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Review for Test #3 April 13
Topics:
• The Earth and our Moon
• The Terrestrial Planets
• The Jovian Planets
• Moons, Rings, Pluto, Comets, Asteroids, Dust, etc.
Methods
• Conceptual Review and Practice Problems Chapters 5 - 8
• Review lectures (on-line) and know answers to clicker & HW questions
• Try practice quizzes on-line (in MA)
•Bring:
• Two Number 2 pencils
• Simple calculator (no electronic notes)
Reminder: There are NO make-up tests for this class
Test #2 Review
How to take a multiple choice test
1) Before the Test:
• Study hard
• Get plenty of rest the night before
2) During the Test:
• Draw simple sketches to help visualize problems
• Solve numerical problems in the margin
• Come up with your answer first, then look for it in the choices
• If you can’t find the answer, try process of elimination
• If you don’t know the answer, Go on to the next problem and
come back to this one later
• TAKE YOUR TIME, don’t hurry
• If you don’t understand something, ask me.
Test #2 Useful Equations
Kepler’s laws, including:
P2 is proportional to a3
Gravitation:
F=
G m1 m2
R2
Equivalence of Matter and Energy:
E = mc2
The Structure of the Solar System
L3
L5
L4
~ 5 AU
~ 45 AU
Oort Cloud is a postulated huge, roughly spherical reservoir of comets
surrounding the Solar System. ~108 objects? Ejected planetesimals.
A passing star may dislodge Oort cloud objects, plunging them into
Solar System, where they become comets.
If a Kuiper Belt object's orbit takes it close to, e.g., Neptune, its
orbit may be changed and it may plunge towards the inner Solar
System and become a comet.
Earth's Internal Structure
How do we know? Earthquakes. See later
Crust: thin. Much Si and Al
(lots of granite). Two-thirds
covered by oceans.
Mantle is mostly solid, mostly
basalt (Fe, Mg, Si). Cracks in
mantle allow molten material
to rise => volcanoes.
Core temperature is 6000 K.
Metallic - mostly nickel and
iron. Outer core molten, inner
core solid.
Atmosphere very thin
Earth's Atmosphere
78% Nitrogen
21% Oxygen
Original gases disappeared. Atmosphere is
mostly due to volcanoes and plants!
gas is ionized by
solar radiation
ozone is O3 , which
absorbs solar UV
efficiently, thus
heating stratosphere
commercial jet
altitudes
temperature on a cool day
The Greenhouse Effect
Main greenhouse
gases are H2O and
CO2 .
If no greenhouse
effect, surface
would be 40 oC
cooler!
Global Warming: The Greatest Threat © 2006 Deborah L. Williams
Global Warming Basics
 Humans have
increased carbon
dioxide (CO2) in the
atmosphere by more
than 35% since the
Industrial
Revolution.
391ppm
(CO2)
(National Oceanic and Atmospheric
Administration 2006)
 The most carbon
dioxide in 650,000
years. (IPCC 2007)
10,000 BC
2009
Earthquakes
They are vibrations in the solid Earth, or seismic waves.
Two kinds go through Earth, P-waves ("primary") and S-waves ("secondary"):
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.
Thus, measurement of seismic wave gives info on density of Earth's
interior and which layers are solid/molten.
Zone with no S waves:
must be a liquid core
that stops them
But faint P waves
seen in shadow zone,
refracting off dense
inner core
No P waves too:
they must bend sharply
at core boundary
Curved paths of
P and S waves:
density must slowly
increase with depth
Earthquakes and volcanoes are related, and also don't occur at random
places. They outline plates.
Plates moving at a few cm/year. "Continental drift" or "plate tectonics"
When plates meet...
1) Head-on collision
(Himalayas)
side view
2) "Subduction zone"
(one slides under the other)
(Andes)
3) "Rift zone"
(two plates moving apart)
(Mid-Atlantic Ridge)
4) They may just slide past each other
(San Andreas Fault)
top view
=> mountain ranges, trenches, earthquakes, volcanoes
What causes the drift?
Convection! Mantle slightly fluid and can support convection.
Plates ride on top of convective cells. Lava flows through cell
boundaries. Earth loses internal heat this way.
Cycles take ~108 years.
Plates form lithosphere (crust and solid upper mantle).
Partially melted, circulating part of mantle is asthenosphere.
5.7 Magnetospheres
The magnetosphere is the region around Earth where
charged particles from the solar wind are trapped.
5.7 Magnetospheres
These charged
particles are trapped
in areas called the
Van Allen belts,
where they spiral
around the magnetic
field lines.
The Moon
Tides
A feature of oceans (but solid material has small tides too).
Two high and two low tides per day.
Tides are due to Moon's gravitational pull being stronger on
side of Earth closest to it (Sun causes smaller tides).
