Aeolian Features in Martian Craters

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Aeolian Features in Martian Craters

• By Diana Batres, Bradley Markle, Brian Morrison,
  Nikolay Nikolov, and Michael Powell

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Our Question

• How do the topographic features on Mars affect
  the morphologies and characteristics of the dune
  fields that form in and around them?

Photo taken by Mars Opportunity Rover
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Dunes on Mars An Overview

• Martian dunes were first discovered in Viking
  photos from the 1960s and 1970s.
• Further study has revealed that dunes commonly
  form in craters and canyons.
• Dune fields in craters are mainly transverse,
  suggesting largely unidirectional wind patterns.
• Many different types of dunes can be found in
  Northern Plains and really remarkable formations
  have been observed near the poles.

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An Introduction to Sand Dunes

• Sand dunes formed by unidirectional winds have
  two distinct faces a gentle windward face and a
  steeper slip face.
• Wavelength, in dune fields, are measured between
  peaks of adjacent dunes.

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An Introduction to Dunes
Barchan Dunes

• All the dunes in our study are of the
  barchanoid type (as classified by McKee
  (1979)).
• We saw the three main subtypes of theses dunes
  Barchan dunes, Barchanoid ridges, and transverse
  dunes. All of these subtypes have axes
  perpendicular to wind direction.
• We were able to measure the wavelengths in
  transverse dune and barchanoid ridge fields.
• Note the gradation between subtypes.

Barchanoid Ridges
Transverse Dunes
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Why Study Dune Fields in Craters?

• Sand dunes are well preserved in low-lying areas.
• It is difficult for sand grains to be lifted up
  from a depression once they have been trapped.
• Crater walls create a shelter from the wind,
  allowing undisturbed dune formation.
• Thus, crater bottoms are a prime location to
  study dune fields!

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Purpose

• Our Goal
• To determine if crater elevation, depth, size,
  floor slope, and/or location influence dune
  wavelength on Mars.

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Significance?

• It is important to understand Aeolian processes
  on Mars.
• Understanding trends in dune formation is
  essential to future Mars projects.

• This knowledge will help us in finding ideal
  landing and building sites
• The Opportunity Mars Rover is currently stuck in
  a sand dune in a crater.
• The Spirit Rover is
• currently in Gusev
• crater, which we
• studied during this
• project.

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The THEMIS and MOLA Instruments

• The THEMIS images and the MOLA data have shown
• these dunes in a unprecedented level of detail.
• The THEMIS camera takes both visual and IR images
  with very high resolution.
• Data from the Mars Orbiter Laser Altimeter (MOLA)
  has been used to assemble a complete topographic
  profile for all of Mars.

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Experiment DescriptionStep 1

• We researched likely locations for dune fields
  within craters.
• Using the extensive THEMIS images database, we
  found and located visible images of over 11
  different craters containing usable dune fields.

1km
Kaiser Crater
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THEMIS Targeting and Images Gathered

• Using JMARS, we targeted two possible sites for
  our THEMIS images. The target above was of three
  never-photographed craters.

• This is one of the two images we received from
  ASU.

• Upon close examination, we found a small dune
  field in the central crater.

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Experiment Description

• We measured individual dune wavelength and
  distances from edge of dune field using Canvas
  8.0.
• Specifically, we imported each THEMIS image into
  Canvas
• Then set the resolution appropriately
• And measured the wavelength of each dune using
  the line tool.
• Where appropriate, we also measured the distance
  from each dune (where we took a wavelength
  measurement) to the edge of the field in a
  similar fashion using the line tool.

1 km
1km
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Experiment Description

• We used the MOLA data set and GridView to find
• Crater depth
• Crater diameter
• Surface slope (when present)
• Average crater floor elevation

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Analysis

• We compiled data taken from past THEMIS images,
  our new image, and MOLA into a spread sheet.
• We created graphs based on this data to plot dune
  wavelength against our different experimental
  variables.
• We looked for trends in these graphs that could
  provide insights into dune formation.

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ResultsCorrelation with Crater Diameter?

• Definite trend between Diameter and Wavelength.
• Possible correlation.
• Fairly linear, and a pretty strong R2 value.

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Correlation with Crater Depth?

• There is no real trend observed here. This is an
  essentially even distribution.

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Correlation with Crater Elevation?

• Here we see a vague trend but nothing very
  definitive.
• There is a greater probability of longer
  wavelengths at elevations closer to 0 km.

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Correlation with Crater Location?Latitude

• Possible correlation between Latitude and
  Wavelength generally found shorter wavelengths
  near equator.
• Differences between Northern/Southern hemispheres
  of Mars?
• Insight to wind patterns near equator?
• If one was going to find a correlation with
  latitude, one might expect a curve similar to
  this.

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Correlation with crater location?Longitude

• We could find no simple or plausible correlation
  between longitude and wavelength.

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Correlation between Dune Wavelength and Distance
from Crater Edge?

• Strong proportional relationship between distance
  from edge of field and wavelength.
• Possible explanation interior of fields contain
  more sand with which to make bigger dunes.
• Should note that many fields never showed this
  relationship.

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Conclusions

• We found a strong correlation between the
  diameter of the crater and the dune field
  wavelength. As crater diameter increases,
  wavelength increases fairly linearly.

• Possible reasons for trend/correlation
• Diameter affects wind patterns over crater
• Larger diameter allows for greater surface area
  to be affected
• by wind
• Allows for greater sand deposition
• Allows for larger dunes to be formed

• Our data suggests NO correlation between crater
  depth and dune field wavelength.
• This is somewhat interesting especially
  considering our findings regarding crater
  diameter.

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Conclusions Continued

• There seems to be some correlation to elevation
  and dune wavelength.
• Our data shows that there is a greater
  possibility for larger wavelengths at elevations
  closer to mars mean.
• Why? Perhaps this suggests wind patterns in areas
  with elevation closer to mean vary more than at
  other elevations, giving rise to more variety of
  wavelengths (including longer ones). At any rate,
  it is certainly a complicated relationship.

• We found a pretty strong correlation between
  latitude and wavelength, generally finding
  shorter wavelengths closer to the equator.
• This may suggest something globally about the
  wind patterns that shape these dunes in areas
  nearer the equator. This is rather reasonable. On
  Earth we find that global wind patterns exhibit
  latitude dependence. Specifically near the
  equator there is somewhat of a dead zone.

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Conclusions Concluded

• We found no observable correlation between
  longitude and dune wavelength.
• This is not surprising.
• We found no correlation between crater floor
  slope and dune wavelength at all.
• We found strong correlations between the
  wavelength and distance that wavelength was from
  the edge of the dune field. As that distance
  increased so did the wavelength.
• This can be explained by the fact that the
  interiors of larger dune fields contain more
  sand, and that larger dunes with larger
  wavelengths require more sand than smaller dunes.
• We also found that in at least one case the dune
  field seemed to have a maximum wavelength of
  around 2 km.
• It is interesting that some fields exhibited this
  variance while others did not. Whether or not a
  field showed this seemed only to depend on field
  size and not on any of the craters
  characteristics.