Kilometer-scale roughness of Mars: Results from MOLA data analysis

The Mars Orbiter Laser Altimeter (MOLA) data are used to characterize the k ilometer-scale surface roughness of Mars. The median absolute value of the differential slope at a given baseline is proposed as a data-derived measur e of the surface roughness at this scale. Study of the scale dependence of roughness for the smoothest terrains gives an independent estimate of 20 cm for MOLA ranging accuracy. The baseline lengths from 0.6 to similar to 20 km are used, and kilometer-scale roughness is mapped for the entire surface . The maps show that different geological units have distinctive roughness characteristics. Scale dependence of roughness for a number of geological u nits is presented and discussed. The southern polar cap is rougher than the northern at kilometer and subkilometer scale, which suggests differences i n the sublimation/condensation balance. The Vastitas Borealis Formation has a distinctive 3-km-scale background surface topography, which suggests a n onvolcanic origin for its upper layer. Young volcanic plains in Amazonis Pl anitia and the eastern part of Elysium Planitia are very similar to each ot her in their roughness characteristics and differ from other volcanic plain s on Mars, which suggests a distinctive eruption style. There are systemati c latitudinal variations of roughness in both the southern highlands and th e northern lowlands: terrains at high latitude are smoother at short baseli nes; the characteristic vertical scale related to this difference is severa l meters. Processes that could be responsible for formation of this trend i nclude creep of ice-rich near-surface material at high latitudes, treatment of the surface with repetitive deposition and sublimation of seasonal fros t, climate-controlled deposition and/or cementation of dust at high latitud es, and repetitive sublimation and accumulation of subsurface ice at low la titudes with climate variations. All mechanisms of origin could operate mor e effectively under different climate conditions. Relevant morphological ob servations favor mechanisms involving deposition of smooth blankets at high latitudes.