latitudinal trend of roughness and circumpolar mantles on mars m. a. kreslavsky j. w. head iii brown...

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)