Download Week 9

Chapter 7
Our Planetary System
7.1 Studying the Solar System
• Our goals for learning
– What does the solar system look like?
– How has it evolved over time?
– What are the major features of the Sun and
planets?
– What patterns can we find?
– Can we begin to create an organized science of
the planets?
Earth, as viewed by the Voyager spacecraft
Actually
Fig. 7.1
cartoon
Voyager
“family portrait”
Image from 1999
What does the solar system
look like?
Planetary Science
Looking “down”
• We’re looking for patterns
– 1 thermonuclear object
– Eight major planets with
nearly circular orbits
moving counterclockwise.
– Most of what we see is in a
single plane extending
outward from the Sun’s
equator (the ecliptic)
– Thousands (millions?) of
minor objects, like Pluto,
which are smaller and
mostly located in the outer
solar system.
•
•
Old term is “comparative planetology”
Rationale used to be “we can learn more about
Earth by studying other worlds in the solar
system”.
Now: Simply understanding planetary processes
Focus on processes yields generalized
knowledge of worlds
•
•

Instead of memorizing facts about a particular world.
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Scaling
Exercise
Localized Scaling Exercise
For ASU, the Sun
to Neptune distance
equals from here to
the student union
grapefruit-sized
See pages 8-10 in Chapter 1
The mass of the entire
Solar System would fit in
a large soda cup.
That soda cup in
the middle weighs
almost as much as
the real (unscaled)
Moon!
The remainder is
scattered across an
area roughly the
size of the entire
campus.
We are here…
Week 9
• Tour of Chapter 7: Planetary
Overview
• Chapter 8: Formation of the
Solar System
Localized Scaling Exercise
Life Cycles
• The Solar System as we see today is the last
frame of a long movie
• How did it get to this point?
Life Cycles
• We can say with certainty that we
are looking at a butterfly
• Because we have seen the caterpillar and the pupae
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Scale Model of Sizes
traditional planets
Scale Model of Sizes
All large objects
Scale Model of Sizes
Sun and traditional planets
Scale Model of distances
NOTE: logarithmic scale in AU
http://en.wikipedia.org/wiki/Graphical_timeline_of_our_universe
Sun
• Over 99.9% of solar system’s mass
• Made mostly of H/He gas (plasma)
• Converts 4 million tons of mass into energy each second
Mercury
• Made of metal and rock; very large iron core
• Desolate, cratered; long, tall, steep cliffs
• Very hot and very cold: 425°C (day), –170°C (night)
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Venus
Earth
Earth and Moon
to size scale
• Nearly identical to Earth: Size, Composition, Density
• Surface hidden by CO2 clouds with acid rain.
• Runaway greenhouse effect:
 Hotter than Mercury: 470°C, day and night
• Only surface liquid in the Solar System
• Liquid metal core with rocky surface
• Proportionately large moon – a true binary planet
Jupiter
Mars
• Nearest gas giant
• Mostly H/He; no solid
surface
• Density increases with
depth. May have a
terrestrial core
• Many moons, rings…
• Appears Earth-like, but only 6 millibars surface pressure
• Small frozen metal core with rocky surface.
• Giant volcanoes and canyon. Polar caps, seasons, etc.
• Evidence of flowing water
Jupiter’s moons
interesting as
planets in
themselves,
especially the
four Galilean
moons
• Io (shown here): Active sulfur volcanoes all over
• Europa: Confirmed liquid ocean under surface ice crust
• Ganymede: Largest moon in solar system
• Callisto: Cratered ice ball
– Mini-solar system
• May be most common
type of planet
Saturn
•
•
•
•
Gas giant like Jupiter (H & He). Density < Water.
Most prominent rings
Moons include Titan w/ 1.5 bar surface atmosphere
Cassini spacecraft currently mapping the system
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Uranus
Neptune
• Smaller than
Jupiter/Saturn;
but still much
larger than Earth
• Made of H/He
gas & hydrogen
compounds (H2O,
NH3, CH4)
• Rotates on side
• Moons and rings
also tilted!
• Another mediumsized gas giant
• Similar chemistry
to Uranus
• Most distant major
planet
• Likely host to a
captured KBO in
the moon Triton
Pluto
•
•
•
•
Newly designated type for Minor Planets
Ice and rock (comet-like) composition w/ 3 moons
Large moon Charon similar in size – binary system
New Horizons mission arrives in 2016 (13 miles/second)
What are the most common
patterns of the Sun and planets?
7.2 Patterns in the Solar
System
• Our goals for learning
– What features of the solar system provide clues
to how it formed?
