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Announcements
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Assignments were very good this week!
Let me know this week if you’re planning to do a
presentation rather than a report
The Search
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An overview of the Mars Rover Mission
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Gas Giant Planets
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Sketch of a Gas Giant
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Who's who in the Outer Solar System
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Formation of Gas Giants
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Formation of GG moons
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Tidal Forces
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Visits to the Planets
How Unique is Earth?
The Mars Rovers
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Identical pairs of rovers sent to opposite
sides of Mars
Spirit and Opportunity
Each has a 12:20 `day' (sol) ; since on
opposite sides of Mars, it is always day
for one of the two
Primarily geology mission.
The Mars Rovers
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Launched in June/July 2003
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3 Stages:
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Get off out Earth's surface
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Get out out Earth's orbit
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Head towards Mars
The Mars Rovers
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Began landing in Jan 2004
Entered atmosphere at 12,000 mph
(Chicago -> San Francisco in 9 minutes)
Broke using heat shield, parachute.
Took pictures on decent to gauge
horizontal velocity
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Deployed airbags
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Fired retro-rockets
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Bounced a lot
The Mars Rovers
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Once landed and stable, base unfurled
Rover, which was also folded up,
unfurled
The Mars Rovers
The Mars Rovers
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Four Science Goals:
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Determine whether Life ever arose
on Mars
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Characterize the Climate of Mars
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Characterize the Geology of Mars
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Prepare for Human Exploration
The Mars Rovers
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Search, characterize rocks & soils that hold clues to
past water activity and geologic process
Determine distribution, composition of minerals,
rocks, and soils surrounding the landing sites.
Perform "ground truth" of surface observations made
by orbiters
Search for iron-containing minerals that indicate water
Geological clues to the environmental conditions
that existed when liquid water was present. Assess
whether those environments were conducive to life.
The Mars Rovers
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Cameras
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Panoramic Camera (Pancam)
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Microscopic Imager (MI)
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Engineering cameras: Hazcams and Navcams
Spectrometers
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Miniature Thermal Emission Spectrometer
(Mini-TES)
Mössbauer Spectrometer (MB)
Alpha Particle X-Ray Spectrometer (APXS)
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Rock Abrasion Tool (RAT)
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Magnet Array
Gas Giant Planets
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Overview
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Who's Who
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Formation
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Moons
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Tidal Forces
Our Solar System
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Almost all of mass of planets are in the 4 giant
planets
The Giants
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The Giants are sometimes all
called `Jovian' planets after
Jupiter
After more exploration
showed their diversity, this
term lost favor
The Giants
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The giant planets inhabit the
outer solar system (5-30 AU)
This means they get less
energy from the Sun (4% 0.1%) per area
Top of cloud cover of planets
is very cold (-170oF --350oF)
The Giants
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The giant planets can be
weighed very accurately by
measuring the speed of their
moons.
Much heavier than Earth, but
not so heavy considering their
size
Densities 600 – 1600 kg/m3,
compared with Earth's 5700
kg/m3
Mostly made of gas/liquids?
The Birth of Giants
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In outer solar system, cooler
Less evaporative stripping of
volatile gasses
If sufficiently massive cores
form, can keep even volatile
gasses
These gasses will be
representative of the very
early solar system
The Birth of Giants
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Since early solar system is
largely composed of
Hydrogen, so will gas giants
Rocky or Icy or Slushy core
High-hydrogen atmosphere
has some similarities to
atmosphere in Miller-Urey
experiment
Can form lots of organics
The Birth of Giants
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Large rotating liquid metal
region means large magnetic
field
Jupiter: Significant field
extends out size of the Sun!
Can seriously effect nearby
objects.
The Birth of Giants
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Jupiter in Infrared
Large mass -> high pressure,
temperature at center
Temperature at center of
Jupiter ~ 4 times surface of
Sun!
Collapse from origin of planet
still slowly continuing
Releases heat energy
These planets have a source of
heat
The Birth of Giants
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Jupiter in Infrared
Gas giants emit more heat
than they absorb from Sun
At earlier times, would have
been much hotter
Moons, which are nearby,
heated by their nearby planet
Many of these moons are
large (planet-sized)
Moons might be interesting
for life?
The Composition of Giants
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Structure of gas giant
atmospheres depends on mass
of planet
Lower planet mass -> lower
interior pressure -> may not
be high-pressure enough to
make hydrogen into a liquid
metal.
