Test Instructions

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Test Instructions

• Do not sit in the last two rows!
• Write your name and three-digit ID on both the
  test and the answer sheet and fill in the
  bubbles.
• Use only a 2 pencil.
• Make sure you have a different colored test from
  anyone sitting right next to you.
• Fill in your answers on both the test and answer
  sheet.
• Turn in both items to the box of the appropriate
  color.

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Two Kinds of Planets
"Terrestrial"
"Jovian"
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Two Kinds of Planets
"Terrestrial" Mercury, Venus, Earth, Mars
"Jovian" Jupiter, Saturn, Uranus, Neptune
Distance from Sun? Size? Composition? Density? Rot
ation Rate? Number of moons? Rings? Heavy or
light elements?
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Origin of Pluto
Now known to be just the largest of a class of
objects in the outer reaches of the Solar System
The Kuiper Belt Objects
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Questions

• What are some of the smaller objects (or debris)
  found in the solar system?
• What is the main reason that we study these
  smaller objects? (What information do they
  contain that the planets and moons do not?)

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Questions

• What are some of the smaller objects (or debris)
  found in the solar system?
• Comets, asteroids, meteoroids
• What is the main reason that we study these
  smaller objects? (What information do they
  contain that the planets and moons do not?)
• Solar system debris is unevolved gt gives direct
  evidence of conditions during solar system
  formation!

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Comet Structure
Nucleus 10 km ball of ice, dust Coma cloud of
gas and dust around nucleus (106 km
across) Tail can have both ion and dust tails
(108 km long). Always points away from Sun.
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Solar System Formation
Our solar system started out as a giant cloud of
cold gas that collapsed under its own
gravity. So, why is our solar system flat?

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Conservation of angular momentum!
What role did dust play in the formation of our
solar system?
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Condensation theory 1) Dust grains act as
"condensation nuclei" gas atoms stick to them gt
growth of first clumps of matter. Also radiate
heat gt help to cool gas gt faster gravitational
collapse. What term describes the process by
which smaller particles collide and stick
together to form larger clumps?
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Condensation theory 1) Dust grains act as
"condensation nuclei" gas atoms stick to them gt
growth of first clumps of matter. Also radiate
heat gt help to cool gas gt faster gravitational
collapse. 2) Accretion Clumps collide and
stick gt larger clumps. Eventually, small-moon
sized objects "planetesimals". 3)
Gravity-enhanced accretion objects now have
significant gravity. Mutual attraction
accelerates accretion. Bigger objects grow
faster gt a few planet-sized objects.
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Greenhouse Effect

• What is the greenhouse effect and how does it
  differ on Earth and on Venus?

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Runaway Greenhouse Effect on Venus
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The Interior of the Earth

• How does temperature vary as we get closer to the
  core of the Earth?
• What about density?

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Earth's Internal Structure
Temperature and density increase with increasing
depth. How do we obtain information about the
structure of the Earth's interior?
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Like all waves, seismic waves bend when they
encounter changes in density. If density change
is gradual, wave path is curved. S-waves are
unable to travel in liquid. Measurement of
seismic waves gives info about density of Earth's
interior and which layers are solid/molten.
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The Tides

• What causes the tides?
• When are the highest (and lowest) tides seen?

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Tides
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Questions

• What are the two main features of the lunar
  surface? Which is older? How do we know?
• What is currently the most widely excepted theory
  explaining how the moon formed?

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The Lunar Surface

• Large, dark featureless areas "maria" or
  "seas". More recent lava flows.
• Lighter areas at higher elevation "highlands".
• Many craters (due to meteorite impacts). Only
  important source of erosion!
• Highlands have 10x the crater density of maria
  gt Highlands are older!

highlands
maria
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Impact Theory Early in Solar System, when
many large planetesimals around, a Mars-sized
object hit the forming Earth, ejecting material
from the mantle which went into orbit around
Earth and coalesced to form Moon. Computer
simulations suggest this is plausible.
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Properties of the planets

• Which planet exhibits retrograde rotation?
• How do we determine the direction and rate of a
  planet's rotation?

