ISP 205, Section 3, Spring 2003, Prof. Stein

UNIT II: THE PLANETS

OUTLINE

This outline will be revised as this unit procedes.

A. Overview of the Solar System B. The Terrestrial Planets and the Moon C. The Jovian Planets D. Formation of the Solar System E. Life in Other Planetary Systems

A. Overview of the Solar System

Reading: sections 4.1, 4.2

Orbits: nearly circular; lie in nearly same plane (ecliptic plane)(disk shaped); Voyager demo
Two types of Planets: Terrestrial - inner, small, density of rock, rocks and iron
Mercury, Venus, Earth, Mars; Jovian - outer, large, density of water, hydrogen, helium and ices
Jupiter, Saturn, Uranus, Neptune
Asteroids and comets

Links:

http://seds.lpl.arizona.edu/nineplanets/nineplanets/overview.html

Diagrams:

                                     AST disk
             size of orbits          10357    (re US map)
                                     10359
                                     10361    (Earth-Jupiter)
                                     10362    (Jovian)
             inclination of orbits   10365
             tilt of rotation axis   10366

Images:

                         Beyond Earth      Astronomy
      Mercury               311              10345
      Venus clouds          312              10346
      Venus surface         313 (radar)      11101-11105, 10386
      Earth                 314              10347, 10387
      Moon                  315              11629
      Mars                  1011             10348, 10388
      Jupiter               320              10349
      Saturn                323              10350
      Uranus                324
      Neptune               325

B. The Terrestrial Planets and the Moon

Comparative Planetology - Terrestrial Planets
Reading: Chapters 5, 6
see also: The Nine Planets and Views of the Solar System

Composed of rocks and iron. High densities. Small masses. Inner planets.

1. Surface

Reading: sections: 5.7, 5.4, 6.4 - 6.6

a. Earth
Reading: Chapter 5

See also: Views of the Solar System

Topography:

35% continents (high elevation)
65% ocean basins (low elevation)
Very different elevations

Plate Tectonics
Reading: section 5.7

Problem:
South America and Africa fit together like jig-saw puzzle, with matching geological formations and fossils at matching locations
New Idea:
Contents drift (Wegener), now called Plate Tectonics.
Crust broken up into separate, large, plates, which can move around.
Initially rejected by geologists because counter to established ideas, lack of overwhelming evidence, and lack of mechanism to drive drift.
Mechanism to drive drifts -- convection currents in mantle.
Additional Information
Predictions:
Places where continents are moving apart have new crustal material. Places where continents come together have mountain ranges and deep valleys. Motion of continents.

Tests:
Discovery of mid-Atlantic Ocean ridge.

Symmetrical orientation of magnetic field in parallel strips of rock on either side of ridge.

Recently -- laser ranging off of Moon shows motion directly.
Plate Tectonics now the established model.

Surface Evolution

impact craters
plate tectonics
erosion by wind and water, smooths surface

b. Moon
Reading: section 5.4

Highlands
heavily cratered, about 4 billion years old
Maria
lightly cratered, about 3.2-3.9 billion years old
giant impact basins flooded with lava
Dating
radioactive decay of elements in rocks
.
c. Mercury
Reading: section 6.4
Similar Moon
heavily cratered -> old surface
d. Venus
Reading: section 6.5
few impact craters (1000 entire surface) -> young surface -> tectonic activity.
terrain mostly gentle rolling plains.
evidence of volcanism.
e. Mars
Reading: section 6.6
heavily cratered in southern hemisphere
fewer craters, giant volcanoes in northern hemisphere
Conclusion: part of surface young, part old
long rift valley
giant volcano cones
polar ice caps of H_2O and CO_2
dry stream beds, once running water

Surface evolution determined by 3 processes:
(i) impact cratering,
(ii) volcanism and tectonics,
(iii) erosion by wind and water

