Chapters 16-19 in Seeds:
Solar System Overview (for exam):
General properties of the planets
Order, relative size, make-up (terrestrial vs. Jovian), atmosphere (including greenhouse effect)
General properties of the interesting moons and ring systems (e.g., origin of our moon, Galilean Moons, Titan)
Extrasolar planets (how many, how detected?)
Comets, meteors, asteroids
Where do they come from, what are they made of, origin of meteor showers
Very basic stuff, most can be memorized, nothing too complex – basically what’s here in the slides

Chapter 16: Origin of the Solar System
Solar Nebula Hypothesis
Context for Understanding Solar System
Extrasolar Planets
Dust Disks, Doppler Shifts, Transits and Eclipses
Survey of the Solar System
Terrestrial Planets
Jovian Planets
Other “Stuff” including apparent patterns with application to the nebular hypothesis

Patterns in Motion
All planets orbit in almost the same plane (ecliptic, AKA Zodiac)
Almost all motion is counterclockwise as seen from the north:
All planets orbit in this direction
*Almost* all planets spin in same direction
with axes more-or-less perpendicular to ecliptic
Regular moons (like our own moon) orbit in this direction, too
Planets are regularly spaced
steps increasing as we go outward

Solar Nebula Model
Planets form from disk of gas surrounding the young sun
Disk formation expected given angular momentum in collapsing cloud
Naturally explains the regular (counterclockwise) motion
Makes additional explicit predictions
Should expect planets as a regular part of the star formation process
Should see trends in composition with distance from sun
Should see “fossil” evidence of early steps of planet formation

Extra-Solar Planets
Hard to see faint planet right next to very bright star
Two indirect techniques available
(Like a binary star system but where 2nd “star” has extremely low mass)
Watch for Doppler “wobble” in position/spectrum of star
Watch for “transit” of planet which slightly dims light from star
About 100 planets discovered since 1996   See http://exoplanets.org/
Tend to be big (³Jupiter) and very close to star    (easier to see)

Characteristics of “Planets”
Two types of planets
Terrestrial Planets: small, rocky material: inner solar system
Jovian Planets: large, H, He gas outer solar system
Small left-over material
provides “fossil” record of early conditions
Asteroids     mostly between orbits of Mars and Jupiter
Comets     mostly in outermost part of solar system
Meteorites –  material which falls to earth

Slide 7

Evidence of Assembly Process?    Craters

Craters evident on almost all small “planets”

Chapter 17: Terrestrial Planets
Earth
History, Interior, Crust, Atmosphere
The Moon
In particular origin
Mercury
Venus
Mars
Including water (and life ?)

“Comparative Planetology”
Basis for comparisons is Earth
Properties of Earth
Similarities and differences with Mars and Venus help us understand Earth better (e.g., life, greenhouse effect, etc.)
Won’t spend class time on basic properties (size, gravity, orbital period, length of day, number of moons, etc.) but you should have some relative ideas about these (see “Data Files” in text).

Timeline

Earth’s Atmosphere: Greenhouse Effect

The Moon and Mercury
No atmosphere
Cratering is evidence of final planet assembly – lots to be learned from craters

Examples of craters on the moon
Images on line at
The Lunar and Planetary Institute:
http://www.lpi.usra.edu/expmoon/lunar_missions.html
Detailed record of Apollo work at:
http://www.hq.nasa.gov/office/pao/History/alsj/frame.html

Effects of late impacts

Moon: Giant Impact Hypothesis
Explains lack of large iron core
Explains lack of “volatile” elements
Explains why moon looks a lot like earth’s mantle, minus the volatiles
Explains large angular momentum in the earth-moon system

Venus

Expect Venus to be similar to Earth?
(It isn’t!)
Venus only slightly closer to sun, so expect about same initial composition
Venus only slightly smaller than Earth, so expect about same heat flow
Venus atmosphere is dramatically different
Very thick CO2 atmosphere
Virtually no water in atmosphere or on surface
Venus shows relatively recent volcanic activity, but no plate tectonics
Both probably related to its slightly closer position to the sun
which caused loss of its critical water
Thick atmosphere and clouds block direct view so information from:
Orbiting radar missions  (Magellan in early 90’s)
Russian landers (as in previous photo)

Surface Relief of Venus from Radar
Venus does show evidence of “recent” volcanism
It does not show linear ridges, trenches, or rigid plates
In a few spots there are weak hints of this – but clearly different

Volcanoes
Sapas Mons
Lava flows from central vents
Flank eruptions
Summit caldera
Size:
250 miles diameter
1 mile high

Lava Channels
Large!
100’s of miles long
1.2 miles wide
High Venus temperatures may allow very long flows
Composition could also be different

Slide 23

Lots of Martian Science Fiction
Best, most recent and scientifically accurate is probably Kim Stanley Robinson’s series:
Red Mars, Blue Mars, Green Mars
Terraforming/colonization of Mars

Mars and the Pattern of Geologic Activity
and Atmospheric Loss
Expect intermediate geologic activity based on size
RMars = 0.53 REarth         RMoon = 0.27 REarth
Earth still active but lunar mare volcanism ended ~3 billion years ago
Expect intermediate atmospheric loss
Smaller size will make atmospheric escape easier
Cooler temperature (farther from sun) will make astmospheric escape harder
In some ways Mars is most “Earth-like” planet
Has polar caps
Has weather patterns
Had (in past) running water
May have had conditions necessary for development of life

Which planets can retain which gasses?