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Anomalous rotation of Venus

• Extremely slow - Venutian day longer than
  Venutian year!
• Retrograde - Sun rises in the west and sets in
  the east!
• Most likely due to a collision during solar
  system formation

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Determining rotation rate of a planet

• Use reflected radio waves to determine line of
  sight doppler shifts.

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Venus

• Thick clouds prevent viewing of surface. (UV
  Image)
• High temperatures and pressures, acidic gases,
  make it difficult to land anything on surface.
• Led to much speculation.
• How did we get info about surface?

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"Radar Mapping" technique measures altitude
space probe
time for signal to return tells you the altitude
of surface feature.
Planet Surface
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Properties of the Planets
Which planet has the largest known volcano in
the solar system?
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Mars

• What is the main reason that many scientists
  think Mars may have once harbored life?
• What is the most likely origin of the two moons
  of Mars?

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Evidence for Past Surface Water
"runoff channels" or dry rivers
"outflow channels"
teardrop "islands" in outflow channels
standing water erosion in craters?
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Mars' Moons Phobos and Deimos
Deimos 16 x 10 km
Phobos 28 x 20 km
Properties similar to asteroids. They are
probably asteroids captured into orbit by Mars'
gravity.
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Question

• Jupiter and Saturn were known to the ancient
  astronomers. Uranus, which is barely visible to
  the naked eye, was discovered in 1781.
• Neptune is not visible to the naked eye, so how
  was it discovered?

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Discovery of Neptune
Neptune predicted to exist because of
irregularities in Uranus' orbit. Neptune
discovered in 1845 by Johann Galle. Gravitational
perturbation of Uranus orbit by unseen planet
led to discovery of Neptune! Keplers and
Newtons laws in action! Nice example of how
the scientific method works!
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Question

• Zones and belts are, respectively, high and low
  pressure systems on Jupiter.
• What process would you expect to be taking place
  between such regions?
• Why do the zones and belts stretch all the way
  around Jupiter?

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- Zones and belts are Jupiter's high and low
pressure systems, respectively. - They mark a
convection cycle. - Jupiter's rapid rotation
stretches them horizontally around the entire
planet. - Gas in zones and belts flow in opposite
directions.
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Differential Rotation

• What is differential rotation and what types of
  objects rotate in this way?

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Differential Rotation
Rotation period of Jovians is shorter closer to
the equator
Near poles
At equator
9h 50m 10h 14m 14h 12m
9h 56m 10h 40m 16h 30m
Jupiter Saturn Uranus
How do we know? Tracking storms at various
latitudes, or using Spectroscopy and Doppler
shift.
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The Galilean Moons of Jupiter
(sizes to scale)
Furthest from Jupiter
Closest to Jupiter
Would you expect Jupiter to be hotter or cooler
very early in its history? What might this imply
for the Jupiter-Galilean moon system?
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The Galilean Moons of Jupiter
(sizes to scale)
Furthest from Jupiter
Closest to Jupiter
The Galilean Moons resemble a miniature planetary
system in many ways! Intense heat of young
Jupiter played role of sun.
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Io's Volcanism
More than 80 volcanoes have been observed. Can
last months or years. Largest is bigger than
Maryland - emits more energy than all Earth
volcanoes combined! Io is about the size of our
moon. Why is it's volcanic activity surprising?
Where is the energy coming from?
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Io and Europa are in a resonance orbit
Start clock now
Jupiter
Europa
Io
One orbit of Io
Jupiter
Europa
Io
The periodic pull on Io by Europa makes Io's
orbit elliptical and distorts entire moon.
Two orbits of Io
Jupiter
Io
Europa
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Jovian Rings

• How did Saturn's rings form?

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Origin of Saturn's Rings
If a large moon, held together by gravity, gets
too close to Saturn, the tidal force breaks it
apart into small pieces. The radius where this
happens is called the Roche Limit. Total mass of
ring particles equivalent to moon 250 km in
diameter.
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Voyager probes found that rings divide into
10,000's of ringlets.
What maintains this ringlet structure?
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Shepherd Moons

• Some ringlets maintained by gravitational
  influence of shepherd moons
• Keep particles from straying outside the path of
  the ringlet