Peculiar texture of high-latitude ground-ice-rich terrains M. A. Kreslavsky and J. W. Head Brown University Kharkov Astronomical Institute

Kreslavsky and Head 2000: Smoothing at high latitudes ( MOLA data ) + + Mantling ( MOC images )   High-latitude deposits Malin and Edgett 2001: MOC images  High-latitude young mantle Mustard et al. 2001: Dissection in  latitude zones ( MOC images )   Ice-rich deposits Kreslavsky and Head 2002: Synthesis:  Ice-rich high-latitude mantle Tokar et al. 2002: Merging with GRS/NS/HEND data

E02/ W 61 N 500 m MOC NA image

High-Latitude Mantle: Morphology very smooth (10s-100s m scale) characteristic texture (10 m scale) –affected by topography (100s m - km scale) –affected by latitude very homogeneous a few meters thick layered structure mechanically strong eroded at steep slopes dissected / eroded at lower latitudes (<60˚)

Typical mantle textures 1 km “basketball” wrinkle regular polygonal

Latitudinal distribution of mantle textures

E04/ W 69 N 1 km MOC NA image

E04/ W 69 N 1 km MOC NA image

E04/ W 69 N 1 km MOC NA image

E04/ W 69 N 1 km MOC NA image

M02/ m 150 W 69 N MOC NA image

M02/ m 150 W 69 N MOC NA image

High-Latitude Mantle: Morphology very smooth (10s-100s m scale) characteristic texture (10 m scale) –affected by topography (100s m - km scale) –affected by latitude very homogeneous a few meters thick layered structure eroded at steep slopes dissected / eroded at lower latitudes (<60˚) mechanically strong

E02/ W 74 N 500 m MOC NA image

High-Latitude Mantle: Icy HEND / NS / GRS data –high ice content at depth (1 m scale) –low ice content near the surface Has mechanical strength Extent agrees with subsurface ice stability Erosion: - on steep slopes - at low latitudes Analogy with patterned ground in terrestrial permafrost regions High-Latitude Mantle: Indurated No erosion of the ice-free upper layer

E02/ W 79 N 500 m MOC NA image

E02/ W 60 N 1 km MOC NA image

E02/ W 51 N 1 km E02/ W 65 N

Latitudinal distribution of pits and craters

High-Latitude Mantle: Crater Retention Age Malower latitudes <0.1 Mahigher latitudes Crater retention age uncertainty: –rescaling of cratering rate from lunar record –extrapolation for younger ages –poor statistics –unknown atmospheric shielding Crater retention age difference: –deposition age difference –persisting protecting ice sheet

High-Latitude Mantle: Mechanism of Formation Deposition of ice and dust + desiccation and induration of upper layer Latest periods of high obliquity –water vapor availability and mobility –dust lifting –extended subsurface ice stability zones Latest volcanic and/or water outflow episode

“Astronomical” climate forcing

Mantle deposition: NOT now NOT the last 0.4 Ma

The most recent mantle deposition: 30° 0.4 Ma ? 34° 0.6 Ma ? 40° 4.1 Ma ? 45° > 5 Ma ?

Conclusions Detected by HEND high H concentration at high latitudes is due to specific deposit: ice-rich mantle The mantle is geologically young ( Ma ?) Complex history of deposition - alteration - removal