Review for Test #3 April 13 Topics: The Earth and our Moon The Terrestrial Planets The Jovian...
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Transcript of Review for Test #3 April 13 Topics: The Earth and our Moon The Terrestrial Planets The Jovian...
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 test1) Before the Test:• Study hard• Get plenty of rest the night before2) 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
P2 a3 Kepler’s laws, including:
F =G m
1 m
2
R2
Gravitation:
Equivalence of Matter and Energy:
E = mc2
The Structure of the Solar System
~ 45 AU~ 5 AU
L4
L5
L3
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
Crust: thin. Much Si and Al(lots of granite). Two-thirds covered by oceans.
How do we know? Earthquakes. See later
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, innercore solid.
Atmosphere very thin
Earth's Atmosphere
78% Nitrogen21% Oxygen
gas is ionized by solar radiation
ozone is O3 , which
absorbs solar UV efficiently, thusheating stratosphere
commercial jet altitudes
temperature on a cool day
Original gases disappeared. Atmosphere is mostly due to volcanoes and plants!
The Greenhouse Effect
Main greenhouse gases are H
2O and
CO2 .
If no greenhouse effect, surface would be 40 oC cooler!
Global Warming BasicsG
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Humans have increased carbon dioxide (CO2) in the
atmosphere by more
than 35% since the Industrial Revolution.
(National Oceanic and Atmospheric Administration 2006)
The most carbon dioxide in 650,000 years. (IPCC 2007)
(CO2)
10,000 BC 2009
391ppm
EarthquakesThey 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.
But faint P wavesseen in shadow zone,refracting off denseinner core
Curved paths ofP and S waves:density must slowlyincrease with depth
Zone with no S waves:must be a liquid corethat stops them
No P waves too:they must bend sharplyat core boundary
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)
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)
side view
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
TidesA 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
This means: period of orbit = period of spin
Why?Tidal Locking
Earth
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
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.
We always see the same face of the Moon.
The Lunar Surface
- Large, dark featureless areas: "maria" or "seas".
- Lighter areas at higher elevation: "highlands".
maria highlands
- Loads of craters (due mostly to meteorite impacts). No winds to erode them away.
- Highlands have 10x the crater density of maria.
5.1 Earth and the Moon in Bulk
Two Kinds of “Classical” Planets
"Terrestrial"
Mercury, Venus,Earth, Mars
"Jovian"
Jupiter, Saturn, Uranus, Neptune
Close to the SunSmall
Far from the SunLarge
Few MoonsNo RingsMain Elements Fe, Si, C, O, N:we learn that from the spectra
Mostly RockyHigh Density (3.3 -5.3 g/cm3) reminder: liquid water is 1 g/cm3
Slow Rotation (1 - 243 days)
Mostly GaseousLow Density (0.7 -1.6 g/cm3)
Many MoonsRingsMain Elements H, He
Fast Rotation (0.41 - 0.72 days)
The Habitable Zone or “The Goldilocks Problem”In the zone …
Mercury
= 5.4 g/cm3
Mass
Radius
Density
= 3.3 x 1026 g= 0.055 M
Earth
= 2439 km= 0.38 R
Earth
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 KNighttime temp = 100 K
Structure of Mercury
And no atmosphere, so no wind or erosion. Surface reflects geologic history well.
(from Mariner 10 and theoretical arguments)
1.Crust 100-200 km thick
2. Mantle 600 km thick
3. Core, 1800 km in radius
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?
- Hot at surface - 730 K! Almost hot enough to melt rock
- Why so hot? Huge amount of CO2 leads to strong greenhouse
effect.
- 96.5% CO2
- Yellowish color from sulfuric acid clouds and haze.
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.
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?
Impact Craters
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 CO
2 dissolved into
surface water and combined with rocks, then atmospheric and surface water froze (creating ice caps and probable permafrost layer).
The Martian Surface
Valles MarinerisOlympus Mons Tharsis Bulge
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.
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.
(Mars Global Surveyor radar data)
Evidence for Past Surface Water
"runoff channels" or dry rivers
"outflow channels"
teardrop "islands" in outflow channels standing water erosion in craters?
South North
The Jovian Planets (Gas Giants)
Jupiter Saturn
Uranus Neptune
(roughly to scale)
Jupiter
Saturn
Uranus
Neptune
318
95
15
17
Mass (M
Earth)
11
9.5
4
3.9
Radius (R
Earth)
(0.001 MSun
)
Orbit semi-major axis (AU)
Orbital Period (years)
5.2
9.5
19.2
30.1
11.9
29.4
84
164
Major Missions
Voyager 1
Voyager 2
Galileo
Cassini
Launch Planets visited
1977
1979
1989
1997
Jupiter, Saturn
Jupiter, Saturn, Uranus, Neptune
Jupiter
Jupiter, Saturn
Basic Properties
Optical – colors dictated by how molecules reflect sunlight
Infrared - traces heat inatmosphere, therefore depth
So white colors from cooler, higher clouds, brown from warmer, lower clouds. Great Red Spot – highest.
Jupiter's Atmosphere and Bands
Whiteish "zones" and brownish "belts".
Other Jovian planets: banded structure and colors
More uniform haze layer makes bands less visible. Reason: weaker gravity allows clouds torise 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.
- Winds flow in opposite directions in zones vs. belts. Differences are hundreds of km/hr.
- Jupiter's rapid rotation stretches them horizontally around the entire planet.
Jupiter's Internal StructureCan'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:
Jupiter
Saturn
Uranus
Near poles At equator
9h 56m
10h 40m
16h 30m
9h 50m
10h 14m
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"
teardrop "islands" in outflow channels standing water erosion in craters?
South North
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
Closest to Jupiter Furthest from Jupiter
(sizes to scale)
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.
Io Europa Ganymede Callisto
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!