Summary: Surface Properties

Cratered terrain ubiquitous
cratering due to junk (planetesimals, asteroids, comets) left over from formation of solar system colliding with planets after their formation.
smallest planets (Moon, Mercury) heavily cratered
middle sized planet (Mars) has both heavily cratered and also uncratered regions and extinct volcanos
largest planets (Venus, Earth) have few craters and active volcanos
Why?
More impact craters -> older surface
Rate of cratering declined rapidly after planet formation
Many craters remain where no tectonic (volcanic) activity
Problem:
why do some planets have old surfaces and some young surfaces?
What controls extent of tectonic (volcanic) activity?
Model:
Thickness of rigid crust controls extent of volcanic activity.
Thin crust -> hot rocks from interior break through surface
Thick crust -> hot rocks from interior can't breack through surface.
Next Problem:
what controls thickness of rigid crust?
Model:
Cooling makes rigid crust grow thicker.
(Hotter rocks are more deformable.)
What is source of heating and cooling?

Images:
Mercury Venus Earth Moon Mars ------- ----- ----- ---- ---- Impact Craters BE: BE: BE: BE: BE: 476-478 558,565, 750-753 842,841 1037 (1/2 disk) 570-573, (full disk) (~ maria) 479,485,487 592 891 (detail) (details) 850 (C on C) 492 (2 types) 848 (rays) 493 (rays) AST: AST: AST: AST: AST: 10474, 10488 11557,11558 11593,11629 12059 10511-10515 (full disk) (full disk) 11643 10489 (detail) Volcanoes BE: BE: BE: BE: BE: 560,561 703,704 842 1013 563,564,566 (maria) 852 (detail) AST: AST: AST: AST: AST: 11530 11633 12196 (Olympus) 11634(detail)12463,12600-5 11631,11632 12379-83 (Olymp) 11598,11603 12501 11604,11729 Mountains Comparisons: BE 628 BE: BE: BE: BE: BE: 549,551 647 892-895 (full disk) 555 (rugged) AST: AST: AST: AST: AST: 10651,54 11772 (mud walls) 10549 (scarps) Rocks Surface BE: BE: BE: BE: BE: 527,528 1047-1050 AST: AST: AST: AST: AST: 10779-80 12722-12727 12737-12773 12828-12902 12077,12115 Rivers BE: BE: BE: BE: BE: 657,688 1032,1034 AST: AST: AST: AST: AST: 11480 12121,12482 11326, 11394 12057 Rifts BE: BE: BE: BE: BE: 1013,1065 1043 (detail) AST: AST: AST: AST: AST: 12584,12593 12596,12584 12123,12126 Erosian BE: BE: BE: BE: BE: 1033 AST: AST: AST: AST: AST: Poles BE: BE: BE: BE: BE: 1025 AST: AST: AST: AST: AST: 12461, 12465-8 12571,12554 12503,10388 Topography: BE: BE: BE: BE: BE: AST: AST: AST: AST: AST: 10386 10387 10388 10383-84

2. Interior

Reading: section 5.5, 5.9, 6.7
All planets differentiated:
Layers of different composition and density
densest material sinks to center, lightest float to surface.
For terrestrial planets the layers are:

core (Fe + Ni),
Mercurey and Venus: liquid
Earth: inner solid, outer liquid
Mars: not completely differentiated, rocky material mixed in
mantle (semi-soft dense rocks)
rigid with respect to sudden movements, but flows slowly under steady force.
crust (rigid, light rocks)

Clue is density
density = mass / volume
Density (uncompressed) Water 1 g/cm³ Rock 2 (crust)-5 (densest) g/cm³ Iron Sulfide 5 g/cm³ Iron 8 g/cm³

Structure determined from analysis of Seismic Waves:
p (pressure or sound) waves (can travel through both solid and liquid)
s (shear or side to side) waves (can't propagate through liquid)
propagation speed increases with increasing density.
waves reflect off layers with sudden change in propagation speed, e.g. core-mantle boundary.
Core mantle boundary is bumpy.
More information
http://www.geo.mtu.edu/UPSeis/index.html
http://www.seismo.unr.edu/ftp/pub/louie/class/100/seismic-waves.html
http://lasker.princeton.edu/ScienceProjects/curr/waves/seismic_waves.htm

Density
average density ~ 5.5 g/cm³,
density crust rocks ~2 g/cm³,
densest rocks ~ average density
-> large, high density core must exist.

