Download NAME: CONOR A NIXON - Solutions

NAME: CONOR A NIXON - Solutions
University Of Maryland
Department Of Astronomy
ASTRONOMY 330: The Solar System
EXAM 2 November 7th 2006
12:30 – 01:45 (75 minutes)
Room CSS 2428
INSTRUCTIONS:
Read these instructions carefully before turning over.
This is a closed book exam: no notes, books or any other information materials may be
used. No calculators allowed. Use blue or black ink, write as neatly as you can. Do not
use correction fluid. Cross out any writing or calculations which you do not want to be
graded. No talking or communicating with other students during the exam. If you need to
ask a question of the invigilators raise your hand.
This exam has 3 parts, totaling 200 points (20% of final grade). Part 1 (50 pts) consists of
short answer questions. Part 2 (50 pts) consists of TRUE/FALSE statements. Part 3 (100
points) consists of longer, structured response questions. There are questions on both
sides of the page. Write all your answers on the exam paper. There is extra space at the
end if you need to continue any answer beyond the space provided.
Write your name at the top of each exam page, and any extra pages you use.
Read each question carefully twice through before you begin writing.
HONOR PLEDGE: (copy the honor pledge below and sign)
“I pledge on my honor that I have not given or received any unauthorized assistance
on this assignment/examination.”
Pledge:
Signed:
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PART 1: SHORT ANSWER QUESTIONS (50 points total).
1. Name three of the four types of boundaries that can occur between plates of the
Earth’s crust, and give a brief description of the processes occurring in each case.
Any three of the following: [4 pts each x 3 = 12 pts]

Rift Zone: this is an area where two plates are moving apart, such as the midAtlantic ridge.

Subduction Zone: occurs where one plate slides under another (typically the
ocean crust goes under the continental crust), e.g. the deep trenches off the
coast of Asia.

Fold Mountain Range: e.g. the Himalayas. Occurs where two plates collide and
neither one goes under, typically two continental plates.

Fault line: where two plates scrape against each other in a parallel direction, e.g.
the San Andreas fault of California.
2. Rank the four outer planets in each of the following categories:
[2 pts each x 5 = 10 pts. Partial credit awarded for partial correct ordering]
(a) ORBITAL DISTANCE (furthest from Sun to closest):
Neptune, Uranus, Saturn, Jupiter
(b) DIAMETER (largest to smallest):
Jupiter, Saturn, Uranus, Neptune
(c) MASS (highest to lowest):
Jupiter, Saturn, Neptune, Uranus
(d) DENSITY (highest to lowest):
Neptune, (Jupiter & Uranus tied), Saturn
(e) ROTATION PERIOD (longest day to shortest):
Uranus, Neptune, Saturn, Jupiter
3. Describe two other physical ways (other than those in the previous question) in
which Jupiter and Saturn differ substantially from Uranus and Neptune.
Possibilities include: [5 pts each x 2 = 10 pts]




