NAME: CONOR A NIXON - SOLUTIONS
University Of Maryland
Department Of Astronomy
ASTRONOMY 330: The Solar System
EXAM 3 December 19th 2006
1:30 – 3:30 pm (120 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 required. 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 300 points (30% of final grade). Part 1 (75 pts) consists of
short answer questions. Part 2 (75 pts) consists of TRUE/FALSE statements. Part 3 (150
points) consists of longer, structured response questions. There are questions on both
sides of the page. Write all your answers on the exam paper. Extra paper will be provided
on request 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 examination.”
Pledge:
Signed:
-1-
PART 1: SHORT ANSWER QUESTIONS (75 points total).
15 questions. Spend about 2 minutes on each question.
Briefly explain the following five observed facts about the solar system: [5 pts each= 25]
1) All the planets orbit the Sun in the same direction as the Sun spins on its axis, and
nearly in the plane that passes through the Sun’s equator.
This fact indicates that the Sun and planets formed out of the same original
interstellar cloud, which must also have been rotating. Furthermore, it must have
collapsed perpendicular to its spin axis to form a disk, from which the planets came.
2) The inner planets are composed of cosmically rare silicates and metals, while the
outer planets have a composition closer to that of the Sun.
Frictional heating warmed the protoplanetary disk, establishing a temperature
gradient decreasing with radial distance. In the inner parts of the disk, temperatures
were high and only silicates and metals could solidify. In the giant planets region,
temperatures were low enough for ices and volatiles to condense also. Once the
massive cores of the outer worlds formed (10-15 ME), Jupiter and Saturn were able to
accrete directly from remaining gases (solar composition).
3) The existence of the Earth’s oceans, despite the fact that the Earth formed at
temperatures too high for volatiles to have condensed.
The Earth’s oceans are an example of a secondary hydrosphere, which cannot have
formed until after the Earth had cooled sufficiently (original volatiles would have
been lost). The most likely source is cometary delivery, by impacts and otherwise
sweeping up comet tail material.
4) The fact that Venus, Uranus and Pluto do not rotate (spin) in the same direction as
their orbital motion around the Sun.
This fact defies explanation in the disk model. The most likely way that their spin was
altered so greatly is through giant impacts, after they had formed.
5) The gradation in composition within the asteroid belt, from more rocky asteroids
closer to the Sun, to more volatile-rich (carbonaceous) closer to Jupiter.
This again may be a manifestation of the temperature gradient in the protoplanetary
disk: with more silicate rich minerals being prevalent closer to the Sun where
temperatures were higher, and more volatile rich further out, towards Jupiter. A
variation on the theory holds that S-type (inner) asteroids formed in the terrestrial
planet region and were scattered outwards, whereas C-type (outer) asteroids formed
in the giant planet region and were scattered inwards.
-2-
NAME: CONOR A NIXON - SOLUTIONS
PART 1: CONTINUED
6) For each of the following moons, choose from the following list the theory which
best explains its present-day orbit: (A) captured; (B) sister (formed alongside
planet); (C) created by an impact; (D) daughter (split off from planet naturally):
[1 pt each = 5 pts]
(i)
The Earth’s Moon:
C
(ii)
Phobos and Deimos:
A
(iii)
The Galilean satellites of Jupiter:
(iv)
Neptune’s Triton:
(v)
Jupiter’s small irregular satellites:
B
A
A
7) For each of the following dynamical systems, choose from the following list the
theory which best explains its existence: (A) remains of former planet/moon
destroyed in impact; (B) formed in place as appears today; (C) formed elsewhere
composed of objects ejected from elsewhere in the solar system; (D) ejected
material eroding or erupting from a nearby moon. [1 pt each = 5 pts]
(i)
The main asteroid belt:
B or C
(ii)
Saturn’s E-ring:
D
(iii)
The dark rings of Uranus:
(iv)
The Oort cloud:
C
(v)
Jupiter’s dusty rings.
D
A
8) Name two characteristic traits common to most life-forms:
I will accept any two of the following: METABOLISM, GROWTH, ADAPTION,
REPRODUCTION.