Earth-Moon gravity keeps them
orbiting each other. But side of Earth
closest to Moon has slightly stronger
pull to Moon => bulges towards it.
Other side has weaker pull => bulges
away compared to rest of Earth.
The Earth spins once a day while the
bulge always points towards and away
from the Moon => high and low tides.
Tides
We always see the same face of the Moon.
This means: period of orbit = period of spin
Why?
Tidal Locking
The tidal bulge in the solid
Moon elongates it slightly (2-3
km) along an axis pointing to
Earth.
Top view of Moon
orbiting Earth
Earth
If orbit period faster than spin
period, tidal bulge would have to
move around surface of Moon,
creating friction, which slows
the Moon’s spin down until tidal
bulge no longer migrates around.
The Lunar Surface
- Large, dark featureless areas:
"maria" or "seas".
- Lighter areas at higher
elevation: "highlands".
- Loads of craters (due mostly
to meteorite impacts). No
winds to erode them away.
- Highlands have 10x the crater
density of maria.
maria
highlands
5.1 Earth and the Moon in Bulk
Two Kinds of “Classical” Planets
"Terrestrial"
"Jovian"
Mercury, Venus,
Earth, Mars
Jupiter, Saturn,
Uranus, Neptune
Close to the Sun
Small
Mostly Rocky
High Density (3.3 -5.3 g/cm3)
reminder: liquid water is 1 g/cm3
Slow Rotation (1 - 243 days)
Few Moons
No Rings
Main Elements Fe, Si, C, O, N:
we learn that from the spectra
Far from the Sun
Large
Mostly Gaseous
Low Density (0.7 -1.6 g/cm3)
Fast Rotation (0.41 - 0.72 days)
Many Moons
Rings
Main Elements H, He
The Habitable Zone or
“The Goldilocks Problem”
In the zone …
Mercury
Mass = 3.3 x 1026 g
= 0.055 MEarth
Radius = 2439 km
= 0.38 REarth
Density = 5.4 g/cm3
Semimajor axis = 0.39 AU
Discovery of Water Ice on
Mercury
Goldstone 70m radar received by
the VLA
Polar regions could be 125 K and
never warmed by the Sun
Orbit of Mercury
3:2 resonance with the sun
Orbital period of 88 days
Sidereal rotation of 59 days
1 “day” on mercury = 176 earth
days
Daytime temp = 500 K
Nighttime temp = 100 K
Structure of Mercury
(from Mariner 10 and theoretical arguments)
1.Crust 100-200
km thick
2. Mantle 600 km
thick
3. Core, 1800 km
in radius
And no atmosphere, so no wind or erosion.
Surface reflects geologic history well.
Venus
Mass = 0.82 MEarth
Radius = 0.95 REarth
Density = 5.2 g/cm3
Average distance from Sun = 0.72 AU
Orbital period = 225 days
Rotation period = 243 days (longer
than orbital period, and retrograde!)
Venus' Atmosphere
- Pressure at surface is 90 x that of Earth's => much more gas in
atmosphere. No oceans.
- Consequence - meteoroids burn up easily. No impact craters less
than ~3 km. What’s the composition of the atmosphere?
- 96.5% CO2
- Yellowish color from sulfuric acid clouds and haze.
- Hot at surface - 730 K! Almost hot enough to melt rock
- Why so hot? Huge amount of CO2 leads to strong greenhouse
effect.
Early on, T may have been much lower (but still warmer than Earth).
Oceans existed?
But if warm enough, T would start to rise because of...
Runaway Greenhouse Effect
1) Water and CO2 evaporate from oceans into atmosphere.
2) Greenhouse effect more efficient.
3) Temperature rises.
4) More evaporation (back to #1).
=> complete evaporation of oceans. Thick atmosphere.
Impact Craters
Unlike Moon, larger impact craters distributed randomly over surface =>
all parts of surface have about same age.
Paucity of large impact craters => surface is young, 200-500 million years?
Volcanism
Shield volcano elevation map from Magellan radar data. About 100 km across.
Volcanism may be ongoing, based on sulfur dioxide variations in atmosphere.
But very little resurfacing in past 200-500 million years.
Venus surface flyover
Mars
Mass = 0.11 MEarth
Radius = 0.53 REarth
Density = 3.9 g/cm3
Average distance from Sun = 1.52 AU
eccentricity = 0.093
Range in distance from Sun = 1.38 1.66 AU
Rotation Period = 24.6 hours
Orbital Period = 687 days
The Martian Atmosphere
- 95% CO2
- Surface Pressure 0.006 that of Earth's atmosphere (thin air!)
- Surface Temperature 250 K.
- Dust storms sometimes envelop most of Mars, can last months.
A “Reverse Runaway Greenhouse Effect”? During volcanic
phase (first two billion years), thicker atmosphere, warmer
surface, possibly oceans. Gradually most CO2 dissolved into
surface water and combined with rocks, then atmospheric and
surface water froze (creating ice caps and probable permafrost
layer).