The Individual Planets

Earth

Moon
low density, all rock, little iron
Mercury
high density, much iron, large core
Earth and Venus
similar, high density, rock mantle, iron core
Mars
medium density, not completely differentiated

Heating and Cooling of the interior

Core Formation
must melt the iron
source of heat?
Heating
1. impacts (originally)
2. splitting of unstable radioactive nuclei
3. sinking of molten iron toward center
(4. Earth: solidification of inner core)
Cooling
convection and conduction to surface
radiation from surface to space
Dependence on Size of Planet
Heating proportional to volume -> proportional to R³
Cooling proportional to surface area -> proportional to R²
Heating/Cooling proportional to Volume/Area proportional to R¹ = size
Smaller planets cool faster and heat less (by impacts and radioactive decay).
-> thicker rigid lithosphere, less volcanism and tectonic activity.
AST 10380 (diagram), 10384 (Earth)

3. Atmosphere

Reading: sections 5.3, 6.8

a. Amount and Composition

Amount of atmosphere determined by balance between production by volcanic outgassing from interior and loss by escape to space and trapping

More massive planet -> stronger gravity -> larger escape velocity, more difficult for gas atoms to escape.

Hotter gas -> faster atoms move, easier to escape.

More massive atoms -> slower they move -> planets lose smallest mass gases first

V_escape=(2GM/R)^1/2,
V_thermal=(2kT/m)^1/2
Escape if V_thermal > V_escape/6

Moon and Mercury - no atmosphere

Ratio atmosphere of Venus:Earth:Mars is 90:1:0.01 (or 1/100)

Composition:

Venus and Mars: mostly carbon dioxide (98%), with some nitrogen (2%). Venus clouds sulfuric acid.
Earth: nitrogen (77%) and oxygen (21%).
Earth and Venus produced similar primordial amounts of atmosphere, because now have similar amounts of nitrogen.

Earth's carbon dioxide dissolved in rain, carried to the oceans, formed into rock. Only nitrogen left. Oxygen due to photosynthesis.

Mars produced less atmosphere and lost some atmosphere to space.

Water:

Water lost on Venus and Mars. Not lost on earth.
photo-dissociated by UV photons from Sun. Hydrogen escapes.
Mars once had running water. Too little atmosphere now for liquid water (vaporizes)

b. Temperature of atmosphere and surface

determined by balance between

heating by absorbing visible Sunlight and
cooling by radiating infrared light to space

F_Sun x A_{disk earth} x fraction absorbed = F_earth x A_earth
(L_Sun/4 pi D²) x pi R² x (1-A) = sigma T⁴ x 4 pi R²

seasons: angle of Sun's light hitting surface

Global circulation -- winds and ocean

north-south circulation carries heat from equator to polar regions
rotation + circulation produces east-west winds

Greenhouse effect:

carbon dioxide and water vapor block escape of infrared light, insulate surface, reduce heat loss, warm surface. Earth warmed 33 C.

Feedback loops:

Water: hotter -> evaporate more water -> increase both insulation and removal of carbon dioxide by rain from atmosphere
Ice: hotter -> melt ice -> reduce reflection of Sunlight -> increase heating
Clouds: (1) Absorb infrared radiation, insulate surface, reduce cooling. (2) Reflect Sunlight, reduce heating. Currently net cooling effect. Hotter -> ??? (biggest uncertainty)

Computer Models

Start from past observations, model past weather, see if agrees with what really happened.
What to include: Atmosphere, Oceans, Sea Ice, Clouds.
Results: getting better
Ocean Temperature

movie (6.2 Mb)
Atmospheric Moisture

movie (4.3 Mb)

see also

NOAA: Global Warming FAQ
Climate Change Fact Sheets (click on Climate Change Information Kit)
Union of Concerned Scientists: Global Warming
National Climate Data Center
World Climate Report
Computer Climate Modeling

Global Warming:
Carbon dioxide has increased 25% in last hundred years. Is increasing at accelerating rate. Increases greenhouse warming.

