Introduction to Mars

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Introduction to Mars Part Two
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Top Ten Questions about Mars
  1. Was Mars ever a habitable planet? Did it
sustain life? Was the early Archean on Earth much
different from early Mars? 2. Did Mars possess
abundant surface water in its early history? Did
seas or lakes of water exist? How much water is
now in the Martian interior?  3. What is the
nature of weathering on the Martian surface? 4.
What has been the composition and evolutionary
history of the Martian atmosphere? Did early
Mars possess a much larger or smaller
atmosphere? 5. What has been the volcanic history
of Mars over time? What different types of
volcanic rocks exist near the surface? What are
the ages of the major volcanoes? Have there been
catastrophic volcanic episodes? Did early Mars
have a magma ocean? 6. Did Mars ever have plate
tectonics? What is the nature of crustal
recycling? How much ancient, primary crust has
survived? Where would we look?  
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Top Ten Questions about Mars (cont.)
7. What has been the cratering rate on Mars over
time and how can this be used to age date surface
units? 8. What are the absolute radiometric ages
of different rocks and provinces near the Martian
surface? What has been the nature and history of
internal Martian differentiation and of magma
source regions? 9. What is the overall chemical
composition of Mars and how does it compare to
other planetary bodies in the solar system? What
is the nature of the Martian core and mantle?
What is the mineralogy of the Martian interior?
10. What are the geophysical properties (heat
flow, seismic activity, etc.) of the Martian
interior and what do they reveal about the
internal structure of Mars?
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Mars Big Science Goals

• How does the composition of Mars differ from the
  Earth's and how have the two planets evolved
  differently?
• How does the composition and state of the
  interior of Mars differ from the Earth's?
• Is Mars still geologically active?
• What resources are available at the surface for
  our future use?
• Was there an early dense atmosphere on Mars?
• Did Mars once have oceans?
• What changes in climate has Mars experienced over
  its geologic history and what caused those
  changes?
• How stable is the climate of Mars today?
• Did chemical evolution take place on Mars
  leading to the formation of prebiotic organic
  molecules?
• Did chemical evolution lead to the formation of
  replicating molecules, i.e. life?
• If life once arose, is it to be found anywhere on
  Mars today?

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Open Issues

• Why are the northern and southern hemispheres of
  Mars so different?
• Why are the northern and southern polar caps
  different?
• Is there still active volcanism on Mars?
• What exactly caused the erosion patterns that
  look so much like stream beds on Earth?
• How much subterranean water is there?
• Mars remains at the top of the list of possible
  life-bearing planets. The Viking probes found
  little evidence of life on Mars. But they sampled
  only two isolated locations. Is there life
  elsewhere or was there life at some time in the
  past on Mars? The recent meteoritic evidence
  needs to be confirmed. Ultimately, a sample
  return mission will be necessary.
• The future of Mars exploration seems bright, but
  limited to modest missions. Several robotic
  missions are planned by NASA and others for this
  decade. A human expedition is at least 20 years
  away.

