地形学からみた火星における過去から現在までの水成活動

Abstract

This paper overviews water sculpted Martian landscapes, ancient through to possibly present day, which have become more pronounced through each new orbiting, landing, and roving mission. Geomorphological evidence of ancient aqueous activity associated with lakes and putative oceans includes a diversity of features. Features include sedimentary sequences, debris flows, fluvial valleys, alluvial fans, giant polygons, and glacial and periglacial landscapes. Arguably one of the most significant geomorphological indicators of a paleoocean is deltaic landforms identified along a topographic zonal boundary which correlates with reported putative shorelines. Other evidence includes distinct geochemical/mineralogical/elemental signatures of aqueous weathering. In addition, relatively high-resolution imaging cameras onboard the Mars Global Surveyor, Mars Odyssey, and Mars Reconnaissance Orbiter have detailed features which indicate recent and possibly present-day aqueous activity such as slope streaks, slope linea, gullies which occur along faults and fractures and source from geologic contacts and tectonic structures, and possible open-system pingos, among other feature types. Ancient, recent, and possibly present-day features point to both surface and subsurface aqueous environments throughout time, and thus making Mars a prime target to address the everimportant question of whether life exists beyond the Earth.