Ice Ages:
eccentricity of elliptic orbit,
wobble of tilt of Earth's axis,
precession of tilt.
Extinctions: impact -> dust -> atmosphere cooler. 65 million years ago - dinosaurs

Runaway greenhouse effect on Venus

Too warm for water to disolve carbon dioxide,
Too warm for rocks to retain carbon dioxide,
Carbon Dioxide not removed from atmosphere

c. Conditions for a habitable Earthlike planet
if closer -> runaway greenhouse effect (Venus)
if smaller -> less atmosphere, no greenhouse effect -> frozen
if farther -> probably okay near distance of Mars if Earth size, but not smaller

4. Evolutionary stages

Reading: sections 5.9, 6.7
i. formation
ii. heating, differentiation
heavy iron sinks to form core, light silicates form mantle and crust
iii. crust solidification
iv. impact cratering, volcanic flooding, outgassing atmosphere
v. slow evolution - erosion, volcanism, plate tectonics, loss of atmosphere

C. The Jovian Planets

Comparative Planetology - Jovian Planets
Reading: Chapters 7, 8
see also: The Nine Planets and Views of the Solar System
Video Disks: Planetscapes -- Voyager (PV), Infinite Voyage -- (IV)

2. Interiors

Reading: section 7.6
Figs. 7-19,20
Jupiter and Saturn: [AST 10344, PV - 33521]
mostly hydrogen and helium, but differentiated. Giant liquid planets, so they bulge out at the equator.
Core of ice, rocks and iron
Inner envelope of liquid metallic hydrogen
Outer envelope of liquid molecular hydrogen
Gaseous atmosphere
Uranus and Neptune:
core of rocks
icy mantle
liquid molecular hydrogen envelope
gaseous atmosphere
Planets emit more energy than they receive from the Sun.
All have hot cores. Source of heat differs, as the larger volume of Jupiter means it cools more slowly:
Jupiter - gravitational collapse, releases gravitational potential energy. Can't be nuclear fusion like the Sun - not massive enough.
Saturn, Uranus & Neptune - helium settling into core, release gravitational potential energy.
Heat transferred to surface by convection.
No solid surface like the terrestrial planets.

Jupiter

JUPITER and SATURN: AST 10344, PV - 33521 URANUS Magnetic Field: IV - 37:56-38:45
3. Atmospheres

Reading: sections 7.4, 7.5
Composed of hydrogen and helium (primarily) plus methane (CH₄), ammonia (NH₃), and water (H₂0). C,N and O like terrestrial atmospheres, but with hydrogen added to make molecules.
Bands of high velocity east-west winds driven by rapid rotation.
Atmospheres are cold: 40-165K or -300^oF.
Poles and equator are nearly the same temperature.
Giant long lived storm systems. Jupiter's Great Red Spot is 300 yrs old.
Neptune's dark spot.[AST 13291]
But Saturn's bright spot is young.

JUPITER:

   Views       IV - 14:50-15:50
   Rotation:   PV - 32595 (play)
   Winds       PV - 34568 (play)
   Red Spot    PV - 35226, 44923 (red & white + wakes), 35429 (play)

SATURN:

   size        PV - 36090
   Atmosphere  PV - 36103-5, 36120-27, 36147-50
   Red oval    PV - 36162
   Rotation    PV - 36680 (animation)
               PV - 37690 (animation)
URANUS

   size                    PV - 40666
   true-false clr (bands)  PV - 45542
   cloud                   PV - 45538
   cloud motion            PV - 45533

NEPTUNE

   Atmosphere  IV - 44:03 - 47:36

4. Moons and Rings

Reading: Chapter 8

Jupiter's Galilean satellites:

progression from higher density, volcanic Io, to heavily cratered ice and rock Callisto.

