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!

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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!