[4 pts each = 8 pts]
-3-
9) Order the following in increasing order of chemical/biological complexity:
HUMAN, BACTERIUM, VIRUS, AMINO ACID, FISH, METHANE GAS.
Methane gas, amino acid, virus, bacterium, fish, human. [6 pts]
10) For each of the following mission types, name a famous spacecraft mission of that
type and also the destination planet or moon targeted by that mission.
(There are very many here – I have only listed the most common examples)
(i)
FLYBY MISSION:
TARGET
MISSION NAME
Mercury
Venus
Mariner 10
Mariner 2; Galileo, Cassini;
Messenger
Luna 1 & 3
Mariner 4, 6, 7
Pioneer 10, 11; Voyager 1, 2;
Cassini
Pioneer 11; Voyager 1 & 2.
Voyager 2.
Voyager 2.
none.
Moon
Mars
Jupiter
Saturn
Uranus
Neptune
Pluto
(ii)
ORBITER MISSION:
Mercury
Venus
(none)
Magellan, Pioneer Venus;
Venera 15 & 16; V. Express
Moon
Luna 10; Lunar Orbiters
Clementine; Lun. Prospector;
Mars
Mariner 9, Viking 1&2;
Mars Glob. Surveyor (MGS);
M. Express; M. Odyssey;
M. Recon. Orbiter;
Jupiter
Galileo
Saturn
Cassini
Uran. & Nep. (none)
(iii)
LANDER MISSION:
Mercury
Venus
Moon
Mars
Titan
-4-
(none)
Venera 7, 9, 10, 13, 14, 18
Luna 9; Surveyors 1-7;
Viking 1&2; Pathfinder
Huygens
(iv)
ROVER MISSION:
Moon
Mars
Lunokhod 1
Sojourner; Spirit &
Opportunity
[2 pts for each space mission name and target = 8 pts]
11) Solar system tour operator: imagine you are a 22nd century tour operator, selling
tickets on spacecraft cruises to visit the planets. From the following list of bodies,
choose five that your tour would include, naming one important geological feature
worth seeing in each case that would help sell your tour: MERCURY, MARS,
VENUS, ENCELADUS, IO, EUROPA, IAPETUS, MIMAS, TETHYS,
MIRANDA. Give the geological (Latin) name where possible.
(There are again many possibilities, so I just give the obvious ones)
BODY NAME
MERCURY
MARS
VENUS
ENCELADUS
IO
EUROPA
IAPETUS
MIMAS
TETHYS
MIRANDA
FEATURE
Caloris Basin, Discovery Scarp
Olympus Mons; Arygre Basin; Hellas Basin;
Valles Marineris; Outflow or Runoff Channels;
Gullies; Chaos Terrain; Polar Caps.
Aine Corona; Lakshmi Plateau; Maxwell Mtns;
Pancake Domes
Tiger Stripes (Warm Cracks); South Polar
Geysers.
Loki/Pele/Pillan/Tvashtar Volcanoes.
Scalloped Ridges (Arcs/Flexi); Double (Pressure)
Ridges; Chaotic Terrain.
Cassini Regio (Dark Terrain); Yin-Yang
Coloring
Herschel Crater
Ithaca Chasma; Odysseus Crater/Basin
‘Jigsaw’ terrain.
[2 point for each feature = 10 points]
12) List the following terrestrial events in decreasing order of age (oldest first):
CHICXULUB (impact), TUNGUSKA (event), ALLENDE (meteorite fall),
MOON FORMATION (impact), FIRST CYANOBACTERIA (life).
MOON FORMATION, FIRST CYANOBACTERIA, CHICXULUB IMPACT,
TUNGUSKA EVENT, ALLENDE METEORITE FALL.
[5 points]
[Total for Part I = 72 points].
-5-
NAME:
PART 2: TRUE/FALSE STATEMENTS (75 points total).
6 questions. Spend about 5 minutes on each question.
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 the part of
the statement that is wrong, and write in text that would make the sentence a true,
positive statement.
[Grading: 2 for each statement true/false identification = 60 points; plus 1 point for
each incorrect statement correctly altered to be true = 18 points. Total = 78 pts].
