Mars, the Viking probes went on to Jupiter and Saturn.

T (F)

Part III. Fill in the Blank. Each question is worth 2 points.

1. The slow motion of the continental plates on Earth is called_____________.
CONTINENTAL DRIFT or PLATE TECTONICS

2. The principle constituent of the atmospheres of Venus and Mars is ______.
CARBON DIOXIDE

3. __________ was the mission to Venus which mapped over 99% of the surface using radar.
MAGELLAN

4. The ____________ of Mars contain mostly frozen carbon dioxide.
POLAR CAPS

5. Besides Earth, which of the terrestrial planets and/or satellites of terrestrial planets show(s) evidence for the possible existence of liquid water flowing on its surface in the past? ________________
MARS

6. The most massive planet in the solar system is______.
JUPITER

7. The _____ are huge, dark, lava-filled regions on the Moon.
MARIA or SEAS

8. The ______ is the outward flow of charged particles leaving the Sun.
SOLAR WIND

9. The most prevalent element in the Earth's atmosphere is _____________.
NITROGEN

10. ________ was the name of the space program which put a man on the Moon.
APOLLO

Part IV: Calculations. Each question is worth 4 points. The formulae given at the bottom of the next page may be useful. Be sure to include units for each answer.
You must show your work for full credit.

1. What is the mass of Mercury? Its radius and density are given at the bottom of the next page.

Use the formula relating mass to density and volume.
M = p V. p= density = 5400 kg/m3
Calculate volume V using V = (4/3)pi R3 = (4/3)(pi)(2,450,000 m)3 = 6.16 X 1019 m3
Putting this together gives M = (5400 kg/m3)(6.16 X 1019 m3) = 3.3 X 1023 kg.

2. What is the escape velocity from the Moon?

The formula for escape velocity is
Ve = Square Root [ 2 G M / R ].
After converting to proper units we have:
G = 6.67 X 10^-11 N-m²/kg²
M = 7.4 X 10²² kg
R = 2.439 X 10⁶ m
Ve = Square Root [4.04 X 10⁶] = 2000 m / s = 2 km / s.

3. Cassini left the Earth traveling at approximately 11 km/s, just above the escape velocity for the Earth. Assuming that Cassini travels straight to Saturn at a constant speed, how long will it take for this probe to reach Saturn?

Use the formula v = d / t , and solve for t = d / v .
t = (1.27 X 10⁹ km) / (11 km / s) = 1.1 X 10⁸ s = 3.7 years.

4. What is the angular size, q, of the Valles Marineris on Mars when Mars is closest to Earth? The Valles Marineris is 4000 km long.

This problem uses the small-angle formula:
(q / 206,265") = (d / D)
We are solving here for q, the angular size of the Valles Marineris.
q = (d / D )(206,265") = (4000 km / 7.5 X 10⁷ km) (206,265") = 11" (arc seconds).

5. Kepler's Third Law allow us to find the mass of a planet from observing the motion of its moon. The mass of a planet in solar masses, M , is equal to the ratio: a 3 / P 2, where a = the orbital radius of the moon in AU and P = the period of the moon's orbit in years . Use this formula to find the mass of the Earth in solar masses. For the Moon,
a = 0.00256 AU and the period of the orbit is 27.3 days.

Use the formula M = a³ / P².
We are given a = 0.00256 AU
and we can convert p = (27.3 d) / (365 d / y ) = 0.0748 years.
Thus M = (0.00256)³ / (0.0748)² = 3 X 10^-6 Solar masses.

1 year = 3.15 X 10⁷ s Closest distance from Earth to Saturn = 1.27 X 10⁹ km
(q / 206,265") = (d / D) Closest distance from Earth to Mars = 7.5 X 10⁷ km
G = 6.67 X 10^-11 N-m²/kg² Ve = Square Root [ 2 G M / R ]
Mass of the Moon = 7.4 X 10²² kg Radius of the Moon = 2439 km
Density of Mercury = 5400 kg/m³ Radius of Mercury = 2450 km
M = r V V = (4/3) p R³ 1 AU = 1.5 X 10⁸ km v = d / t
Part V: Short answer. Each question is worth 3 points.

1. What are the names of the terrestrial planets? Roughly how far is each from the Sun in AU?

MERCURY: 0.4 AU
VENUS: 0.7 AU
EARTH: 1.0 AU
MARS: 1.5 AU

2. Briefly describe the fusion process by which the Sun produces its energy.

FOUR PROTONS ARE FUSED TOGETHER IN FIVE REACTIONS TO FORM A HELIUM-4 NUCLEUS. TWO POSITRONS AND TWO NEUTRINOS ARE ALSO PRODUCED. ENERGY IS RELEASED BECAUSE THE MASS OF THE HELIUM NUCLEUS IS LESS THAN THE SUM OF THE MASSES OF THE FOUR PROTONS. MASS IS CONVERTED TO ENERGY BY EINSTEIN'S EQUATION: E = M C2.

3. In the diagram below, label the major divisions of the interior of the Earth.

A = CRUST
B = MANTLE
C = OUTER LIQUID CORE
D = INNER SOLID CORE

4. Discuss the atmosphere of Venus and how it keeps the surface so hot.

THE ATMOSPHERE OF VENUS IS MOSTLY CARBON DIOXIDE WHICH TRAPS HEAT FROM THE SUN WITHIN THE ATMOSPHERE THROUGH A RUNAWAY
GREENHOUSE EFFECT.

5. What are the four predominant theories of the origin of the Moon? Which one is considered most correct?

COFORMATION THEORY; CAPTURE THEORY; FISSION THEORY;
CONSIDERED MOST CORRECT IS THE IMPACT THEORY

6. Identify the features below by type of feature and solar system body on which they are found.

FROM TOP TO BOTTOM,

SPLASH CRATER ON MARS

CORONAE ON VENUS

SUNSPOTS ON THE SUN