Chapter 12: History of Mars

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Chapter 12 History of Mars

Rovers view of Mars
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Why Mars is prime target for search for life

• 1. Direct evidence that Mars had liquid water in
  past and possibility of subsurface water now.
• 2. Has an atmosphere of CO2 and N2
• 3. Planet is cold and dry good for preserving
  organic remains of life.
• (see C. Mckays article in our book)

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Mars Rover Mission Objectives

• Search for and characterize a variety of rocks
  and soils that hold clues to past water activity.
  Samples will include those that have minerals
  deposited by water-related processes such as
  precipitation, evaporation, sedimentary
  cementation, or hydrothermal activity.
• Determine the distribution and composition of
  minerals, rocks, and soils surrounding the
  landing sites.
• Determine what geologic processes have shaped the
  local terrain and influenced the chemistry. Such
  processes could include water or wind erosion,
  sedimentation, hydrothermal mechanisms,
  volcanism, and cratering.
• Perform "ground truth" -- calibration and
  validation -- of surface observations made by
  Mars orbiter instruments. This will help
  determine the accuracy and effectiveness of
  various instruments that survey Martian geology
  from orbit.

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• Search for iron-containing minerals, identify and
  quantify relative amounts of specific mineral
  types that contain water or were formed in water,
  such as iron-bearing carbonates.
• Characterize the mineralogy and textures of rocks
  and soils and determine the processes that
  created them.
• Search for geological clues to the environmental
  conditions that existed when liquid water was
  present. Assess whether those environments were
  conducive to life.

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Orbit of Mars and several recent oppositions
(25 angular size at best
e 0.093, a1.52 AU, aphelion 1.67 AU,
perihelion 1.38 AU, -gt variation in light
during Martian year of 45
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• Mars/Earth Comparison
• Mean Distance from Sun 1.52 AU
  
  
• 
  1 AU
• Average Surface Pressure 0.5 1kPa
• 
  101.3 kPa
• Diameter 4,220 miles
• 7,926
  miles
• Tilt of Axis 25 degrees
• 23.5 degrees
• Length of Year 687 Earth Days
• 365.25
  Days
• Length of Day 24 hours 37 minutes
• 23 hours 56
  minutes
• Temperature Average -60 degrees C
• Average 15 degrees
  C
• Incident solar radiation 149 W/sq m.
• 
  344 W/sq m.

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Space craft images of Mars
Polar cap
Hubble Space Telescope Image
Viking (1976)
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Mars in true colour (Viking mission image)
Northern hemisphere rolling volcanic
(lunar-like) plains. Southern hemisphere
heavily cratered highlands 5 km above lowlands in
north. Major feature Tharsis bulge, which is 10
km higher than rest of surface
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Map by Mars Global Surveyor used laser
altimeter
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Hellas Basin lowest region on Mars, 3000 km
across and 6km below average level of Martian
surface impact crater?
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Surface of Mars Northern hemisphere sourthern
highlands

• Northern hemisphere rolling volcanic plains
  (like lunar maria) much larger lava plains than
  on Earth or Moon less cratered than southern
  highlands therefore younger
• b) Southern highlands cratered and 5 km above
  northern hemisphere original Martian crust

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Tharsis - the only continent on surface of Mars
Tharsis bulge major geological feature of Mars
- less cratered than northern plains so is
relatively young 2-3 billion years old -
depressions hundreds of km wide, up to 7 km deep
- Vallis Marineris crustal forces push out
Tharsis region, and this valley is where crust
cracked feature is 4000km long (Grand Canyon
fits into small crack in this structure)
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Comparison, to scale, with the Grand Canyon which
is 20km wide and 2 km deep. Cracks in Valles
Marineris at least 2 billion yrs old.
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Olympus Mons largest volcano known in the solar
system 700 km base and 25 km in height!
Compare Mauna Kea base 120 km, height 9 km from
ocean bottom
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Volcanism on Mars

• Volcanoes on Mars sit on top of hot spots in the
  underlying Martian mantle (like shield
  volcanoes Hawaiin islands)
• No indication of continental drift on Mars no
  volcanic activity of this kind
• Height of volcano lower surface gravity of
  planet (40 of Earth) -gt volcano can be built up
  2.5 times higher than on Earth (assuming similar
  strength of crusts)
• Tharsis active 100 million yrs ago (based on
  cratering record)

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Martian Atmosphere

• Pressure is 1/150th of Earths atmosphere
• Composition (by volume)
• 95.3 CO2
• 2.7 N
• 1.6 Argon
• 0.13 Oxygen
• 0.03 water vapor
• (Earth 21 O 78 N)
• Noon summertime
• T300K
• Night little heat retention T drops by 100 K
• Storms begin in southern hemisphere, carrying
  dust into stratosphere covering the planet

On average, temperatures on Mars are 50 K cooler
than Earth
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Polar caps frozen Carbon Monoxide and Water Ice
Freezing point of CO2 150 K CO evaporates
during Martian summer leaving small cap of water
ice CO2 refreezes during Martian winter
producing a larger cap. Addition and subtraction
of CO2 from atmosphere mcauses large pressure
fluctuations over a season (30). Southern
(left,) and northern caps (right mostly water)
in summer 350 and 1000 km diam.
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Water on Mars Impact cratering,
and runoff channels
a) Large lunar crater (Copernicus) - powdery
ejecta b) Mars crater Yuty (18 km diam)
fluid-like ejecta permafrost melted during the
impact
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Runoff channel on Mars 400 km long, 5 km
wide
Compare Mars channel, with Red River running to
Mississippi
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Flow around obstacles (craters)

• The flow rates around these obstacles were about
  100 times larger than the flow rate of water
  through the Amazon river. Islands in this
  image are 40 km long.
• (Flow through Amazon is 100,000 tons per second
  largest river system on Earth).
• Flooding shaped these channels 3 billion yrs
  ago.