13) RINGS
(a)
 All four of the giant planets are now known to have ring systems,
although none of the inner planets do.
B-ring
(b)
 The Cassini Division separates Saturn’s A-ring from the ribbon-like Fring.
(c)
 Saturn’s broad, diffuse E-ring is the result of water ice particles
streaming off cracks on Europa. Enceladus
(d)
 The F-ring of Saturn is maintained by the co-orbital satellites Janus and
Epimetheus.
(e)
shepherd moons Prometheus and Pandora
 The first clues as to the existence of rings for Uranus and Neptune
were found when astronomers observed stars to flicker on and off as they
approached the planet.
14) TITAN
Ganymede
(a)
 Titan is the largest moon in the solar system. (or Titan is 2nd largest)
(b)
 Titan presents a bland, featureless orange appearance because of its
widespread coverage in sand dunes. atmospheric organic haze/smog.
(c)
 Methane on Titan, like water on the Earth, undergoes a cycle of
evaporation, condensation into clouds, and rainfall onto the terrain.
-6-
(d)
 Titan’s atmosphere is mostly composed of nitrogen gas (N2) like that
of the Earth.
Voyager 1 in 1980
(e)
 The first spacecraft to fly-by Titan was Cassini in 2004.
15) METEORITES
4.6
(a)
 Meteorites usually have ages close to 6.4 Gyr; the age of our solar
system.
(b)
 Meteorites may be classified according to their history/evolution as
primitive, differentiated and breccia types.
differentiated meteorites
(c)
 Stony-iron meteorites are always breccias, because the stony and
metallic pieces become mixed together by impacts.
an equal mixture of right and left
(d)
 Amino acids found in meteorites are predominantly of the right-hand
asymmetric (chiral) form, whereas amino acids from living organisms on
Earth are left-handed.
(e)
 The best place on Earth to hunt for meteorites is Antarctica, because
more meteorites fall on the poles (per square mile) than on the equator.
the white ice makes meteorites easy to spot (and/or because conditions
concentrate them on the surface near mountain ranges)
16) VOLCANISM AND GEYSERS
and Earth are the only places
(a)
 Io is the only place in the solar system where active lava volcanism is
occurring today.
(b)
 Plumes of icy material have recently been spotted erupting from the
north polar ‘tiger stripes’ of Enceladus.
south
(c)
 Lunar rilles are channels carved by ancient lava flows, instead of
water.
(d)
 Geysers have been seen erupting on moons of Jupiter, Saturn and
Neptune, but not on any moons of Uranus.
due to impacts, not volcanoes
(e)
 Most circular lunar craters are found on top of extinct volcanoes.
-7-
NAME:
PART 2: CONTINUED
17) EXTRA-SOLAR PLANETS
(a)
 More planets are now known outside of our solar system than within it.
(b)
 The term ‘hot Jupiters’ applies to all extra-solar planets found around
stars that are hotter than the Sun. in very small orbits around their star
(c)
 The first confirmed discovery of an exoplanet came accidently,
through the precise timing of pulsar radio waves.
(d)
 The search method which has produced the most planet detections so
far is the astrometric method.
radial velocity method (or say that astrometric is the least)
(e)
 The Kepler mission scheduled for launch in 2008 will use the
occultation method combined with a large field of view to detect Earthsized exoplanets.
18) IMPACTS
Uranus’s moon Miranda
(a)
 Saturn’s moon Mimas appears to have been broken apart by a giant
impact and re-assembled by gravity in a random, jumbled-up order.
the last major impact wave about 3.9 to 4.2 Gyr ago
(b)
 The Late Heavy Bombardment was the latest in the series of impacts
waves, and caused the dinosaur extinction 65 Myr ago.
highlands
(c)
 The lunar maria are saturated with impacts, to the point where any new
impact event must eradicate existing impact sites.
(d)
 Venus is the only terrestrial planet that lacks large impact basins,
indicating that its surface is younger than the lunar maria.
(e)
 A layer of iridium metal found in 65 Myr sediments was a crucial
piece of evidence linking the dinosaur extinction to an asteroid impact.
