Comparing Martian Ice Depths

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Comparing Martian Ice Depths

• by Roozbeh Akhtari, Lucas Allen-Williams,
  Katherine Pearl, and Michael Reed

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Question

• Is the depth of ice underneath the surface of
  Mars in two areas similar in latitude
  (equatorial) and altitude (low) different?
• The depth of ice in these areas is important
  because it tells us about Marss geological past
  and can give us hints towards finding past or
  present life on Mars.

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Rampart Craters

• Occur when meteorite strikes an area with
  underground ice or water that is shallow enough
  to affect the crater.
• On Mars, we assume that what causes the rampart
  craters is ice.
• The impact melts the ice, which forms a muddy
  slurry.
• Slurry flows outwards from the crater.
• When slurry stops, it creates a tall, bluff-like
  edge.

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Mars and Water

• Much evidence that a large amount of liquid water
  once existed on the surface of Mars.
• The existence of large channels points to
  catastrophic floods that at one time released
  large amounts of water.
• There remains the question of what happened to
  all the water, besides the water in the polar ice
  caps.
• Many people think that the water is now in ice
  beneath the surface.
• Older research says that ice is about 200m below
  the surface near the equator, and shallower the
  closer one gets to the poles.

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New Research

• Recent evidence shows that there may be ice much
  closer to the surface in equatorial regions that
  previously believed
• Research with pack-ice and rampart craters finds
  volatiles 20-60m below the surface
• If volatiles were ice, they probably would not
  disappear without leaving evidence of change.
• Change not found, leading researchers to believe
  that there may be significant shallow ice
  reservoirs in these areas
• There also may be liquid water with the ice

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Chryse Planitia 24 craters measured Elysium
Planitia 22 craters measured
Elysium Planitia
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Diameter in meters rim to rim
-Diameter is obtained by measuring craters using
THEMIS imaging data -Depth is obtained by
measuring craters using MOLA imaging data -By
comparing depth and diameter of rampart craters
and non-rampart craters, we can determine the
depth to ice -By looking at a non-rampart crater,
we can find a minimum ice depth for the time and
location of that specific crater
Depth in meters rim to bottom
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Finding the diameter of a crater

• Find a THEMIS image of the crater
• Open image in Canvas
• Set pixel aspect ratio to the resolution of the
  THEMIS image
• -Draw a line across the diameter of the crater
  from one rim to the other
• -Measure the line using the object specs feature

9424 m
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Finding the depth of a crater
-Find the crater in Gridview using the MOLA
data -Take a profile of the crater -To find the
depth, measure the difference between the highest
point of the rim and the lowest point on the
bottom of the crater
-1475
925 m
-2400
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RESULTS
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Superimposed Graphs of Chryse Planitia and
Elysium Planitia
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What Does This Show?

• The average crater depths for both Chryse
  Planitia and Elysium Planitia are relatively
  equal and consistent, although there is variation
  within each group.
• Virtually all of the crater depths are larger
  than the global trendline values.
• Overlapping diameter / depth zones of rampart and
  non-rampart craters ? variation in ice depth over
  time?

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Possible Explanations for Unusual Depth of Craters

• 1)Global trendline craters are old and filled in
  with sediment
• 2)Our craters were from ice-rich areas ? weaker ?
  impacts blew out more material
• Consequences of Explanations
• 1) Ice-influence ? cant use global predictions
• 2) Fill-in ? can use global ice-depth predictions
  because their craters formed similarly to ours
• Ways to test
• We observed pack ice formations in Western
  Chryse Planitia, and hypothesize that the ice
  should be shallower there. If that is true, then
  there should be more of an ice-influenced depth
  effect there. This is the Geographic Variation
  test.
• Look at unusually deep and unusually shallow
  craters and look for evidence of erosion or
  sediment deposition.

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Geographic Variation?

• Is the difference from the global trendline
  uniform?
• Used Latitude Longitude
• R-squared value shows how big of an effect the
  latitude or longitude had on depth.

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Is Everywhere in Elysium Planitia the Same?
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How about in Chryse Planitia?
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Location-Depth Relationship

• Total R-squared for each approx. 20 ?
  geography has a small effect, but its far from
  complete
• Craters relatively deeper in Eastern Elysium
  Planitia and Northern Chryse Planitia
• Chryse Planitia results are not the expected
  results ? no evidence for ice influencing crater
  depth
• Somewhat small R-squared ? its not too bad an
  approximation to say that each sample is
  internally uniform

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Are the craters filled in?

• A look at some of the craters with the highest
  and lowest deviation from the expected depth says
  yes
• Looked at the shallowest and deepest craters from
  Elysium Planitia (EP) and Chryse Planitia (CP)

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EP Crater 22 is unusually shallow
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as is CP Crater 10
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While EP Crater 3 is unusually deep...
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However, CP Crater 3 is also unusually deep
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Sediment Fill Seems Likely

• Shallower ? filled in (old)
• Deeper ? fresh (new)
• Hypothesis our craters are fresher than the
  national average, which is why they are deep.
• We dont have evidence for ice influencing the
  crater explosion, but the rampart crater
  morphology group (see Pomona Geology website) has
  looked into it and found some.

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Conclusions

• Assuming fill-in is the only factor changing our
  results, we can use a global ice depth prediction
  (using diameter, which should not be changed by
  sediment fill)
• Bounds on ice depth variation over time (smallest
  rampart craters to largest non-rampart craters)
• CP Ice was as shallow as 46 m at one point and
  as deep as 60 m at another
• EP Ice was as shallow as 74 m and as deep as 123
  m at another
• These bounds do not intersect, so the two
  locations are significantly different.
• Ice was about 2x as deep at Elysium Planitia!

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THE END

• The answer to our question is, to put it simply,
• Yes.
• Sources
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