Surfaces:

See the Galilean Moons of Jupiter Activity for more images.

Interiors:

All the jovian planets have many moons

different surfaces, compositions, and sizes.

New (small!) moons are still being discovered.

JUPITER:

Io (size)               PV - 35887
    (views)             PV - 35948, 35892-906  (35901 = volcanic crater)
                        PV - 35908-14  (35912 = crater no rim)
    (volcanism)         PV - 35951,60-62) (plumes)
                        PV - 35927-32 (identify volcanoes)
                        BE - 1153-56 (full), 
                        BE - 1158,61,63,64,66,69,70,71 (craters)
                        BE - 1178-83 (plumes)
                        BE - 1246 (internal structure)
Europa (size)           PV - 35850
        (views)         PV - 35856
                        BE - 1216-1218
Ganymede (size)         PV - 35778
         (views)        PV - 35786-89
                        PV - 35792-803
                        PV - 35805-08
                        PV - 44956, 57, 60, 61,76 (high res views)
                        BE - 1220-1223
Callisto (size)         PV - 35734
         (views)        PV - 35742-47
                        BE - 1224-1226

SATURN:

Moons             IV - 27:30-29:25

Mimas (chapt 22)
   size              PV - 39441
   views             PV - 39445-53
                     BE - 1303-5
Enceladus (chapt 23)
   size              PV - 39471
   views             PV - 39474-77
                     BE - 1306
Tethys (chapt 24)
   size              PV - 39489
   views             PV - 39492-99, 39501
                     BE - 1308
Dione (chapt 25)
   size              PV - 39519
   views             PV - 39522-26
Titan (chapt 27)
   size              PV - 39595
   views             PV - 39606-7
                     BE - 1313-16

URANUS:

Titania:
   size                    PV - 41728
   full disk               PV - 45587
   terminator              PV - 45584
   mosaic                  PV - 45645
Arial:
   size                    PV - 41748
   views                   PV - 41762-64
   mosaic                  PV - 45637
   highest resolution      PV - 45608, 45630
Miranda:
   size                    PV - 41769
   full disk               PV - 45653 (color), 45605
                           BE - 1370-76
   mosaic                  PV - 45668
   rugged & grooved        PV - 45611
   fract, grooves, cratrs  PV - 45614
   Theory                  IV - 41:18-43:43

NEPTUNE:

Triton (plumes)         IV - 48:56 - 51:40
                        BE - 1445-51

All the jovians have rings

All the rings are different

Orbit each planet in a very thin disk.

JUPITER:

         
         Jupiter Ring  
         
         
   Ring                    IV - 21:26-21:45
   Ring                    PV - 36084-85
   Rotation:               PV - 32595 (play)

SATURN:

   Rings                   PV - 38029, 31, 46, 51, 96
                           PV - 38575 (animation)
                           PV - 38921 (animation)
   Shepard satellites      PV - 38129-30

URANUS

   Rings:                  PV - 41682-85,89
                           BE - 1356-57
   shepard sattelites      PV - 41619 (same 45528)

NEPTUNE:

   Ring:                   BE 1431-32

D. Formation of the Solar System

Reading: Chapter 4

Difficult problem - few examples

1. Characteristic Properties

Disk Shaped
Two kinds of planets:
Terrestrial - inner, small, density like rock, rocks and iron
Jovian - outer, large, density like water, hydrogen, helium and ices
Common ages of Earth, Moon and meteorites, ~4.6 billion years ago
Asteroids and comets

2. Solar Nebula Theory

Sun formed from contracting interstellar cloud of hydrogen, helium and dust.
Planets formed as part of the process of Sun's formation.

See also: Nine Planets: Origin of the Solar System

3. Formation Scenario

a. Contraction
cloud of gas and dust contracted and flattened into rotating disk.
Planets formed in disk.