-8-
PART 3: STRUCTURED ANSWER QUESTIONS (150 pts total).
4 questions. Spend about 15 minutes on each question.
19) ENERGY SOURCES
[37 pts]
(a) Is the Sun powered by nuclear fission or nuclear fusion? Briefly describe
in words how the Sun generates its power, mentioning what fuel is used up
and what products are created.
The Sun is powered by nuclear fusion. Its fuel is hydrogen (protons) which it
fuses together by the proton-proton chain, building up heavier nuclei in steps
until a stable helium nucleus is produced (alpha particle). (Helium then builds
up in the core until near the end of the Sun’s life, when a brief helium-burning
period creates carbon). [8 pts]
(b) Define the terms: conduction, convection and radiation. With the aid of a
cross-sectional diagram, label the main layers of the Sun’s interior and say
which heat transport method dominates in each.
CONDUCTION – transfer of heat by molecules banging into each other,
passing along kinetic energy (motion = heat).
CONVECTION – transfer of heat by hot material rising under gravity (less
dense) to a cooler region.
RADIATION – a molecule/atom emits a photon of radiation which carries
away energy to somewhere else.
[3 pts each = 9 pts]
[DIAGRAM: layers of the Sun from center: (1) core (helium) (2)
burning/fusion shell outside core – energy production (3) radiative zone –
energy carried up by photons (4) convection zone – energy convected
upwards (5) surface. Convection is still visible at the surface (granulation).]
[8 pts]
(c) Saturn radiates much more heat energy than it receives from the Sun.
Explain where this energy comes from.
Saturn generates energy through an on-going process of slow differentiation.
Helium droplets condense inside the liquid hydrogen and drift downwards.
Because the helium droplets are more dense than the hydrogen, there is net
conversion of gravitational potential energy to kinetic energy and then heat.
[6 pts]
(d) What is meant by a brown dwarf, and what is the main difference between
a brown dwarf and a planet?
A brown dwarf is a planet between 17 MJ and 0.08 MSUN which can create
some energy through fusing deuterium, and therefore falls between a true
planet (no fusion) and a star (hydrogen fusion).
[6 pts]
-9-
NAME:
PART 3: CONTINUED
20) ECCENTRIC ORBITS
[38 pts]
(a) Describe the orbital differences between short period and long period
comets, mentioning where each type comes from.
SHORT PERIOD COMETS – periods less than 30 years, low orbital
inclinations. Come from Kuiper Belt.
LONG PERIOD COMETS – periods of 200 years or more, any orbital
inclination. Come from Oort cloud.
[5 pts each = 10 pts]
(b) Some asteroids with eccentric orbits may be a danger to life on Earth.
What term is given to these bodies and why are they a danger to us?
These are called Near Earth Asteroids (NEAs) or Near Earth Objects
(NEOs) because their orbits cross the Earth’s. This leaves open the
possibility that some day they may hit the Earth, which apparently does
happen periodically causing mass extinction events, hence the danger.
[9 pts]
(c) Jupiter possesses many irregular moons with elliptical, inclined and/or
retrograde orbits, indicating a different origin to the large Galilean
Satellites. Explain.
The small irregular Jovian satellites are almost certainly captured objects
(cometary nuclei or asteroids), wheras the large Galilean satellites formed
along with Jupiter from a mini-disk (sub-disk) and are all co-planar with
Jupiter equator. Captured comets may have later split apart (by tidal
forces) leading to families of irregular satellites on similar orbits. [9 pts]
(d) Most ring particles are on perfectly circular orbits. Why? Are there
exceptions?
Ring particles need to be on circular orbits, otherwise they will cross the
paths of other ring particles on smaller or larger (semi-major axis) orbits
and either hit them, or gravitationally disturb them. Either way, the
original particle will not long stay in a circular orbit.
[5 pts]
The exceptions are the eccentric rings, which can only maintain eccentric
orbits if they exist in a gap (e.g. Huygens ringlet in the Cassini Division),
or in isolation from other rings (e.g. the F-ring).