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Mars Exploration Rovers
Mars Phoenix
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Spirit Landing Ellipse
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Gusev Crater
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Gusev Crater
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True-color Pancam mosaic images (Figure 2e is
approximate color rendering because some filters
are missing) of basaltic rocks in Gusev Crater.
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Olivine Basalts at Gusev
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Gusev Olivine-rich Basalts
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Trace Elements in Gusev Basalts
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Mars Surface Composition Measured from Orbit
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No Martian Meteorite Compositions Seen From Orbit
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Olivine Detection from Orbit
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Mars Global Surveyor Thermal Emission
Spectrometry
Gusev
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Meridiani Planum
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Opportunity at Meridiani Planum
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Possible Mineralogies for Merdiani Sediments
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Jarosite
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Jarosite formation in Earth ore deposits
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Thermodynamic Stability of Jarosite
Oxidizing and Acidic
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Standing Body of Water Left Its Mark in Mars Rocks
This magnified view from Opportunity of a portion
of a martian rock called "Upper Dells" shows fine
layers (laminae) that are truncated, discordant
and at angles to each other. Interpretive black
lines trace cross-lamination that indicates the
sediments that formed the rock were laid down in
flowing water. The interpretive blue lines point
to boundaries between possible sets of
cross-laminae
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Blueberries at Opportunity site are rich in
mineral hematite (Fe2O3). Aqueous origin?
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Meridiani Planum
The emerging picture is of a salt-laden, often
corroded planet that had standing water early in
its history. Volcanic emanations made that water
acidic enough to leach salt from the rock and lay
it down in thick beds, and water beneath the
surface seems to have altered rock as well.
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False color Pancam image of the upper portion of
the stratigraphic section at Karatepe West,
showing rover wheel tracks and seven of the
eleven RAT holes made during the descent. Image
acquired on Sol 173 using Pancam's 753 nm, 535
nm, and 432 nm filters, L2, L5, and L7.
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Approximate true color Pancam panorama of eolian
ripples on the Meridiani plains. Image acquired
on Sols 456 to 464 part of the Rub Al Khali
panorama acquired from Purgatory Ripple
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Why are Martian Meteorites different from surface
samples?
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Bounce rock RATted by Opportunity is a match for
Martian meteorite
Bounce
Martian meteorite
Data from alpha particle x-ray spectrometer
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Looking for Earth Analogs
Navajo Sandstone, Utah, Earth
Blueberries, Meridiani Planum, Mars
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Utah
Mars
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No location on Earth closely resembles Meridiani
Planum, but many sites share aspects with it.
Chemical analogs include the acid mine drainage
of Rio Tinto in Spain, where microbial activity
exists in a mineral assemblage resembling that of
Meridiani Planum. Does martian geochemistry
resemble a global acid mine pollution site of
ochre and sulfate mineralization? Another new
Mars model is based on the hypersaline Permian
Basin in North America. In that classic salt
sea, repetitive cycles of evaporation and
flooding produced a layered, salty rock sequence
(panels J to O). One can speculate that the
Permian Basins biogenesis, salt-trapping, and
slow release of hydrocarbons may also serve as an
analog for methane-involving processes on Mars.
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Alternative View
Volcanic surge deposit (Maar)?
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Endurance Crater, Meridiani Planum, Mars
Kilbourne Hole, NM, USA, Earth
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Meteorites on Mars
Iron Meteorite at Meridiani
Mesosiderite? at Meridiani
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Mars Volcanism
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Montes (mountains)
Ascraeus Mons
Pavonis Mons
Arsia Mons
The montes or large shields are likely basaltic
(like the volcanos in Hawaii and Iceland), very
large (Olympus Mons is the largest mountain
feature known anywhere in the solar system), and
have very gentle slopes of six degrees or less.
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Olympus Mons and Tharsis superimposed on Western
US
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Location and names of major volcanoes and plains
on Mars. Solid black patches represent major
volcanic edifices.
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Elysium Planitia is the second largest volcanic
region on Mars. It is located on a broad dome
that is 1,700 by 2,400 kilometers (1,060 by 1,490
miles) in size.
Elysium Mons is the largest volcano in this
region. It has base dimensions of 420 by 500 by
700 kilometers (260 by 310 by 435 miles) and
rises 13 kilometers (8 miles) above the
surrounding plains.
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Did Mars Have Early Plate Tectonics?
 Like Mercury and the Moon, Mars appears to lack
active plate tectonics at present there is no
evidence of recent horizontal motion of the
surface such as the folded mountains so common on
Earth. With no lateral plate motion, hot-spots
under the crust stay in a fixed position relative
to the surface. This, along with the lower
surface gravity, may account for the Tharsis
bulge and its enormous volcanoes. There is no
evidence of current volcanic activity, however.
But there is new evidence from Mars Global
Surveyor that Mars may have had plate tectonic
activity in its early history.
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Comparison of global magnetic fields on Earth
Mars
Purucker,2000
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These images are an artist's concept of the
process that may have generated magnetic stripes
in the crust of ancient Mars. In the left image,
the blue arrows and compass needle indicate the
direction of the magnetic field. The
yellow-orange shape represents a pool of molten
rock (magma) upwelling beneath the Martian crust.
The red and blue bands are magnetized crust on
either side of a spreading center, or rift. The
bands of magnetized crust apparently formed in
the distant past when Mars had an active dynamo,
or hot core of molten metal that generated a
global magnetic field. Mars was geologically
active, with molten rock rising from below to
cool at the surface and form new crust. As the
new crust cooled and solidified, the magnetic
field that permeated the rock was "frozen" in the
crust. Periodically, conditions in the dynamo
changed and the global magnetic field reversed
direction. This is illustrated in the right
image, with the red arrows and compass needle
indicating a new magnetic field direction.
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The stripes on Mars are not only wider than those
on Earth, but they are also stronger magnetized.
This may mean that the Martian crust could have
been generated at a greater rate, or the magnetic
field of Mars, generated by its core, alternated
less frequently than that of Earth.
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Martian Interior
The interior of Mars is known only by inference
from data about the surface, SNCs, and the bulk
statistics of the planet. The most likely
scenario is a dense core about 1700 km in radius,
a rocky mantle somewhat denser than the Earth's
and a thin crust. Data from Mars Global
Surveyor indicates that Mars' crust is about 80
km thick in the southern hemisphere but only
about 35 km thick in the north. Mars' relatively
low density compared to the other terrestrial
planets indicates that its core probably contains
a relatively large fraction of sulfur in addition
to iron (iron and iron sulfide).
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Bertka Fei, 1997
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Martian Core
If the Martian core is dense (composed of iron),
then the minimum core radius would be about 1300
kilometers. If the core is made out of less-dense
material such as a mixture of sulfur and iron,
the maximum radius would probably be less than
2000 kilometers.
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Liquid Core?
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Light Element Affects Core Size
FIGURE 2.1 Density profiles for a range of model
core compositions (solid lines). For each core
composition, the thickness of the low-density
crust is adjusted to give the correct mean
density and moment of inertia for Mars. Dashed
lines indicate the depth, or pressure, of the
core/mantle boundary for model core compositions.
The crust-mantle-and-core profile shown (heavy
line) assumes a 50-km, 3.0-g/cm3 crust.
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Early Mars Magma Ocean?