Leathery vs. Smooth Surface
December 8, 2012
Today's featured image displays a portion of Mons Bradley (highland materials), about 150 km southwest of the Apollo 15 landing site. The southern half of this image has a leathery, rough texture, while the northern half shows a relatively smooth surface peppered with small impact craters. The leathery texture occurs on the northern slope of Mons Bradley, and makes a gradual transition to the smoother surface instead of an abrupt contact. What is the origin of these two contrasting surfaces? The upper smoother area may be an old ejecta blanket covering a pre-existing leathery surface. In that case, the smooth area is younger. If so, why are there more craters on the smooth surface? The surface regolith (unconsolidated rock debris comprising the first few meters of most of the lunar suface) might have been removed in the southern area, taking its store of impact features along with it. But what mechanism could remove regolith over such a broad area? Lunar Orbiter Laser Altimeter (LOLA) data reveal an almost uniform slope all the way down from the top of Mons Bradley until this leather/smooth texture boundary, at which point the slope then shallows. This may be suggesting that the origin of the leathery texture is disturbed regolith - perhaps the result of slow creep down the Mons Bradley slope. In this case, the leathery surface would be younger than the smoother surface. What other clues could be looked for to explain the origins, and determine the relative age, of these interesting rock units? Leathery surface at Mons Bradley. Image number M116309931R, scale 0.73 m/pixel, image width 876m, incidence angle 84°, sunlight is from southwest [NASA/GSFC/Arizona State University].
Topics: Planetary geology, Geology, Planetary science, Hadley–Apennine, Regolith, Geomorphology, Sedimentology, Astronomy, Moon