MARS
Printable
version
March
30, 2000
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Mars
Preview
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Mars
overview
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Observing
Mars from Earth
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Mars
surface
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Mars
atmosphere
Mars
Overview
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Mars rotation, tilt of axis
very similar to Earth's
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Diameter 1/2 of Earth's
Observing
Mars from Earth
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Mars is a superior planet
(further from the Sun)
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Best time to observe is at
opposition
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Mars orbit is more elliptical
than Earth's
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some oppositions are more
favorable than others
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opposition distance varies
from 0.37 to 0.68 AU
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Surface features on Mars
allow measurement of rotation
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Huygens observed in 1659
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Cassini in 1666
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Cassini observed polar ice
caps on Mars
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William Herschel, late 1700s
measured tilt of Mars' rotation axis
Amateur telescope view
of Mars
Mars
has NO CANALS
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A tale of miscommunication
and influence
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Martian day similar to Earth
day
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Seasonal variation on Mars
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what causes seasons?
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polar caps shrink in Martian
summer
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dark markings stand out more,
look greenish
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People wondered if Mars had
life like Earth
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Early telescopic views of
Mars were fuzzy
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Observations made by eye,
recorded with hand drawing
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Eye plays tricks
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Hand drawings are schematic
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However, rotation, period,
axis could be measured repeatably
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Giovanni Schiaparelli in
1877 "discovered" canals
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saw 40 straight line features
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called them "canali" which
is Italian for "channels"
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Millionaire Percival Lowell
built observatory to study canals
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saw 160 canals
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Lowell observatory still
prestigious today
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H.G. Wells War of the
Worlds published in 1898
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Edward Barnard, 1894 "to
save my soul, I can't believe in the canals as Schiaparelli draws them."
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hushed up observations of
craters
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craters would suggest dead,
moon-like surface
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Eugene Antoniadi ~1920 debunked
canal myth
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showed "canals" are unconnected
dark spots
The
Real Surface of Mars
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Observed close up starting
in 1960s with Mariner 4,6,7
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Craters rediscovered
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Lots of craters
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Mars surface must be old
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more like the moon than the
Earth
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craters flat at the bottom
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Clouds on Mars (visible from
Earth)
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Dust storms probably fill
craters
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very fine dust
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3 billion years of dust storms
haven't completely filled them up
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More craters in the southern
hemisphere
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evidently more geologic activity
in northern hemisphere
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Guessing based on the moon,
Mercury, Venus, what geologic activity happened on Mars?
Viking image of dust
storm
Volcanos
on Mars
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Evidently some parts of Mars's
crust are weaker than other parts, or mantle pushes harder in some places
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Crust is pushed up in these
places
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Tharsis Rise
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Elysium Rise
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Volcanos happen in/near Tharsis
Rise
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Hot
spot volcanism
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Also in the state of Hawaii
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Olympus Mons 3 times taller
than Everest!
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Martian volcanos extinct
now
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being smaller than Earth
Mars cooled off faster
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Valles Marineris likely formed
at same time as Tharsis Rise
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stretch mark
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technically: rift valley
Mons left to right: Olympus,
Arsia, Pavonis, Ascraeus
Olympus Mons
Evidence
for Water on Mars
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Canyons (not to be confused
with canals, which don't exist)
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Flood plains
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Polar ice caps
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Top layer of ice cap is probably
frozen CO2 (dry ice)
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Where is the water now?
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locked into ice at poles
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locked into ice in the soil
(permafrost)
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meteor impacts can melt permafrost
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Liquid water cannot exist
on Mars now
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atmospheric pressure too
low
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liquid water would boil away
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Mars probably had a thicker
atmosphere and was warmer at one time
Mars
Atmosphere
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Very
thin (0.007 pressure of Earth's atmosphere)
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95%
CO2
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3%
Nitrogen
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Trace
argon, oxygen, CO, water vapor
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Evidence
of liquid water suggests was thicker at one time
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Had
greenhouse effect?
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Why
doesn't Mars have a greenhouse effect now?
Mars
atmosphere history
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Venus,
Earth, Mars probably started out about the same
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First
no atmosphere, then volcanos spew out gas
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Lots
of H2O, CO2, N2 in atmosphere
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Greenhouse
effect from H2O, CO2
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Water
clouds, rain, oceans
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Venus
too hot kept water vapor in atmosphere
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runaway
greenhouse effect
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Mars
too cold, water rained down
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CO2
dissolves in liquid water
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H2O
+ CO2 + rock = carbonate rocks (limestone)
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Martian
CO2 and water vapor depleted
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Greenhouse
effect becomes less efficient (smaller blanket)
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Gets
colder, less water evaporates...
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reverse
runaway Greenhouse effect
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Earth
just right: has mild Greenhouse effect
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moderated
by O/CO2 balance
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without
greenhouse effect, Earth would be 35o C cooler (frozen)
Mars
Review
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Mars
overview
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Observing
Mars from Earth
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Mars
surface
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Mars
atmosphere