Latitudinal Trend of Roughness and Circumpolar Mantles on Mars

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Latitudinal Trend of Roughnessand Circumpolar
Mantles on Mars

• M. A. Kreslavsky
• J. W. Head III
• Brown University

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Statistical characterization of kilometer-scale
topography with MGS MOLA data

• M. A. Kreslavsky, J. W. Head (2000)
• JGR-Planets, v. 105, no. E11, p. 26,695 - 26,711
• some new results

• MOLA - measurements of the surface elevation
• 600 000 000 shots
• 0.3 km shot-to-shot distance along track
• up to 1.5 km gaps between tracks
• up to 0.3 m vertical precision
• up to 3 m vertical accuracy

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d characterizes profile curvatureat given
pointat given baseline. We calculated d for
each shotand binned into map cells Map
grid 8x8 cells per degree. Typically 40-80
shots per map cell
Baselines used 0.6 km 2.4 km 9.6 km
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Curvature-frequency distributiona statistical
characteristic of topographic pattern
For each map cellwe calculated interquartile
widthof the distribution. It characterizesrough
ness at given baselinefor given map cell. All
map cells form a roughness mapfor each
baseline We combined 3 maps for 3 baselines
into one color map
Baselines used 0.6 km 2.4 km 9.6 km
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Roughness map
Blue 0.6 km baseline Green 2.4 km
baseline Red 9.6 km baseline
Brighter Rougher
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Roughness map

• Olympus Mons Aureole very rough
• Amazonis and Elysium Planitia very smooth
• Dune fields rough at small scale, flat in large
  scale
• Polar caps smooth at small scale steep
  larger-scale slopes
• Volcanic plains are smoother than highlands
• Northern lowlands are rather smooth and have
  characteristic 3-km-scale roughness

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Latitudinal trend of roughness

• S hemisphere
• highlands at low latitudes are rougher (30N -
  30S)
• highlands at high latitude are smoother (gt60S)
• at 0.6 km baseline
• N hemisphere
• Similar trend partly masked with the dichotomy
  boundary and other intrinsic roughness contrasts.
• Interpretation that survived tests with
  high-resolution MGS MOC images Manifestation of
  unique type of surface mantle depositswith
  specific meter-scale texture

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MGS MOC image M03/04333
The deposits with specific fine texture
(center)are superposed over underlying
topography at 47N in Utopia Planitia
500 m
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MGS MOC image M23/01695
Dark dunes travel over the deposits with
specific texture at 75N and leave no
traces. The deposits are strong, probably
cemented
500 m
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MGS MOC image M02/01316
The deposits with specific texture show complex
stratigraphy.The uppermost layer 4 m thick is
removed in some places. Circular features are
impact craters of cratered cones, degraded and
mantled.
500 m
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High-latitude surface mantle deposits

• Very likely cemented by water ice
• May be desiccated at lower latitudes (30-60)
  (Mustard et al., 2001)
• Currently undergoing slow degradation at margins
  (?) (Mustard et al., 2001)
• gt 1-3 m thick ( lt roughness signature)
• 3 m thick at margins ( lt MOC images, Mustard et
  al., 2001)

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High-latitude surface mantle deposits

• Diverse morphology
• Complex stratigraphy
• History of successive deposition and removal
• Persisted through at least Late Amazonian
• Undergo changes during obliquity cycles
• A range of processes operating ( lt MOC
  high-resolution images)