Earth, Moon and Mars: How They Work

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Earth, Moon and Mars How They Work
Professor Michael Wysession Department of Earth
and Planetary Sciences Washington University, St.
Louis, MO Lecture 9 Solar System
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Eagle Nebula
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Eagle Nebula - Star birth clouds. UV radiation
from nearby hot stars is eroding and condensing
clouds of cool hydrogen gas that is an incubator
for new stars
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Helix Nebula cometary knots
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Collapse in 100,000 yrs 15,000 AU cloud to
1-AU-thick solar nebula Temperatures were gt500C
in inner solar system
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Carbonaceous chondrites Primitive
planetesimals Ordinary chondrites (Types
3-6) Metamorphosed planetesimals
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Iron meteorites Core of differentiated
planetesimals Achondrites (Howardites,
Eucrites, Diogenites) Crust of differentiated
planetesimals
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Different temperatures in the protoplanetary disk
with distance from the sun --gt determined history
of planetary formation
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Gas, water, volatiles driven out to snow line
at about 5 AU -- depleted in inner nebula Likely
associated with T-Tauri phase of Sun Allowed
rapid (10,000 yr) runaway growth of 10-20
Earth-mass core allowing capture of gas before
nebula dispersed --gt Jupiter Cores of Saturn,
Uranus, Neptune likely formed in the same region,
gravitationally dispersed by Jupiter Inner
planets formed later, from mostly dry refractory
materials Water now on EarthMars a combination
of initial water and water accreted later by
drift back of icy planetesimals or comets flung
from region of Jupiter (early Earth was wet) Late
Heavy Bombardment Jupiter/Saturn in 2-1
resonance (Neptune flung out into outer solar
system)
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• Sources for heat of early terrestrial planets
• Impacts of planetesimals
• 2. Gravitational collapse
• 3. Compression
• 4. Radioactive decay of short-lived isotopes
• 5. Collapse of iron core
• 6. (For Earth) Impact of proto-moon

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Sun is 99.85 of mass of the Solar System
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Suns magnetic polarity flips regularly with
22-year cycle. Magnetic field is concentrated by
1000x in center of sunspots. Suns luminosity
has increased by 30 since its birth --- now
grows by 1 every 100 Myr. May cause a runaway
Greenhouse on Earth in 500 Myr that will
extinguish multicellular life.
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Solar Flares
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Comparison of Terrestrial Planets
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MERCURY Mass 5.5 of E Density 98.4 of E R
2440 km R(core) 1800 km g 37.8 of E
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Mercury Mariner 10, MESSENER
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Liquid outer core generates magnetic field
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Surface T 80K to 700K
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Trace water amounts may survive in
permanently-shadowed craters
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• Evidence of volcanism
• low-Fe basaltic shield volcano, 100-km across
• Shows evidence of slight exosphere (Mg, Ca, Na)

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Plentiful scarps suggest planetary contraction
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Caloris Basin Bigger according to Messenger
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Caloris antipode suggests focusing of seismic
waves
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VENUS Mass 81.5 of E Density 95.1 of E R
6052 km (95 of E) g 90.5 of E
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No rotation - no magnetic field No water - no
asthenosphere - no plate tectonics Atmosphere -
92 bars 96.5 CO2 (?Life in Atmosphere?) Mean T
464ºC
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10,000s of shield volcanoes only 1000 craters
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Venera Blocky plate-like rocks and soils
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Coronae Related to upwelling? Evidence of mantle
plumes?
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Tessera Continental composition? Predate
volcanic plains?
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Dynamic history ? Catastrophic resurfacing
ended rapidly quiet since? ? Episodic plate
tectonics punctuated by one-plate dynamics and
quiet periods (like now)? ? One-plate dynamics
with periodic overturns due to gravitational
instability? ? Transition from plate-tectonic
mobile-lid regime to quiet stagnant-lid
regime? (Earths future?)
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Gas/Ice Giants
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JUPITER Period 11.86 yrs SATURN Period
29.46 yrs However, at some point in a 21
resonance Destabilized solar system Late
Heavy Bombardment
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Aurora on Jupter Bright spots are magnetic flux
tubes, connecting with moons Io, Europa, and
Ganymede
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Red Spot 23,000 km-long hurricane (at least 180
yrs old)
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Io, Europa, Ganymede in 421 resonance of orbits
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Io 100s of volcanoes active at any time Lava is
both basalt and sulfur Orbital resonance of moons
causes their orbits to greatly fluctuate --gt
large tidal stresses Boosaule Mons 16.7 km high
non-volcanic mountain
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Europa Liquid ocean gt150 km thick Very few
impacts suggests that the crust is young and
constantly reworked
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Fractures form arcs in response to Jupiters
tidal stresses suggests icy crust is thin
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Saturn eclipsing the sun (Cassini)
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Saturns hexagonal pattern at north pole
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Swirling hurricane-like vortex at Saturns south
pole (Cassini)
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Lightning on Saturn (2-hour storm Cassini)
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Aurora, Saturns south pole (Cassini)
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Storms on Saturn (winds gt 360 km/hr Cassini)
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Cassinis voyage to Saturns moon Titan.
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Titan
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Titan only moon with a substantial atmosphere
(nitrogen)
Liquid methane on a water-ice surface?
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A 360-deg panoramic view of the terrain around
Huygens' landing site. The white streaks might be
a ground 'fog' of methane or ethane vapor. The
temperature of the landing site itself was minus
291 degrees F. The soil has the consistency of
wet sand or clay and is covered by a thin crust
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From an altitude of 16 km, Huygens photographed
these drainage channels leading to a shoreline.
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Lakes (liquid methane/ethane) at Titans north
pole (Cassini)
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Titans equatorial winds blow the wrong
direction, based on Titans dunes
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Enceladus caught in gravitational resonance with
larger Dione large orbit swings cause large
tidal heating and ice geysers
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Enceladus Surface Temperature Internal Hot Spot
at South Pole? (Cassini)
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Enceladus Surface Temperature Internal heat
leaking out of fissures? (Cassini)
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Iapetus Landslide along 15-km-high scarp
(Cassini)
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ICY GIANTS
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Neptune's moon Triton - so cold (minus -391?F)
its surface contains frozen nitrogen. Largest
moon to orbit in a retrograde direction.
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Kuiper Belt Objects (green) Centaurs
(orange) Trojans of Jupiter (pink)
Outer Solar System Objects
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Spike at 40 AU are Plutinos (including Pluto with
23 resonance with Neptune
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KBO evolution and the Nice Model
KBOs before the Jupiter/Saturn 21 resonance
Scattering of KBOs into inner solar system after
shift of Neptune
After ejection of KBOs by Jupiter
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Inner Solar System Bodies
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Asteroids
Eros The solar systems snow line could have
been close to Mars, so many asteroids are
probably icy
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ASTEROIDS (Itokawa)
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• Oort Cloud
• 2000 - 50,000 AU
• trillions of comets gt 1.3 km
• total mass may be 5 Earth masses

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Comet West
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Comets
and Deep Impacts collision with Comet Tempel 1
showed that comets can be more like asteroids
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Solar coronal mass ejection ripping tail off of
coment Enke (STEREO)