Latitudinal Trend of Roughnessand

Circumpolar Mantles on Mars

M. A. Kreslavsky

J. W. Head III

Brown University

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

0 2 4 6

Elevation d

2 . 4 k m

D is t a n c e , k m

baseline

Baselines used: 0.6 km 2.4 km 9.6 km

d characterizes profile curvatureat given pointat given baseline.

We calculated dfor each shotand binned into map cells

Map grid:8x8 cells per degree.

Typically ~40-80 shots per map cell

d

in t e r q u a r t i le

s c a l e

m e d ia n

1/41/41/41/4

q 1/4 q 1/2 q 3/4

Curvature-frequency distribution:a statistical characteristic of topographic pattern

For each map cellwe calculatedinterquartile widthof the distribution.

It characterizesroughness 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

Blue 0.6 km baselineGreen 2.4 km baselineRed 9.6 km baseline

Brighter = Rougher

Roughness map

• Olympus Mons AureoleOlympus 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 highlandsthan highlands• Northern lowlands are rather smooth

and have characteristic 3-km-scale roughness

Roughness map

S hemisphere:

highlands at low latitudes are rougher (30N - 30S)highlands at low latitudes are rougher (30N - 30S)

highlands at high latitude are smoother (>60S)highlands at high latitude are smoother (>60S)

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

Latitudinal trend of roughness

MGS MOC image M03/04333

The deposits with specific fine texture (center)are superposed over underlying topography at 47N in Utopia Planitia

500 m

N

S

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

N

S

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.

N

S

500 m

MGS MOC image M02/01316

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)

• > 1-3 m thick ( <= roughness signature)

• ~3 m thick at margins ( <= MOC images, Mustard et al., 2001)

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 ( <= MOC

high-resolution images)