Transcript Lecture (Powerpoint)

Announcements
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Passing out marks-so-far today with assignments
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½ of available marks now given out
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Can always do `bonus assignments' (worth 2 credits)
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Find current news article relevent to the
course (1 credit)
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Briefly describe it and its relevence to the
course (1 credit)
The Search: Mars
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A Short Biography of Mars
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The Planet and its History
The History of Mars Exploration
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Past
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Current
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Future?
The Search for (past) Life on Mars
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Viking Experiments
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Microbial Fossils
A Portrait of Mars as a Small Planet
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Mars
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The atmosphere of Mars
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How it came to be that way
Mars
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Red planet between Earth and
Asteroid Belt
Half again as far away from Sun
as the Earth is
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Expect it to be ~100o F
colder than Earth on average
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Average too cool for water
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Peak temps ~ 70o F (but -130
at night!)
Mars
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Near asteroid belt
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Large impacts can blow off
significant rocky material
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Likely more collisions than
Earth
Meteorites
As well as gases (atmosphere)
Mars
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~1/2 radius of Earth
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~1/10 mass
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~40% surface gravity
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Force of a 1 lb weight less
than ½ lb on Mars
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Less gravity holding the
atmosphere in place
Mars
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Too little gravity to be able to hold
onto a significant atmosphere
Atmospheric pressure less than
1% of Earth's
Evaporation
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What causes evaporation of liquid,
and what prevents it?
Evaporation
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What causes evaporation of liquid,
and what prevents it?
Fastest moving water (say)
molecules can escape into
atmosphere
Water molecules in atmosphere
can collide into water and become
part of the liquid
Balance is reached when
evaporating water = condensing
water
Evaporation
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Can change balance:
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Little water in atmosphere,
evaporation happens faster
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(Why feel so sticky on a
humid day)
If air pressure is very low,
evaporated water molecules
can move very far away
from pool of water
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Fewer around to condense
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Faster evaporation
Evaporation
Boiling Point at Alt it ude
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220
Boiling Pt of Wat er (F)
210
200
190
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180
170
160
150
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140
130
120
110
100
0
2000
5000
Alt it ude (ft )
7500
10000
Effect of atmospheric pressure
happens on our own planet
Reason for `high-altitude cooking
instructions' on some boxes
Higher altitude -> lower air
pressure -> evaporation is easier > lower boiling point
Evaporation
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Martian atmospheric pressure <
1% of Earth's
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(Earth's atmosphere at 15
miles / 80,000 ft)
Water boiling point is so low that
any liquid water evaporates
immediately
No free water possible on surface
Evaporation
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But water ice DOES exist on
Mars:
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Polar ice caps
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Mostly (on top) dry ice
(frozen CO2)
Underneath, visible when
CO2 has sublimated, water ice
Quite likely some trapped
under surface: `permafrost'
Atmospheric Pressure
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Atmospheric pressure is
seasonal
Dry ice caps melt
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Increase CO2 in
atmosphere
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Increase atmosphere
pressure
Dry ice caps re-freeze
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Pressure decreases
The Reasons for the Seasons
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Earth's (and Mars') axis is
tilted
Earth: 23.5o (Mars: 25.9o)
Tilt stays in same direction
as planet orbits Sun
The Reasons for the Seasons
Summer
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Winter
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Sun comes in at different
angle when planet is at
different positions
Summer:
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Light most direct
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Sun closest to being
overhead
Winter
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Comes in at angle:
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Same amount of light
covers larger area
Increased reflection
The Reasons for the Seasons
Winter: Bears Lose
Fall: Cubs win
(effective 2003)
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Spring: Bulls Lose
Orientation changes over
course of year
Another effect: Earth is
slightly further from Sun in
(Northern Hemisphere)
Winter than in Summer
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Only ~1% effect (5oF)
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Effect of orientation
~16% effect (90oF)
Ecliptic
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Because of Earth's tilt, equator
(and rotation) do not line up with
plane of the solar system
Solar system objects (Sun, Moon,
planets) apear to lie along an arc –
ecliptic
Ecliptic
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Starmap for tonight, 9pm
Planets are along plane of solar
system
Appear on Earth to along an arc
Mars visible these days early at
night towards the East, even from
Chicago
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Bright reddish `star'
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Near a bright greenishyellow `star' (Venus)
How Mars Came to Be This Way
Large Enough for Atmosphere
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Distance from Sun makes global
liquid water difficult but not
impossible
NO ATMOSPHERE
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Liquid water quickly
evaporates
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No greenhouse effect to warm
planet, regulate temp.
