Volcanic structures within Niger and Dao Valles, Mars, and implications for outflow channel evolution and Hellas Basin rim development

Abstract Outflow channel formation on the eastern Hellas rim region is traditionally thought to have been triggered by activity phases of the nearby volcanoes Hadriacus and Tyrrhenus Montes: As a result of volcanic heating subsurface volatiles were mobilized. It is, however, under debate, whether eastern Hellas volcanism was in fact more extensive, and if there were volcanic centers separate from the identified central volcanoes. This work describes previously unrecognized structures in the Niger‐Dao Valles outflow channel complex. We interpret them as volcanic edifices: cones, a shield, and a caldera. The structures provide evidence of an additional volcanic center within the valles and indicate volcanic activity both prior to and following the formation of the outflow events. They expand the extent, type, and duration of volcanic activity in the Circum‐Hellas Volcanic Province and provide new information on interaction between volcanism and fluvial activity

Target selection for the High Resolution Stereo Camera (HRSC) on the ESA Mars Express mission

The High Resolution Camera (HRSC) onboard the European ESA Mars Express (MEX) mission will map> 50% of the Martian surface in stereo and colour with a resolution of <= 15 m/pixel. In order to optimise the scientific return of the instrument, the preparation of a detailed list of surface targets and their specific scientific interest together with ancilliary information is mandatory. We describe the organisation of the list of > 1400 individual targets, the parameter specified for each target, and how the list will be used in operations planning. Finally, we outline possible further applications of the list for upcoming Mars missions like the Mars Reconnaissance Orbiter

Polygonal impact craters in Argyre region, Mars: Implications for geology and cratering mechanics

Impact craters are not always circular; sometimes their rims are composed of several straight segments. Such polygonal impact craters (PICs) are controlled by pre-existing target structures, mainly faults or other similar planes of weakness. In the Argyre region, Mars, PICs comprise ~17% of the total impact crater population (>7 km in diameter), and PICs are relatively more common in older geologic units. Their formation is mainly controlled by radial fractures induced by the Argyre and Ladon impact basins, and to a lesser extent by the basin-concentric fractures. Also basin-induced conjugate shear fractures may play a role. Unlike the PICs, ridges and graben in the Argyre region are mostly controlled by Tharsis-induced tectonism, with the ridges being concentric and graben radial to Tharsis. Therefore, the PICs primarily reflect an old impact basin-centered tectonic pattern, whereas Tharsis-centered tectonism responsible for the graben and the ridges has only minor influence on the PIC rim orientations. According to current models of PIC formation, complex PICs should form through a different mechanism than simple PICs, leading to different orientations of straight rim segments. However, when simple and complex PICs from same areas are studied, no statistically significant difference can be observed. Hence, in addition to enhanced excavation parallel to the strike of fractures (simple craters) and slumping along the fracture planes (complex craters), we propose a third mechanism involving thrusting along the fracture planes. This model is applicable to both simple and small complex craters in targets with some dominating orientations of structural weakness.The Meteoritics & Planetary Science archives are made available by the Meteoritical Society and the University of Arizona Libraries. Contact [email protected] for further information.Migrated from OJS platform February 202

Alluvial Fan in Icaria Planum, Mars

The Mars Express HRSC data were used to study fluvial history of southern Claritas on Mars. Volatiles, transported downslope to the basin, breached through a saddle valley and formed a channel towards Icaria Planum in the west. Along the channel, sapping provided additional water. The channel broke into a 30-km impact crater and formed a temporary lake. The crater rim has terraces and the floor has smooth deposits. A delta was formed in a standing water. After breaching the crater rim through a neck which is higher than the crater floor, water deposited onto Icaria Planum an alluvial fan. This fan was studied using the HRSC colour data by mapping deposit units of the Icaria lowlands in front of the channel. The flood deposits were made visible by the multichannel HRSC data classification. The alluvial structures reflect topography and regional slopes as well as the amount of available water. The hi-resolution HRSC image provides an additional view into the alluvial structures, erosion and sedimentation in the channel formation. These remote sensing approaches facilitate the mapping of characteristic phases in the fluvial development of the area studied