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Where did all the water go?

• Mars had rivers, lakes, and possibly oceans .
• 4 billion years ago, climatic change leads to
  freezing of rivers, water forming permafrost
  (like Canadian tundra)
• Giant flash floods occur 3 billion years ago in
  wake of volcanic activity that melts the
  permafrost.
• Once volcanic activity ceased, water froze into
  permafrost.

Site of ancient ocean on Mars?
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How much water was/is there?

• To explain existing erosional features need
  0.001 0.01 Earth oceans worth
• Evidence for more water earlier high levels of
  deuterium in Mars atmosphere -gt most of
  hydrosphere lost to space
• -gt more than 0.1
  Earth oceans
• Shorelines of northern basin measured by Mars
  Global Surveyors (MGS) laser altimeter
• -gt could hold .01
  Earth oceans
• within basin.
  
• Minerals From MGS infrared spectrometer
  measure infrared spectra to find an iron oxide
  (grey hematite), which may be related to
  formation in presence of water.
• -gt strategy for surface rovers.

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• Properties of water on Mars
• - Triple point of water is 0.61 kPa
  water does not exist at liquid at lower pressures
• -gt low present pressure on Mars means
  water is absent in liquid form.
• - at surface pressure of 1kPa, water boils
  at 7C. Even at 0C, water close to boiling and
  this carries away a lot of heat.
• Relevance to Mars
• - low elevation of northern plains -gt
  pressure is higher and above the triple point of
  water (0.7 kPa) so liquid water could be
  present
• - high elevation of southern polar
  regions has too low a pressure -gt liquid water
  unstable

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Roving Mars for water, and life .
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Opportunity at Victoria crater
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Design of Viking experiments

• Prolytic release exp (PR)
• - detect microbes in soil, consuming CO2 and
  using light
• Gas exchange exp (GEx)
• - detect gas release by microbes when
  organics added to soil
• Result rapid O2 release when soil exposed
  to just water vapour response persists even
  after soil sterilization. ( not biological)
• Labelled release exp (LR)
• - detect release of CO2 from microbes when
  radioactively tagged organic nutrients added
• Result release of CO2 eliminated on
  sterlization (biological?)

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• Gas Chromatograph Mass Spectrometer (GCMS)
• - no detection of organics in soil to
  one part per billion.
• - major reason why results of exps
  interpreted as due to reactivity of martion soil.
  
• Why? In Atacama desert (driest place on
  Earth), even soil without detectable microbes
  have detectable organics
• Caveats Exps based on trying to culture
  microbes this is now kown that culture exps on
  Earth fail 90 of the time.
• - develop culture free methods for future
  exps.

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Is there life on Mars?
Viking lander results

• Soil samples taken by Viking lander looked for
  gas release due to metabolic activity no
  evidence for metabolism
• Martian meteorite contains PAHs and perhaps
  long, rod-like bacteria (0.5 microns long)?
• No concrete evidence yet for life however
  presence of water beneath surface very important.

ALH84001
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RoversPhysical evidence for water spherules
seen in Eagle Crater rock outcrop site.
Not volcanic but gypsum (most common sulfate
mineral) crystals. Fell out of sedimentary rock
perhaps due to wind erosion.
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Rover results Opportunity in Eagle crater

• Rock outcrops in crater hold evidence that liquid
  water was stable and present on Mars
• Mossbauer spectrometer results (gamma ray
  spectroscopy) iron-rich sulfate (hydrated
  minerals) called jarosite, requiring presence
  of water to form.
• Evaporation sequence of minerals variation in
  concentrations of elements going down through
  rock, progressively deposited as water evaporated
• Spheruleseroded out of rock
• Layering of rock, angled, cross bedded
  sedimentary rock laid down in flowing water.

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History of water on Mars

• Origin of water Earth water acquired from late
  impacts of large Mars sized planetesimals?
• - for Mars, such collisions would be
  destructive must have accreted from many
  smaller impacts
• - implies Mars gets water from
  asteroids and comets, delivering total of 1/20
  ¼ Earth oceans worth with D/H 2 times Earth
  ocean.
• - 2nd possibility local origin, Mars
  formed in a cooler, wetter part of nebula water
  ice added directly during its formation locally?

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• Warm climate on early Mars?
• - Heating by green house requires much
  more CO2 than on Earth because
• i) solar luminosity lower at earlier
  times by 70
• ii) Mars is more distant than Earth, so
  black body T is lower to begin with,
• -gt needed atmosphere with several times
  pressure of Earths and 10,000 times pressure of
  CO2 than Earth!
• - greenhouse gas eventually lost to space
• - test idea using N(15)/N(14) isotopic
  ratios

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• Drying and freezing of Mars
• - High erosion rates on early Mars due
  to
• warm and wet surface conditions - eg. heavy
  erosion of large impact craters in older southern
  hemisphere material
• - on younger terrains, much less
  erosion (possibly by several thousand times)
• -gt early and quick end to wet era.
• - water loss tested by D/H measurements
• i) 5 times Earth ocean
• ii) 3 times ancient Mars meteorites
  
• iii) much less than loss on Venus
  -gt water stored by trapping in crust?