Cloud cover: U&N exhibit much less prominent clouds and banding than
J&S. No ammonia ice clouds – CH4 clouds instead.
Bulk Composition: much higher proportion of rocks and ices, and less
hydrogen and helium for U&N compared to J&S.
Atmospheric composition: more CO and N2, less hydrated gases such
as NH3, PH3.
Internal structure: no metallic hydrogen layer or helium rain.
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NAME:
4. Briefly describe one piece of evidence for the presence of running, liquid water
(not ice) on Mars at each of the following two times: [5 pts each x2 = 10 pts]
(a) In the past: Either:
i. RUNOFF CHANNELS – networks of drainage channels similar to
terrestrial rivers, found in southern cratered uplands on ancient
terrain and thought to be about 4 Gyr old. (OR)
ii. OUTFLOW CHANNELS – huge valley systems much larger than
the runoff channels, leading from the southern uplands out onto
the northern plains. Thought to be due to huge floods, caused by
the heating/melting of underground reservoirs, about 3.5 Gyr ago.
(b) Today: GULLIES – freshly cut small gullies on the walls of some craters
and runoff channels. The crispness of the edges and the fact that the
debris overlies windblown sediments indicates that these are very recent,
probably continuing intermittently today.
5. GEOGRAPHY QUIZ: identify which solar system body is the home of each of
the geologic features below. Bonus extra credit: name the feature!
(a) MOON – HADLEY RILLE (2+2 PTS)
(b) VENUS – AINE CORONA (2+2 PTS)
(c) MARS – OLYMPUS MONS (2+2 PTS)
(d) MERCURY – CALORIS BASIN (2+2 PTS)
(1 PT IF YOU WROTE MOON)
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PART 2: TRUE/FALSE STATEMENTS (50 points total).
Be the professor! In each case, circle the letter for correct statements, and cross out the
letter for incorrect statements. Then for all the incorrect statements, cross out part of the
sentence, and write text that would make the sentence into a true, positive statement.
[2 pts for each statement correctly categorized as TRUE/FALSE x 15 = 30 pts, plus 2 pts
for modifying incorrect statements to make them correct x 10 = 20 pts. Total 50 pts]
6. MAGNETOSPHERES
(a)
 Magnetic fields trap charged particles from the solar wind, directing them
towards the planetary poles, where they cause aurorae.
(b)
 Jupiter and Saturn have strong magnetic fields, due to electrical currents
circulating in their molten interior layers of nickel-iron. metallic hydrogen.
(c)
 Planetary magnetic fields are always aligned with the rotation axis of the
planet.
(d)
can be at any possible orientation to
 The fact that Mars today has only a weak magnetic field may be explained by
the theory that the field is currently transitioning from north to south polarity.
a residual magnetic field has ‘frozen into’ the surface rocks
(e)  Charged particles spiraling along magnetic field lines cause radio emissions
from Jupiter and Saturn.
7. SURFACES
Imbrium
(a)  The impact that created the Orientalis Basin on the Moon blanketed the nearside in a debris layer known as Fra Mauro material.
(b)
 The surface of Mercury appears similar to the Lunar highlands, with many
craters, but no large impact basins have yet been discovered.
and at least one impact basin (Caloris) known so far
(c)  Scarps on Mercury probably formed as the planet cooled and shrunk,
compressing surface material.
(d)
 The tallest features on Mars, Venus and the Earth are all shield volcanoes.
but the tallest features on Earth and Venus are fold mountains
(e)  The Valles Marineris (Mariner Valleys) on Mars were probably caused by the
erosive action of a river, much like the Earth’s Grand Canyon.
faulting/rifting and subsequent enlargement by erosion, unlike the
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NAME:
8. INTERIORS
(a)
 The main reason for the excess heat radiated by Saturn and Jupiter, over and
above the heat they receive from the Sun, is due to the slow contraction of the
entire planet. the separation and condensation of helium droplets within the liquid
hydrogen, a process known as ‘helium rain’
(b)
 The core of Mars consists primarily of iron sulfide, rather than iron-nickel as
for the Earth.
S-waves
(c)  P-waves (pressure waves) cannot travel through liquids such as the earth’s
outer core, whereas S-waves (shear waves) can traverse liquids.
P-waves
(d)  Mercury has a weak magnetic field about 1% as strong as that of the Earth’s,
and is due to surface rocks having become permanently magnetized in the past.
a partially molten metal core
(e)  Mantle plumes are thought to be responsible for both Venusian Coronae, and
the Tharsis Uplift on Mars.
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PART 3: STRUCTURED ANSWER QUESTIONS (50 pts each question, 100 pts total).
9. CRATERING
(i)
In 1892, USGS geologist Grove Gilbert proposed that lunar craters were not
volcanic in origin, as then thought, but produced by impacts. Why had the
volcanic theory of crater formation been favored until then, and what
evidence did Gilbert propose to overturn it?
The volcanic theory had prevailed principally by analogy with the Earth: all
craters known on the Earth at that time were volcanic, and in addition no
near-Earth asteroids were known, so there was no plausible population of
impactors in the inner solar system. [6 pts]
Gilbert noted that lunar craters do not occur on top of mountains, and that the
floors lie below the level of the surrounding plains. This then destroyed the
analogy with Earth’s volcanic craters, and impacts became the only favored
explanation. [6 pts]
Gilbert’s impact hypothesis suffered from one major drawback that he could
not explain at the time: what was the problem, and how was it eventually
explained?
(ii)
The major problem with Gilbert’s theory was that lunar craters were uniformly
round. The understanding of cratering at the time was based on the ‘sandbox
analogy’, in which different shapes of craters should be produced by objects
impacting from different angles. Therefore, all lunar craters would have to be
produced by impacts from directly overhead, which seemed highly unlikely.
[6 pts]
The problem was with the analogy: a meteoroid strike is actually much more
like a bomb blast than a stone thrown in a sandbox, due to the immense
amount of energy released by the projectile. The blast destroys any evidence
on the original direction of travel of the meteoroid. This became understood in
the 20th century. [6 pts]
(iii) Describe three features seen in complex craters that are not present in simple
craters. Use a sketch to illustrate your answer.
Complex craters may have the following features not seen in simple craters:
[3 pts x 2 = 6 pts]





