A Map of Kilometer-Scale Topographic Roughness of Mercury

Abstract:

We present a new map of the multiscale topographic roughness of the northern circumpolar area of Mercury. The map utilizes high internal vertical precision surface ranging by the laser altimeter MLA onboard MESSENGER mission to Mercury. This map is analogous to global roughness maps that had been created by M.A.K. with collaborators for Mars (MOLA data) and the Moon (LOLA data). As measures of roughness, we used the interquartile range of along-track profile curvature at three baselines: 0.7 km, 2.8 km, and 11 km. Unlike in the cases of LOLA data for the Moon, and MOLA data for Mars, the MLA data allow high-quality roughness mapping only for a small part of the surface of the planet: the map covers 65N - 84N latitude zone, where the density of MLA data is the highest. The map captures the regional variations of the typical background topographic texture of the surface. The map shows the clear dichotomy between smooth northern plains and rougher cratered terrains. The lowered contrast of this dichotomy at the shortest (0.7 km) baseline indicates that regolith on Mercury is thicker and/or gardening processes are more intensive in comparison to the Moon, approximately by a factor of three. The map reveals sharp roughness contrasts within northern plains of Mercury that we interpret as geologic boundaries of volcanic plains of different age. In particular, the map suggests a younger volcanic plains unit inside Goethe basin and inside another unnamed stealth basin. -- Acknowledgement: Work on data processing was carried out at MIIGAiK by MAK, AAK, NAK and supported by Russian Science Foundation project 14-22-00197.