Martian Oceans

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Martian Oceans

• Evidence for a Northern Ocean on Mars

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Overview

• Where could the water have come from? (Origin of
  water on Mars)
• Could the Martian climate have been favorable for
  a liquid ocean? (Climate conditions and obliquity
  simulations)
• Is there evidence that an ocean formed? (MOLA and
  MOC images)

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What is the importance of possible oceans on Mars?

• Life on Earth formed in the ocean. If Mars had an
  ocean, this would be the best place to look for
  life on Mars.
• If Mars did have an ocean, then Earth is
  non-unique. It is possible there are other
  planets in the universe may have them as well
  which means extra-terrestrial life in the
  universe is possible.

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Origin of Water on Mars

• Lunine et al. 1 discuss
• It was too hot for water to form at distances of
  1 AU.
• The water must have been acquired from material
  that formed at larger distances from the sun.
• Earth was formed (and acquired its water) from
  planetary embryos which grew in the asteroid
  belt.
• Lunine et al. ran simulations where terrestrial
  planets are formed from Mercury-to-Mars-mass
  planetary embryos ranging in position from .5-4
  AU.
• Simulations in gas-free environment form massive
  planets.
• Inclusion of gas forms a number of very small
  planets.
• This doesnt indicate failure of the model, but
  the stochastic (random) nature of terrestrial
  planetary formation.

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Origin of Water on Mars (2)

• Lunine et al. conclude that
• Mars is an embryo that escaped ejection by
  Jupiter or accretion of growing terrestrial
  planets.
• Mars did not acquire its water from collisions
  with planet-sized embryos like Earth.
• Mars collided with populations of comets and
  small asteroids and retained most of the water
  acquired from these collisions.

Collisional history of water-laden asteroids with
Mars expressed as cumulative fraction of C-type
asteroids accreted vs. time (Ma)
Probability of cometary collisions with Mars as a
function of their initial semi-major axes
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Climate Conditions

• Abe, Y. and Abe-Ouchi, A. 2 discuss
• There are three climate regimes on a land planet,
  they depend on the obliquity and average surface
  temperature.
• The frozen regime is completely frozen and there
  is essentially no transport of water occurring,
  with a very low surface temperature due to high
  albedo.
• The upright regime occurs when the obliquity of
  the planet is smaller than the width of the
  Hadley cell and the summer temperature exceeds
  freezing temperature. The low-latitude area is
  always warmer than mid to high latitude area.
• The oblique regime occurs when the obliquity of
  the planet is greater than the width of the
  Hadley cell and the summer temperature is above
  freezing point. The mid to high latitude area is
  always warmer than the low-latitude area.

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Climate Conditions (2)

• Mars is believed to have experienced a large
  change in obliquity, as much as 60.
• Abe, Y. and Abe-Ouchi, A. 2 ran simulations for
  land and aqua planets with obliquities of 0 and
  23.5 (upright regime) and 45 and 60 (oblique
  regime).
• They conclude that a land planet has a stronger
  resistance to complete freezing than an aqua
  planet.
• Both land and aqua planets in the oblique regime
  show stronger resistance to complete freezing
  than an upright planet.
• Also conclude that on a land planet in an oblique
  regime, low latitude area is more susceptible to
  freezing than mid-latitude area.

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Evidence of an Ocean

• Parker et al. 4 discuss
• Standing water forms an equipotential surface
  that intersects topography at fixed elevation
  around the margin of a depression.
• Abandoned shorelines are seldom level, though
  they often approximate a planar surface that has
  been tilted, faulted, or warped due to structural
  changes, isostatic rebound, or loading.
• Head et al. 3 point out that
• Large outflow channels empty into the northern
  lowlands.
• Data from the Mars Orbiter Laser Altimeter (MOLA)
  instrument shows the unusual smoothness and and
  flatness of the northern lowlands.

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Evidence of an Ocean (2)

• Parker mapped two contacts that are generally
  parallel to the southern boundary of the northern
  lowlands, which are interpreted to be ancient
  shorelines.

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Evidence of an Ocean (3)

• Contact 2 is a better approximation to a straight
  line. The elevation range is 4.7 km, with a mean
  value of -3.760 km and a standard deviation of
  0.560 km.
• The most substantial variations occur in Elysium
  and Arabia where post-contact 2 activity has
  occurred, and near Tharsis, where uplift could
  have occurred.

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Evidence of an Ocean (4)

• Parker and Banerdt 6 discuss the Mars Orbiter
  Camera (MOC) image at left as a pair of terraces
  winding around the inside rim and knobs with a
  large, degraded crater in northern Arabia Terra
  at the lowland/upland boundary. This is just one
  example of a shoreline they found.
• They conclude that Martian features exhibit a
  wide range of preservation states, suggesting
  geologic timescales.
• They also conclude that the shorelines suggest
  the involvement of water, and little/no evidence
  of fluvial or glacial scour.

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Evidence of an Ocean (5)

• Head et al. 3 use the northern hemisphere
  topographic map to assess what would happen if
• individual channels emptied into the lowlands at
  different times and proceeded to fill them,
• they were filled by a different mechanism (for
  the case of an ancient ocean that is older than
  outflow channels), and
• if such an ocean were to recede.
• They flood the northern lowlands and observed
  where water would pond, and how the oceans might
  evolve with changing depth.

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Flood depth of 1000 m
Flood depth of 500 m
Flood depth of 1490m (contact 1)
Flood depth of1680 m, (mean depth of contact 1,
level of contact 2 shown underneath)
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Bimodal Distribution Similarity
Smith et al. Science 1999
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Conclusions

• Water was brought to Mars by cometary and small
  asteroid impacts and was able to retain most of
  the water.
• It is possible that the climate could have
  supported liquid water at mid latitudes.
• Contact 2 forms an equipotential that could
  represent ancient shorelines.
• Mars probably had an ocean some time in its past!

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References

• 1 Lunine, J. et. al., The origin of water on
  Mars, Icarus, 165(1)1-8, 2003.
• 2 Abe, Y. and Abe-Ouchi, A. (2003) 34th Annual
  Lunar and Planetary Science Conference, Abstract
  1617.
• 3 Head, J. et al., Possible ancient oceans on
  Mars Evidence from Mars Orbiter Laser Altimeter
  Data, Science, 2862134-2137, 1999.
• 4 Parker, T.J. et al., (2001) 32th Annual Lunar
  and Planetary Science Conference, Abstract 2051.
• 5 Parker, T.J. et al., (2002) 33th Annual Lunar
  and Planetary Science Conference, Abstract 2027.
• 6 Parker, T.J. and Banerdt W.B., (1999),
  International Conference on Mars 5, Abstract
  6114.