Rock/Ice cores surrounded by
Hydrogen/Helium gas
The Moons of Giants
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Planets large enough that many
moons were also formed
Many of them planet sized in their
own right
Get heat from planet
Some (Io/Jupiter) effected by planets
magnetic field
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Atmosphere? (Titan, Saturn)
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Water? (Europa, Jupiter)
The Moons of Giants
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Formation: like planets around sun
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Rotating body, disk forms
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Moons generally along plane of
rotation of planet
Tidal Forces
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Tidal forces familiar from Earth
Not due simply to gravitational
attraction (that would just move
the whole body) but the
difference in gravitational force
across the body
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Gravity: inverse square
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Tidal forces: inverse cube
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REALLY matters how close the
object is
Rings
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Most of the gas giants have
rings
Jupiters are very small,
probably transient, and made
largely of dust
Too close to planet, tidal forces
are strong enough to disrupt
moons or prevent them from
forming
Result is material scattered in
orbit around planet
Visiting the outer Solar System
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Pioneer
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Voyager I/II
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Galileo
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Ulysses
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Cassini-Huygens
Pioneer 10,11
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Launched in 1972
Camera, equipment for
measuring gas/magnetic fields
in the solar system, radiation
Now ghost ships
Carry plaque in case ever
discovered
Plaque designed by Carl Sagan
Voyager I/II
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Launched in 1977
Carry cameras, equipment for
measuring gas/magnetic fields
in the solar system
Now at 90 AU (8.4 billion
miles)
Still send trickle of data
Will continue transmitting until
~2020 (not enough sunlight to
power equipment)
Voyager I/II
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Carries a golden record
Has needle, instructions on how
to play it on cover
Contents assembled by Carl
Sagan
Contains music, greetings in 55
langaguges,
natural/atmospheric sounds,
written greetings
http://www.jpl.nasa.gov/flash/voyager_record/index.htm
Voyager I/II
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Travelled past Jupiter, Saturn
Voyager II then flew by Uranus
and Neptune; Voyager I stopped
by Titan (largest moon of Saturn),
trajectory then sent it out of plane
of galaxy
Ulysses
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Sent to examine magnetic field,
radiation from Sun, esp. poles
Sent to Jupiter for slingshot out of
plane of ecliptic
Also obtained magnetic field data
from Jupiter
Galileo
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Launched 1993
Study Jupiter's atmosphere,
satellites, magnetosphere for 2
years.
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Made encounters with asteroids
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Arrived at Jupiter, Dec 1995
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Significantly advanced our
knowledge of the Galilean moons
At end of mission was burned up
in Jupiter's atmosphere to avoid
contaminating moons
http://www.jpl.nasa.gov/videos/quicktime/galileo.qtl
Galileo
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Took pictures of direct impact of
comet into Jupiter in 1994
Cassini-Huygens
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Will arrive at Saturn later this
year (July)
Already taking pictures
Will send a probe (Huygens) to
Titan
Planets of Interest
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Where might life be?
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Gas Giants?
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Moons?
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Europa
Titan
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Iapetus
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Gas Giants
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Convection is a fundamental
process
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Happens everywhere
Fluid heated at bottom rises,
cools, falls back down
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Gas giants have hot centers
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Large-scale motions
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Mix material
Gas Giants
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Makes it difficult to imagine
life forming
No real surface to live on
Chemicals constantly being
mixed around
No originally contained
environment (`protocell')
Moons
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Gas giants have planet-sized
moons
At least one (Titan) has a
significant atmosphere
Another (Europa) very likely
has liquid salty water under a
layer of ice
Europa
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Very suggestive it has a liquid
underneath
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No cratering
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Many fractures, ridges on
surface
What would this mean for life?
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If some source of energy
on inside (geothermal,
chemical), very real
possibility of some sort of
life
Titan
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Very Cold
Massive, Cold enough to have
an atmosphere (1.5 x as dense
as ours!)
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No oxygen
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No liquid water
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Hydrogen rich
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Interesting organic chemistry
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Lakes of hydrocarbons?
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Huygen probe 2005
Iapetus
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Moon of mystery
Side facing away from Saturn is
very, very dark
Much less light reflected than
bright side
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How did this happen?
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What is the dark material?
How Unique is Earth?
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What is special about Earth?
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How important/rare are those things?
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How many such planets are there likely
to be?
Earth
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Atmosphere
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Large surface gravity
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Reasonable temperature
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Rocky srface
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Large moon
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Lots of heavy elements
How Important/Rare are these?
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Heavy elements;
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Likely ubiquitous in
planets around Pop I stars
How Important/Rare are these?
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Rocky Surface
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Can happen if there is
heavy elements (see
above)
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Probably true of all
planets close enough to
have liquid water
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(But planet migration)
How Important/Rare are these?
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Atmosphere
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Requires not too close to
sun
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Requires massive enough
planet
How Important/Rare are these?
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Reasonable Temperature
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`Goldilocks zone’
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Needs to be right distance
to star
How Important/Rare are these?
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So we require
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Rocky Planet
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Of the right mass
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At the right distance from
the star
Habitable Zone
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Corresponds to further than
Venus to about Mars distance
for our Sun
Using inverse-square law, could
calculate for other stars
Main requirement: liquid water
in the presence of an
atmosphere.
Habitable Zone: Binary Stars
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About half of all stars are in
binary systems
Stars orbit a common center of
mass (more on that next week)
Can planets have reasonable
orbits in such systems?
Yes, but must orbit one star or
be far away from both;
`Figure 8’ orbits aren’t stable
Reading for Next Class (Apr 23)
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Chapter 17: The Discovery of Extra-Solar
Planets
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Techniques for finding planets
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Results
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Looking closer
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Atmospheres?
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PlanetQuest