– All orbit in the same direction
– Obey Kepler’s 3rd Law
– Angular Momentum conserved
– All created at the same time
Sun and planets to scale
5
What features of the solar system
provide clues to how it formed?
Motion of Large Bodies
• All large bodies
in the solar
system orbit in
the same
direction and in
nearly the same
plane
• Most also rotate
in that direction
Two Primary Planet Types
Swarms of Smaller Bodies
• Many rocky asteroids,
rocky-ice Kuiper Belt
Objects (KBOs) and
i comets populate
icy
l
the solar system
• Terrestrial planets are
rocky, relatively small,
andd close
l
to
t the
th Sun
S
• Jovian planets are
gaseous, larger, and
farther from Sun
Rosetta Stones
7.3 Robotic Exploration
• Entire Uranian system
(planet, rings
(p
g &
moons) are all knocked
on their sides
• Likely from a
megaimpact before the
planetesimal period
• Venus flipped almost
180°
• Census
• Description
• Explanation
• Understanding
• Hardware:
Flybys
Orbiters
Landers/Probes
Sample
Returns
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Stepping out
Flybys
• Technically
simplest way to
get close up. Flys
past planet just
once
• Cheaper than other
mission types but
have less time to
gather data
• First lunar flyby in
1959
Pre-1970’s: Planets were astronomical objects
Post-1970’s: Planets have become geologic objects
The Golden Age of Planetary Exploration is right now
Census, Description, Explanation & Understanding
Orbiters
• Go into orbit around
another world (Moon,
1966)
• Full planetary coverage
• More time to gather data
but limited high resolution
data about world’s
surface.
– Still hundreds of miles
away
• Spectroscopy techniques
perfected
Sample Return Missions
• Gather samples from another body,
return them to Earth
• Apollo/Luna missions (Moon), and
Stardust (Comet P/Wild 2) are only
sample
l return missions
i i
to date
d
• Mars sample return likely next…
Biologically dangerous?
Perhaps redundant
Probes or Landers
• Initially “impact”
impact landers (1962)
– Suicide missions but got real close early on
• Land on surface of another world (Venus,
1965)
• Goal to explore surface in detail
– Mars, 1997-present
– Titan, 2006
– Asteroids, 2004-present
Current Status
• Spirit and Opportunity rovers active on
surface of Mars. Global Surveyor in orbit
• Cassini orbiter at Saturn
• Messenger at Mercury
• New Horizons in route to Kuiper Belt
• Ulysses solar polar mission is out of the
plane of the solar system
• Both Voyagers headed for interstellar space
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Where are the Voyagers?
Chapter 8: How did it form?
1. Any credible theory of solar system formation
must explain…
2. Patterns of motion of the large bodies
•
Orbit in same direction and plane
3. Existence of two types of planets
•
Terrestrial and jovian
4. Existence of smaller bodies
Launched in 1977,
may cross heliopause
in 2008
•
Asteroids, comets, Kuiper Belt objects
5. Notable exceptions to usual patterns
•
Rotation of Uranus, Earth’s moon, etc.
Overlay of Oort Cloud of comets @ 1 to 10 Billion
What theory best explains the
features of our solar system?
•
The nebular theory states that our solar system
formed from the gravitational collapse of a giant
interstellar gas cloud—the solar nebula
(Nebula is the Latin word for cloud)
•
•
•
Kant and Laplace proposed the nebular
hypothesis over two centuries ago
A large amount of evidence now supports this
idea…especially some Hubble images
Older references will still discuss the
planetesimal or close encounter theory.
Review 1
• Gravity
– Mass will be attracted to other masses
proportionally to the masses involved
– Mass
M will
ill concentrate
t t in
i areas off greatest
t t
gravitational attraction (usually the
center of mass)
– Sun’s gravity acts
throughout the
solar system
8.2 The Birth of the Solar System
• Our goals for learning
– A review of basic physical principles
– Where did the solar system come from?
– What caused the orderly patterns of
motion in our solar system?
Review 2
• Density
–Mass per unit volume
–For
For a given composition
composition, density
increases directly with mass
–Phases Changes are
reflections of density
Gases ↔ Liquids ↔ Solids
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Review 3
Review 4
• Temperature
– A measure of molecular motion

Absolute Zero = temperature at which all molecular motion stops
• Pressure
– A measure of force per unit area
Heated molecules
•Pressure changes
most readily in a
gas, least so in a
solid.