The Martian Surface
Olympus Mons
Tharsis Bulge
Valles Marineris
Southern Hemisphere ~5 km higher
elevation than Northern, and more
heavily cratered.
South is like lunar highlands, surface
~4 billion years old, North like maria,
~3 billion years old.
Valles Marineris - 4000 km long, up to
7 km deep. Ancient crack in crust.
Reasons not clear.
(Mars Global Surveyor radar data)
Tharsis Bulge - highest (10 km) and
youngest (2-3 billion years) region.
Olympus Mons - shield volcano,
highest in Solar System, 3x Everest in
height. 100 km across.
Evidence for Past Surface Water
"runoff channels" or
dry rivers
"outflow
channels"
South
standing water erosion in craters?
North
teardrop "islands" in
outflow channels
The Jovian Planets (Gas Giants)
Jupiter
Saturn
Uranus
Neptune
(roughly to scale)
Basic Properties
Mass
(MEarth)
Jupiter
Radius
(REarth)
Orbit semi-major axis Orbital Period
(AU)
(years)
318
11
5.2
11.9
Saturn
95
9.5
9.5
29.4
Uranus
15
4
19.2
84
Neptune
17
3.9
30.1
164
(0.001 MSun)
Major Missions
Launch
Voyager 1
1977
Planets visited
Jupiter, Saturn
Voyager 2
1979
Jupiter, Saturn, Uranus, Neptune
Galileo
1989
Jupiter
Cassini
1997
Jupiter, Saturn
Jupiter's Atmosphere and Bands
Whiteish "zones" and brownish "belts".
Optical – colors dictated by how
molecules reflect sunlight
Infrared - traces heat in
atmosphere, therefore depth
So white colors from cooler, higher clouds, brown from warmer, lower
clouds. Great Red Spot – highest.
Other Jovian planets: banded structure and colors
More uniform haze layer makes
bands less visible. Reason:
weaker gravity allows clouds to
rise higher and spread out to
create more uniform layer
Blue/green of Uranus and blue
of Neptune due to methane.
Colder than Jupiter and Saturn,
their ammonia has frozen and
sunk lower. Methane still in
gas form. It absorbs red light
and reflects blue.
- Zones and belts mark a convection cycle. Zones higher up than belts.
- Zones were thought to be where warm gas rises, belts where cooled gas sinks.
Now less clear after Cassini, which found numerous upwelling white clouds in
the dark belts.
-
- Jupiter's rapid rotation stretches them horizontally around the entire planet.
- Winds flow in opposite
directions in zones vs.
belts. Differences are
hundreds of km/hr.
Jupiter's Internal Structure
Can't observe directly. No seismic information. Must rely on physical
reasoning and connection to observable phenomena.
(acts like a liquid metal,
conducts electricity)
Core thought to be molten or partially molten rock,
maybe 25 g/cm3, and of mass about 10-15 MEarth .
Other Jovians similar. Interior temperatures, pressures and densities less
extreme.
Differential Rotation
Rotation period is shorter closer to the equator:
Near poles
At equator
Jupiter
9h 56m
9h 50m
Saturn
10h 40m
10h 14m
Uranus
16h 30m
14h 12m
How do we know? Tracking storms at various
latitudes, or using Spectroscopy and Doppler shift.
Evidence for Past Surface Water
"runoff channels" or
dry rivers
"outflow
channels"
South
standing water erosion in craters?
North
teardrop "islands" in
outflow channels
Storms on Jovian Planets
Jupiter's Great Red Spot: A hurricane
twice the size of Earth. Has persisted for
at least 340 years.
New storm “Oval BA”
Neptune's Great Dark Spot: Discovered by Voyager 2 in 1989. But
had disappeared by 1994 Hubble observations. About Earth-sized.
Why do storms on Jovian planets last so long?
On Earth, land masses disrupt otherwise smooth flow patterns. Not a
problem on Jovian planets.
The Galilean Moons of Jupiter
(sizes to scale)
Io
Closest to Jupiter
Europa
Ganymede
Callisto
Furthest from Jupiter
Radii range from 1570 km (Europa, slightly smaller than our Moon), to 2630
km (Ganymede - largest moon in Solar System).
Orbital periods range from 1.77 days (Io) to 16.7 days (Callisto).
The closer to Jupiter, the higher the moon density: from 3.5 g/cm3 (Io) to 1.8
g/cm3 (Callisto). Higher density indicates higher rock/ice fraction.
Saturn's Rings (all Jovians have ring systems)
- Inner radius 60,000 km, outer radius
300,000 km. Thickness ~100 m!
- Composition: icy particles, <1 mm to
>10m in diameter. Most a few cm.
- A few rings and divisions distinguishable
from Earth.
Study hard and do well!