[5 pts]
- 10 -
PART 3: CONTINUED
21) LIFE IN THE SOLAR SYSTEM AND BEYOND
[38 pts]
(a) What were atmospheric conditions like on Earth when life first arose some
3.5 Gyrs ago?
Conditions were anoxic (lacking in free oxygen) - the atmosphere was
dominated by CO, N2 and H2O (and CO2 later). The atmosphere was
probably more massive too (higher pressure), and hence had a greater
greenhouse effect and was much hotter.
[8 pts]
(b) How has the atmospheric composition changed from then to now, and
what has caused the changes?
Water dissolved CO2, which then reacted with rocks and became locked
up as carbonate rocks. This reduced the pressure (and temperature)
allowing life to form. Hydrogen also escaped, by photolysis of H2O, CH4
and NH3 at the top of the atmosphere by sunlight, leading to N2 and CO2
becoming the dominant gases. Later, life evolved, producing O2 as a byproduct of photosynthesis. Later life had to evolve respiration in order to
survive in an oxidizing environment.
[12 pts]
(c) What was the significance of the Miller-Urey experiment?
The Miller-Urey experiment was an attempt to replicate or model the
process of organic molecule formation in an early Earth atmosphere. The
experiment reacted H2O, CH4 and NH3 together in a glass vessel under the
action of an electric discharge spark (to simulate lightening) and found
that many organic chemicals were produced, including amino acids. These
molecules are prebiotic, or probable precursors to more complex proteins
and RNA/DNA. So, the significance was in demonstrating that a model
early-Earth atmosphere can give rise to complex, pre-biotic molecules, a
first step perhaps on the road to evolving life.
[10 pts]
(d) What is meant by the ‘impact frustration of life’? Give one or more
examples.
On the early Earth, impacts were much more frequent, larger and more
violent. This may have led to the eradication of early life forms several
times (or more) before the impact rate declined enough for life to take a
permanent foothold which could not be wiped out by later impacts.
However, mass extinctions still occurred, such as the Permian-Triassic
Extinction (250 Myr ago), and the K-T extinction (65 Myrs ago).
[8 pts]
- 11 -
NAME:
PART 3: CONTINUED
22) GALILEAN SATELLITES
[37 pts]
(a) Label the names of Jupiter’s moons A-D on Figure 1 (page 12). Why is
moon A brightly colored while the others are not?
MOON A –
MOON C –
IO
[2 pts] MOON B –
GANYMEDE [2 pts] MOON D-
EUROPA [2 pts]
CALLISTO [2 pts]
COLORING FOR MOON A: Various solid states of pure sulfur (red, yellow,
black) and also white SO2 frost. [4 pts]
(b) A student suggests that moons C&D appear more heavily cratered, and
therefore orbit closer to Jupiter, because impacts become more frequent
deeper in the planet’s gravity well. Do you agree with this explanation? If
not, give an alternate interpretation.
No, I do not agree. Ganymede and Callisto actually orbit further from Jupiter
than do Io and Europa, and must haved suffered less impacts. The real reason
is because the impacts are better preserved over geologic time, because
resurfacing activity decreases outwards from Io through to Callisto. [6 pts]
(c) For each of the layers 1-5 say what is the approximate composition of
material. What evidence is there for layer 3 on moon B?
LAYER 1 -
Rock/metal core.
LAYER 2 –
Silicate magma.
LAYER 3 -
Liquid water.
LAYER 4 -
Rock/ice slush.
LAYER 5 -
Undifferentiated rock/ice solid.
[10 pts]
EVIDENCE FOR LAYER 3: Evidence for Europa’s water layer includes
the surface cracks and flows, the chaos terrain, and the induce magnetic field
(from Jupiter) probably induced in a salty (ionic) ocean layer.
[5 pts]
(d) Why does the proportion of the interior composed of layer 1 decrease from
moon A through moon D, where it disappears entirely?
There are two reasons for vanishing core: (i) decreasing levels of differentiation
going outward from Io to Callisto, and (ii) decreasing proportion of heavy
elements going outwards in the system, from temperature gradients in the original
sub-disk.
[4 pts]
- 12 -
QUESTION 22: CONTINUED
- 13 -