• Phases are directly
related to temperature:
Solids = frozen liquids
Liquids = condensed gas
 Gases = free clouds of
atoms or molecules


Review 5
• Temperature & Pressure
– Changing temperature changes pressure
Review 6
• OK, maybe this isn’t a review, but…
• Phase Diagrams
• Phase
Ph
Diagrams
Di
show where and
how phase changes
occur
• Every natural
material has a
phase diagram
• Triple Point
• Critical point
• Increasing pressure
in a gas
(compressing)
causes it to heat up.
• Releasing pressure
in a gas causes it to
cool down.
Review 7
• Chaos Theory
– Self-organization
– Phase changes are an
example
p of self-organization
g
– The stability of an
equilibrium distribution is a
consequence of the fact that
individual events are random
and independent of other
events. Individual chaos
therefore implies collective
determinism.
-Heinz Pagels
move faster  more force
Where did the solar system
come from?
Cosmos animation
of solar system
formation
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Galactic Recycling
Evidence from Hubble
• Elements that
form planets were
made in 1st
generation stars
and then recycled
through
interstellar space
to form 2nd
generation stars
& their planets
• We can see stars
forming in other
interstellar gas
clouds, lending
support to the
nebular theory
Examples of proplyds
(Protoplanetary disks)
in Orion
Flattening
Conservation of Angular Momentum
• Rotation speed of
the cloud from
which our solar
system formed
f
d
must have
increased as the
cloud contracted
• Starting with a hemispherical cloud: Random
collisions between particles will eventually form
a disk with a random orientation.
Slightly dominant
direction vector will
take up angular
momentum which is
conserved into the
present day.
Disks around other Stars
“Circular” Orbits
• Form because they
survive.
• Collisions between
gas andd dust
d
particles in cloud
reduce random
motions.
• Particles NOT on
collision courses
survive.
•
Observations of disks around other stars
support the nebular hypothesis
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What have we applied?
8.3 Formation of Planets
• Solar System Formation?
– Galactic recycling built the elements from which
planets formed.
– We can observe stars forming in other gas clouds.
• Orderly patterns of motion?
– Solar nebula spun faster as it contracted because of
conservation of angular momentum
– Collisions between gas & dust particles caused the
nebula to flatten into a disk
– We have observed such disks around newly forming
stars
Why are there different types of planet?
• Our goals for learning
– Why are there different types of planets?
– How
H did terrestrial
t
t i l planets
l t form?
f
?
– How did jovian planets form?
– What ended the era of planet formation?
Coalescence of particles
Numerous small particles build big ones
In-falling volatiles sublimated….ergo, The Frost Line
Inner parts of
disk are hotter
than outer parts.
Rock can be
solid at much
higher
temperatures
than ice.
The Frost Line
Fig 99.5
5
Inside the frost line: Too hot for hydrogen compounds to form ices.
Outside the frost line: Cold enough for ices (CH4 or NH3) to form.
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How did terrestrial planets form?
•
•
•
Small particles of rock and metal were
present inside the frost line
Pl t i l off rockk andd metal
Planetesimals
t l built
b ilt up
as these particles collided
Gravity eventually assembled these
planetesimals into terrestrial planets
Accretion of Planetesimals
•
•
Many smaller objects collected into just a
few large ones = accretion
Individual planets differentiated into layers
with densest materials at core
•Small particles
of rock and
metal present
inside the frost
line
•Planetesimals of
rock and metal
built up as these
particles collided
•T-tauri stage
blows volatiles
out of inner solar
system.
•Gravity accretes
planetesimals
into terrestrial
planets
How did jovian planets form?
• Ice crystals forms small particles
outside the frost line.
• Larger planetesimals and planets form
by sweeping out larger area of orbit.
• Metal particles form cores of gas giants
• Gravity of these larger planets was able
to draw in surrounding H and He gases.
Going
Jovian
Gravity of rock
and ice in jovian
region draws in
H and He gases
Moons of jovian planets form in miniature disks
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Onset of
Solar
Wind
Outflowing
O
tflo ing
matter from
the Sun -- the
solar wind -blew away
the leftover
gases
Solar Rotation
• In nebular theory,
young Sun was
spinning
p
g much faster
than now
• Friction between solar
magnetic field and
solar nebular slowed
rotation over time
Summary
• Why multiple types of planets?
– Ices sublimate inside the frost line
– Gases blown out by solar wind
– Rock, metals, and ices/gases condensed outside the
frost line
• How
H did the
h terrestrial
i l planets
l
form?
f
?
– Rock and metals collected into planetesimals
– Planetesimals then accreted into planets
– Planets differentiated into core, mantle, crust
• How did the jovian planets form?
– Additional supply of ice particles and gases outside
frost line made planets there more massive
– Gravity of these massive planets drew in H, He gases
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