Central peak, or for basins a peak ring or rings.
Collapsed/terraced rim.
Secondary craters from ejecta.
Lava-flooded floors (or sediment covered on Earth)
Lower height to width ratio of 1/10 or less, compared to 1/5 for simple
craters.
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NAME:
Question 9 continued.
The sketch should approximate the one below. [10 pts]
(iv) Describe the appearance of craters found on Mars. What are the (a)
similarities and (b) differences to lunar craters?
(a) Similarities: [5 pts]
i. raised and terraced rrims
ii. flat depressed (flooded) floors
iii. central peaks or peak rings
iv. etc etc
(b) Differences: main difference is in the ejecta blanket. Whereas lunar ejecta
blankets show evidence of ballistic material – including: rays, streaks and
secondary crater chains – martian ejecta blankets appear fluidized. Two
forms are commonly seen:
i. ‘Flower pattern’ – shows lobate flow, with multiple lows evident,
and each lobe bounded by a steep, smooth edge.
ii. ‘pancake form’ – a smooth pancake of material with a slightly
scalloped rim.
[5 pts]
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10. ATMOSPHERES
(i)
Look at the Earth’s atmospheric temperature profile below, and then name
the Regions A-D and Boundaries 1-3. [7 pts]
(ii)
Why does the temperature fall as we ascend in Region A, and rise again
with height in Region B?
In Region A, temperature falls due to convection: warm air near the Earth’s
surface is less dense and rises, transporting heat upwards. As it does so, the air
cools by expansion and temperature falls.
[5 pts]
In Region B, temperature rises due to absorption of solar UV radiation by ozone,
which is re-radiated as heat.
[5 pts]
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NAME:
Question 10 continued.
(iii) Explain the Earth’s greenhouse effect. Is it a good thing?
The Earth’s greenhouse effect is due to the atmosphere being more transparent
to visible light radiation than to heat. Visible light penetrates to ground level,
where it is absorbed and becomes heat. UV light is absorbed in the stratosphere.
However, IR (heat) radiation is blocked by molecules, including CO2, H2O, O3,
CH4 and others, which creates a ‘blanket’ effect to keep heat in. [10 pts]
The natural greenhouse effect is good in sense that without it, the Earth’s surface
would be up to 25-30C colder, and so all the water would freeze, with dramatic
implications for life. However, too much of a good thing can be bad… if the manmade or anthropogenic greenhouse was to increase temperatures a lot, the
climate may become less suitable for humans over much of the planet. A major
danger is of melting all the polar caps, and flooding most major cities which are
coastal. [7 pts]
(iv) Compare and contrast the greenhouse effects on Mars and Venus with that
of the Earth.
The greenhouse effect on Venus is much stronger than on the Earth, contributing
a temperature increase of over 500K compared to the equilibrium temperature of
230K (if it had no atmosphere at all). The main greenhouse gas is CO2, which
constitutes 97% of the atmosphere. Venus has suffered a runaway greenhouse
effect, in which increases in temperature have tended to increase the amount of
atmospheric CO2, in turn increasing the size of the greenhouse effect, and so on.
The main underlying cause is simply Venus’ proximity to the Sun. [8 pts]
Mars has a much thinner atmosphere (0.08 bar) than the Earth (1.0 bar), which is
in turn much thinner than that of Venus. Hence, there is only a tiny greenhouse
effect at Mars. Much of Mars’ atmosphere has escaped due in part to its smaller
gravity. The atmosphere is CO2 like Venus, but not enough of it to contribute
significant warming. [8 pts]
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EXTRA WRITING AREA
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