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Abstract: We present new insights into possible formation mechanisms and implications for previously identified landforms of putative glacio-fluvial origin along the southern rim of the Argyre basin on Mars. We compiled a detailed geomorphologic map of the study area and conducted morphometric and stratigraphic analyses of specific features, e.g., esker-like sinuous ridges on layered terrain. Based on their morphology and orientations, we subdivided the sinuous ridges on the southern Argyre basin floor into two populations, which could reflect changing conditions of glacial retreat. With the transition and oblique path methods we quantified the ice thickness of the glacier under which the first, lesser degraded, population of ridges probably formed. Our results imply an ice sheet thickness of ~2km and at least ~100,000–150,000km³ of ice on the southern floor of the Argyre basin during the time those ridges were deposited (>30× the volume of Vatnajökull, Iceland). The second population of ridges is more degraded and shows layers occasionally extending into the surrounding layered terrain. Comparisons with the morphology surrounding the Piedmont-style Malaspina Glacier in Alaska show similarities, suggesting population II formed during a glacial retreat involving back- and downwasting of stagnant ice lying beneath fresh outwash sediments, creating degraded and layered lag deposits around the emerging eskers. If outwash sediments were fed by the same drainage source as the eskers, sections of layers can extend from a given ridge into the surrounding deposits. The differences between the two ridge populations are probably a result of the subglacial drainage direction changing from northward to north-eastward around 3.6Ga ago. This was likely coupled with the deposition of less or no outwash sediments resulting in a decrease of lag deposits. A subsequent phase of stagnant glacial retreat left no terminal moraines and largely preserved the population I ridges, thus implying sufficient glacial thinning in order for the ice flow to stop. This, in turn, may have been caused either by sublimation in a cold but increasingly dry climate, or by melting and increased glacier surface runoff due to rising temperatures. [Copyright &y& Elsevier]

Abstract: The observation of gullies on Mars raised questions about the presence of liquid water in the recent past. In some regions like Hale and Bond crater, gullies occur in one crater (Hale) but do not in another crater nearby (Bond). These regional differences have been interpreted as an argument for a formation of the gullies related to groundwater. The formation of gullies on Earth depends on rainfall and/or melting of snow as well as on several parameters such as the presence of steep slopes and sufficient amounts of fines and debris. We investigated the Hale/Bond region for differences in crater wall morphology and texture, slopes, and thermal properties to determine whether the gully formation is dependent on factors such as steep slope angles and availability of fine-grained material. Morphologically there exist two kinds of gullies in the Hale crater: Gullies on the south- and east-facing crater slopes have a pristine appearance with deep channels eroded into the talus material and well-preserved aprons. Gully-like features on the north- and west-facing slopes are degraded and superposed by craters, indicating that they are old in comparison to the pristine ones. However, their formation process is unclear and might be due to debris flows, surface runoff or dry mass wasting processes or a combination of these processes. The crater walls of Bond do not show gullies. Their morphology is most likely consistent with a degraded mantle deposit. Slope measurements reveal that the gullies in Hale crater occur on slopes between ∼20° and ∼30° in contrast to the slopes without gullies in Bond that are between ∼10° and ∼20° steep. Mean thermal inertia values on slopes with younger gullies are ∼175Jm−2 K−1 s−1/2 corresponding to higher amounts of fine-grained material. At slopes with older gully-like features mean thermal inertia values are ∼315Jm−2 K−1 s−1/2 corresponding to higher amounts of bedrock or possibly indurated grain sizes. Mean thermal inertia values of the Bond crater walls are ∼230Jm−2 K−1 s−1/2 indicating more consolidated terrain possibly due to the cementation of the dissected mantle material. From our investigation we conclude that the occurrence of gullies in the Hale/Bond region most likely depends on the distribution of unconsolidated material and steep slopes. The regional and local gully distribution on Mars likely varies due to differences in topography and surface material properties. Their proposed clustered distribution on Mars is not an argument for a groundwater formation mechanism of the gullies. [Copyright &y& Elsevier]

Images of Mars taken by spacecraft in the last few decades indicate that the landscape has changed and that current processes are continuously changing the surface. The modifications of the landscape are caused by exogenic processes including eolian activity, mass movement, the growth and retreat of the polar caps, glacial processes and crater-forming impacts. In particular the High Resolution Stereo Camera (HRSC) on board Mars Express (MEx) and the Context Camera (CTX) on board the Mars Reconnaissance Orbiter (MRO) cover large areas at high resolution and thus are particularly well-suited to detect the extent and origin of surface changes on Mars. Multi-temporal observations of variable features on Mars became possible by the increasing number of repeated image acquisitions of the same surface areas. To support the investigation of surface changes that represents a key element in martian research, we developed MUTED, the “Multi-Temporal Database of Planetary Image Data”, which is a tool for the identification of the spatial and multi-temporal coverage of planetary image data from Mars. Using MUTED, scientists are able to identify the location, number, and time range of acquisitions of overlapping images from, for example, HRSC and CTX. MUTED also includes images from other planetary datasets such as those of the Mars Orbiter Camera (MOC), the Thermal Emission Imaging System (THEMIS), and the High Resolution Imaging Science Experiment (HiRISE). The database supports the identification and analysis of surface changes and short-lived surface processes on Mars based on fast automatic planetary image database queries. From the multi-temporal planetary image database and investigations based on multi-temporal observations we will better understand the interactions between the surface of Mars and external forces, including the atmosphere. MUTED is available for the planetary scientific community via the webpage of the Institut für Planetologie (IfP) Muenster. [ABSTRACT FROM AUTHOR]

Abstract: “Dendritic valley networks” and broad “longitudinal valleys” are widespread within the eastern Libya Montes region. The morphologic characteristics of the studied dendritic valleys, especially their occurrence at local summits, provide evidence for the initial formation by surface runoff due to atmospheric precipitation whereas the longitudinal valley systems are thought to have been formed and modified by groundwater-induced processes. Our crater counts and model ages show, that the dendritic valley networks (average age ∼4.0 Ga) formed earlier than the longitudinal valley systems (average age ∼3.7 Ga). Both fluvial forms indicate a temporal change of the erosive environment at the Noachian/Hesperian transition at ∼3.8 Ga. Our results suggest that the fluvial activity within our investigation area lasted for ∼800 My, from ∼4.1 Ga to ∼3.3 Ga. The dendritic valleys show valley densities between 0.12 km−1 and 0.57 km−1, indicative of highly mature and integrated valley systems that we interpret to be characteristic of warmer and wetter conditions on Mars. [Copyright &y& Elsevier]