Evidence: beta pictoris

Hence, orbits of planets have disk shape.
b. Condensation and Accretion
Grains of solid material grow by condensation - adding one atom at a time from the surrounding gas.
Planetesimals grow by accretion - sticking together in low speed collisions.
Close to Sun hot - only rocks and iron solid -> rocky and metallic terrestrial planets
Far from Sun cold - in addition to rocks and iron, ices of water, carbon dioxide, methane and ammonia also solid -> icy Jovian protoplanets.

Gravity of Jovian proto-planets strong enough to hold solar nebula gases (H & He) -> Jovian planets.
c. Dispersion of Solar Nebula
radiation pressure, solar wind and sweeping up junk by planets (impact craters)
asteriods - remnants of inner rocky, metallic planetesimals
comets - remnants of outer icy planetesimals. Ejected to large distances by Jovian planets gravity

Observations: Extra-Solar planetary systems or mini-binary stars?

Observe Motion of star via Doppler Shift

Unexpected properties

Eccentric Orbits
Jupiter Mass Planets close to Star
Summary

Links to more information

Discovery of Extrasolar Planets

Theories of Planetary Systems

Extrasolar Planets

Extrasolar Planets Encyclopedia

51 Pegasi

Observation of a transit of an extrasolar planet across the face of its star

Formation of the Moon Properties to be explained circular orbit composition similar crust of Earth, but not identical no water Capture Fission Co-formation Giant Impact Video of Giant Impact model: Beyond Earth, chapt 41

E. Life in Other Planetary Systems

1. Possibility of Life in Other Solar Systems Usually assume that it will be like us or we won't recognize it (and vice-versa) How many stars like ours in our Galaxy? Textbook Appendix shows 4/33 or about 0.12 are similar - Alpha Centauri, Tau Ceti, Procyon A and the Sun itself There are about 400 billion stars in our Galaxy Stars formed on the average of about 10 per year Are there other planetary systems? We see other solar nebulae Other planetary systems have been found - about 6/100 stars searched over the last 10-15 years Is life likely to arise? Life on Mars? Mini-fossils of bacterium 3.5-billion years old within meteorite found on Earth? NASA Summary with links to orginal article and rebuttles We have found amino acids and PAHs (carbon-based molecules associated with simple life in meteorites and between the stars in the dust and gas clouds. Life on earth - simple one-celled organisms - seemed to appear as soon as the surface was cool enough. Can we actually visit each other? Using current technology, it would take 40,000 years for us to travel 4 light-years to the nearest star. This would be extremely expensive. Far more likely to exchange information at a distance. Would the scientists tell us if they make contact? Yes, any signal would be immediately confirmed by another telescope (usually in another country) and if confirmed publicly announced. SETI Institute is a non-profit doing projects to Search for Extra-Terrestrial Intelligence.

2. Estimating (calculating) the number of technological civilizations we could contact:

N = p R_* L

N = the number of advanced civilizations in our galaxy, the Milky Way. [no units]

R_* = the rate of star formation in the Galaxy, usually taken to be 10 stars per year. [per year]
L = the average lifetime a civilization remains technologically active.[year]

p = A number [no units] between 0 and 1. It's the product of a number of factors explained below.

The product p = f_pn_ef_lf_if_e and each of these factors is the average:
f_p = fraction of stars which have planets.
n_e = Earthlike planets per Solar System.
f_l = Earthlike planets which have developed life.
f_i = fraction of life-bearing planets which have developed intelligent life.
f_e = fraction of intelligence-bearing planets capable of interstellar communication.

Links to other Solar System resources

The Nine Planets Views of the Solar System Jet Propulsion Laboratory Picture Archive NASA Photo Gallery Planetary Geology Course by Joseph C. Cain, Florida State University

This page has been accessed times.

This page will be updated continually throughout the course.
Updated: 2004.01.11 (Sunday) 23:29:52 EST

Visions of the Universe

Bob Stein's home page, email: steinr@pilot.msu.edu

ISP 205, Section 3, Spring 2003, Prof. Stein UNIT II: THE PLANETS OUTLINE