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No ozone to protect from UV
Not Large Enough for Atmosphere
The History of Martian Exploration
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Past explorations
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Current Rover Missions
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Future Plans
Exploration of Mars Today
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So many recent missions to
Mars that it's becoming
almost anticlimatic
News filled with discoveries
from current rovers
Still very difficult:
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Success rate low!
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Scientists can't go there
at whim yet
Observations of Mars from Earth
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Early telescope observations:
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`observations' of canals
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Improved telescopes
showed this not to be the
case
Later, radio observations
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Surface temperature
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Crude radar maps of
surface
1960-2: Korabl (`Marsnik')
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Attempted Russian Probes
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4 attempted flybys, 1 attempted landing
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Most barely made it past Earth orbit,
one was lost between Earth and Mars
1964: Mariner, Zond
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Mariner 3, 4 (USA): attempted flyby
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Mariner 3: Couldn't make it to
Mars
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Mariner 4: First flyby, close up
pictures
Zond 2 (USSR): Russian flyby, descent
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Lost on its way to Mars
1969: Mariner, Mars 1969
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Mariner 6,7: Identical flyby craft
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Mariner 4: First flyby, close up
pictures
Mars 1969A/B: Russian flyby, descent
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Didn't survive takeoff
1971: Mariner, Mars 2/3: Orbiters
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Mars 2/3 (USSR): First orbiter of
another world
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Measured temps, magnetic fields
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Sent probe, 1 crashed too fast,
other survived 20 hours Mariner
8 didn't make it
Mariner 9: Orbited, obscured by storms
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First close-up views of moons of
Mars
1973: Mars 4/5/6/7 (USSR)
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Mars 4: Brakes didn't work; flew by
instead of orbited
Mars 5: Successful Orbit, pictures
Mars 6: Descent, sent data from
atmosphere before shutting down, but
data garbled
Mars 7: Missed Mars entirely
1975: Viking 1,2 (USA)
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Identical Orbiter + lander
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Orbiters searched for safe
landing places
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Extensive weather
measurements, chemistry/biology
experiments
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Sent several thousand images,
data
1988: Phobos 1,2 (USSR)
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Lost due to human error (Phobos 1),
computer malfunction (Phobos 2)
1988-1992
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1988: Phobos 1, 2 (USSR)
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Lost due to human error (Phobos
1), computer malfunction
(Phobos 2)
1992: Mars Observer (USA)
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All contact lost 3 days from Mars
Very Recent Mars Missions
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1996:
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Mars 96 (USSR): Didn't
successfully leave Earth
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Mars Global Surveyor (USA)
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Looking for places to send
Pathfinder
Still sending back data
Mars Pathfinder
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Probe with some sensors
Test of new technologies,
techniques
1998: Less Successful
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Nozomi (Japan)
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Navigation problems
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Could not reach Mars at expected time
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Unable to orbit Mars
Mars Climate Orbiter (USA)
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Crashed into Mars after mistake in
converting units in probe computer
programming
1998-9: Less Successful
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Nozomi (Japan)
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Navigation problems
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Could not reach Mars at expected time
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Unable to orbit Mars
Mars Climate Orbiter (USA)
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Crashed into Mars after mistake in
converting units in probe computer
programming
Mars Polar Lander (USA)
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Signal lost near Mars: Navigation errors?
2001: Mars Odyssey
(NASA)
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Orbiter
Build global map of telements, minerals on the
Mars surface
Determine the abundance of hydrogen in
subsurface. -> hidden deposits of water ice?
Structure of the Martian surface.
Radiation environment between the Earth and
Mars and in low Mars orbit (radiation-related risk
to human exploration)
Communication relay Spirit/Opportunity/Beagle
2001: Mars Express
(Europe)
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Orbiter + Lander/Rover (Beagle)
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Beagle lost
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Image globe in 3D
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Build accurate picture of meteorology/climage
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Communications Relay
2003: Spirit, Opportunity
(USA)
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Search for/study many types of rocks
and soils that might hold clues to past
water activity.
Maps showing the locations of
different kinds of rocks and soils
around the landing sites.
What forces have shaped the
landscape
Search for minerals that contain
water/formed in water.
Identify minerals, how made
Clues to what environment was like in
past
The Search for Life on Mars
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Pictures of surface
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Viking biology experiments
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Meteoritic `fossils'
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Future?
Venus
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Closest to Earth
¾ as far away from Sun as
Earth is
Very similar to Earth's size,
density
Covered by thick, opaque
clouds
Reading for Next Class (Apr 16)
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Chapter 15: The Outer Solar Systen
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History of Outer Solar System Exploration
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The Nature of Gas Giants
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Atmosphere
Chemistry
The Moons of Jupiter, Saturn, Uranus,
Neptune
Chapter 16: How Unique is Earth?
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Necessary Resources
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On Having a Large Moon
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Staying alive by accident