Mars atmosphere today
Pressure is only ~1% of Earth’s
Composition:  95% CO2    3% N2    2% Ar
Water:
Pressure too low for liquid water to exist
Water goes directly from solid phase to gas phase
CO2 (dry ice) acts like this even at terrestrial atmospheric pressure
Water seen in atmosphere
Water seen in polar caps
Evidence of running water in past
Carbon dioxide (CO2)
Gets cold enough for even this to freeze at polar caps
Unusual meteorology, as atmosphere moves from one pole to other each “year”

Mars dust storm

Sand Dunes on Mars
Spacecraft in Mars orbit
Mars Global Explorer
Mars Odyssey
Even though atmosphere is thin, high winds can create dust storms

Water ice clouds

Ancient River Channels?
(note channels older than some craters – by superposition)

Recent liquid water?
(water seeping out of underground “aquifer” ?)

Layered Deposits

Chapter 18: Worlds of the Outer Solar System
Jupiter
Condensation model
Atmospheric winds
Atmospheric chemistry
Magnetic fields
Other Jovian Planets (Saturn, Uranus, Neptune)
will only cover major differences from Jupiter
Satellites (i.e. Moons)

Jovian Planets

Ice+Rock Core    H+He “Atmosphere”

Jupiter as seen by Cassini

Aurora on Jupiter

Comparison of Jovian Planets
Variation in distance presumably ultimate causes other effects
P:      Kepler’s third law
T:      Falloff mostly just result of falling solar energy
But Neptune hotter because more internal heat
M:     Clue to details of solar nebula mode
Less material in outer solar system – or perhaps less efficient capture
r:      Should drop with mass because less compression
Works for Saturn vs. Jupiter
Increase for Uranus, Neptune indicates less H, He and more heavy material

Saturn as seen by the Hubble Space Telescope

Rings are individual particles all orbiting separately
Each particle – dust to golf ball to boulder size –
is really a separate moon on its own orbit
Orbit with Keplerian velocities:  high in close, slow farther out
Nearby relative velocities are low – so particles just gently bump into each other – slowly grinding themselves up
Structure in rings largely caused by gravity of moons

Comparison of Rings
All within Roche limit
Details controlled by Resonances and Shepard Satellites

Jupiter as a miniature solar system
Four large moons (Io, Europa, Ganymede, Callisto)
Regular (equatorial, circular) orbits
Pattern of changing density and composition with distance
Inner two (Io, Europa) mostly rocky, volcanic activity
Outer two (Ganymede, Callisto) more icy

Io, Europa break rules about activity
Io most volcanically active body in solar system
Europa shows new icy surface with few craters

Tidal heating explains activity
Large tides from Jupiter flex satellites
Friction from flexing heats interiors
Important for Io, Europa, some other outer solar system satellites

Possible H2O ocean on Europa
Tidal heating may keep H2O liquid under ice cover
Perhaps a location where life could evolve
“Europa Orbiter” Mission being planned to determine if ocean exists

Comparison of Satellites

Titan
Largest moon of Saturn
Has thick atmosphere
Pressure ~ 1 earth atmosphere
Mostly N2, some CH4
Gas held because of low T
UV acting on CH4 Þ smog
Ethane produced – Lakes?
Can “see” surface only in IR
Cassini dropped a probe in early 2005.
“Code of the Lifemaker” by James P. Hogan, good sf

Ch. 19:  Meteorites, Asteroids, Comets
Small bodies are not geologically active
They provide “fossil” record of early solar system
Asteroids
Mostly from region between Mars and Jupiter
Left over small debris from accretion, never assembled into a large planet
Meteorites come mostly from asteroids
Comets
“Stored” on large elliptical orbits beyond planets
Thought to be “planetesimals” from Jovian planet region, almost ejected from solar system in its early history
Meteorites provide only samples besides Apollo
With sample in hand, can perform very detailed analysis:  detailed chemistry; radioisotope age; other isotope info

Asteroids
Most located between Mars and Jupiter
Largest is Ceres
1/3 diameter of moon
Most much smaller
>8,000 known
Total mass << Earth
A few make it to earth
source of the meteorites

The larger asteroids

Phobos & Deimos:  Two “misplaced” asteroids?
Phobos and Diemos are small (~25 km and ~15 km diam.) moons of Mars
Look like captured asteroids rather than moons formed in place
Are “C” class – i.e. dark “Carbonaceous” type “asteroids”

Types of Meteorites
Three main kinds of meteorites
Carbonaceous chondrites: Most primitive material – dark because of C
Stones Similar to igneous rocks
Irons Metallic iron – with peculiarities

Meteors vs. Meteorites
Meteor is seen as streak in sky
Meteorite is a rock on the ground
Meteoroid is a rock in space
Meteor showers (related to comet orbits) rarely produce meteorites
Apparently most comet debris is small and doesn’t survive reentry
Meteorites can be “finds” or “falls”
For a fall – descent actually observed and sometimes orbit computed
Most have orbits with aphelion in asteroid belt

Large Meteor over the Tetons (1972)

The Leonids  2001
APOD site:  Picture by Chen Huang-Ming

Meteor Showers and Comets
Meteor showers caused by large amount of small debris spread out along comet orbits
Almost none makes it to the ground – no meteorites
Occur each year as earth passes through orbit of comet
Appears to come from “radiant point” in sky
Leonids:  Mid November

Comets:         Hale-Bopp in April 1997

Hale-Bopp clearly shows components

Comet characteristics
Most on long elliptical orbits
Short period comets – go to outer solar system
“Jupiter family” still ~ in plane of ecliptic
“Halley family” are highly inclined to ecliptic
Longer period ones go out thousands of AU
Most of these are highly inclined to ecliptic
Become active only in inner solar system
Made of volatile ices and dust
Sun heats and vaporizes ice, releasing dust
“Dirty snowball” model

Importance of comets
Evidence of solar nebula
Source of H2O and CO2 for earth
Impacts continue
Impacts on Earth
Extinction of the dinosaurs
SL-9 impact on Jupiter

Pluto and Charon