On the formation fo caldera-like features on Ganymede: implicatoins from Galileo-G28 images

Topographic data are used to find implications for the formation of Caldera-like Features on Ganymede

Amazonian-aged fluvial system and associated ice-related features in Terra Cimmeria, Mars

The Martian climate throughout the Amazonian is widely believed to have been cold and hyper-arid, very similar to the current conditions. However, ubiquitous evidence of aqueous and glacial activity has been recently reported, including channels that can be tens to hundreds of kilometres long, alluvial and fluvial deposits, ice-rich mantles, and glacial and periglacial landforms. Here we study a ∼340 km-long fluvial system located in the Terra Cimmeria region, in the southern mid-latitudes of Mars. The fluvial system is composed of an upstream catchment system with narrow glaciofluvial valleys and remnants of ice-rich deposits. We observe depositional features including fan-shaped deposits, and erosional features such as scour marks and streamlined islands. At the downstream section of this fluvial system is an outflow channel named Kārūn Valles, which displays a unique braided alluvial fan and terminates on the floor of the Ariadnes Colles basin. Our observations point to surface runoff of ice/snow melt as the water source for this fluvial activity. According to our crater size–frequency distribution analysis the entire fluvial system formed during early to middle Amazonian, between ∼1.8+0.2 −0.2 Ga to 510+40 −40 Ma. Hydraulic modelling indicates that the Kārūn Valles and consequently the alluvial fan formation took place in geologically short-term event(s). We conclude that liquid water was present in Terra Cimmeria during the early to middle Amazonian, and that Mars during that time may have undergone several episodic glacial-related events

Small-scale lobes on Mars: Solifluction, thaw and clues to gully formation

The existence of solifluction lobe-like landforms on Mars may, potentially, have important implications for our understanding of the distribution of thaw liquids and its geomorphic effects in recent climate history. In this study we made an inventory of all HiRISE images between 40°S-80°S acquired between 2007 and 2013 and show their distribution and their close spatio-temporal relationship to other ice-related landforms such as gullies and polygons. Based on Earth-analog studies and landscape analysis we conclude that a hypothesis of freeze/thaw may better explain their origin then current ”dry” models

Quantitative Investigations of Polygonal Patterned Ground in Continental Antarctica: A Mars analogue

Polygonal fractured ground is widespread at middle and high latitudes on Mars. The latitude-dependence and the morphologic similarity to terrestrial patterned ground in permafrost regions may indicate a formation as thermal contraction cracks, but the exact formation mechanisms are still unclear. This study quantitatively investigates polygonal networks in icefree parts of continental Antarctica to help distinguishing between different hypotheses of their origin on Mars

Fault scaling at Memnonia Fossae, Mars: Displacement-length relationship derived from HRSC data

Summary Fault population studies are essential to investigate lithospheric strength and stress conditions [1]. Understanding the displacement-length relationship of faults helps us to understand the lithosphere and stress states, and may inform on the stratigraphy of crustal rocks [2]. However, the number of slip events, linkage, and reactivation may affect the Dmax/L ratios [3]. The investigation of current seismicity on Mars is the motivation for a renewed and detailed analysis of the fault systems of Mars. Using Digital Elevation Models (DEM) and corresponding orthoimages derived from High Resolution Stereo Camera (HRSC) data, we obtained information on the displacement distribution on fault traces as well as the maximum displacement. The Dmax/L ratio is calculated as ~0.007, consistent with previous measurements of martian faults (0.006; [4]). Based on these analyses, we discuss the implications of fault segmentation and linkage for further interpretation. Introduction Detailed investigation on geometric fault properties can provide insights into the mechanical and temporal evolution of fault systems [5,6], and the past and future potential for seismic energy release [7]. In planetary science, where a lack of seismometers is unfortunately the rule rather than the exception, the analysis of faults with remote sensing data typically provides the only direct observational evidence to constrain the tectonic history of a planet [1]. Since the seismic moment released during the growth of a fault is strongly connected to the fault geometry, the study of fault populations can also help to estimate the current seismicity level [2,8]. Until today, only a few data on the relationships between fault displacement and length have been collected for extraterrestrial bodies [9], partly due to the limited number of reliable topographic datasets. The InSight mission put a lander in the Elysium region of Mars in 2018. It is equipped with a seismometer [10] that has recorded several marsquakes for which the locations could be determined [11]. As a starting point for our analysis of fault geometries, we selected the Memnonia Fossae fracture system, one of the closest fracture sets to the InSight landing site, which radiates outward from the Tharsis region in a southwesterly direction. Data and Methods All topographic measurements in this study are based on Digital Elevation Models (DEM) based on HRSC data (High Resolution Stereo Camera; [10]). As HRSC is a push-broom scanning instrument with nine CCD line detectors mounted in parallel on a focal plane, its unique feature is the ability to obtain imaging data at high resolution, with along-track triple stereo, four colors and five different phase angles. The spatial scale of HRSC is 10 m/pixel at the nominal periapsis altitude of 250 km, with an image swath of 53 km. Figure 1: Images show faults from Memnonia Fossae region with three different image system: a. Orthoimage from HRSC, b. DEM derived from HRSC data, c. CTX image. We use DEM and orthoimages from HRSC [10] to obtain information on the displacement distribution along fault traces. This also enabled determining the maximum displacement. We compare our results to previous measurements of faults on Mars, Earth, and beyond. Based on these analyses, we discuss the implications of fault segmentation and linkage for further interpretation. HRSC data offer high-resolution topography and spatially contiguous coverage, which are required to analyze detailed topographic characteristics of large fault systems. For structural interpretation of key locations (e.g., relay ramps), CTX images (~5-6 m px-1) have been inspected. Fault length was digitized along the fault line, and multiple topographic cross-sections across the fault were drawn with a spacing of ~1 km. Fault throw (a proxy for true displacement) was visually determined in the digitized cross-sections.ResultsAt the time of writing, 16 images out of 75 available images/DEM from the Memnonia Fossae region exhibiting normal faults have been investigated. In this preliminary stage, a total number of 83 faults in Memnonia Fossae were studied. We find an average Dmax/L ratio of 0.007, consistent with our previous findings for other regions on Mars, where this ratio had an average value of 0.006 [4].References[1] Schultz, R.A. et al. (2010) J. Struct. Geol., 32, 855-875. [2] Golombek, M.P. et al. (1992) Science 258, 979-981. [3] ] Kim, Y., Sanderson, D. J. (2005) Earth Sci. Reviews, 68, 317-334. [4] Hauber, E. et al. (2014) Lunar Planet. Sci. Conf. 45, #1981. [5] Cartwright, J. A., et al., J. Struct. Geol. 17, 1319-1326, 1995. [6] Cowie, P.A. and Scholz, C.H., J. Struct. Geol. 14, 1133-1148, 1992. [7] Wells, D.L. and Coppersmith, K.J. (1994) Bull. Seismol. Soc. Amer., 84, 974-1002. [8] Knapmeyer, M. et al. (2006) J. Geophys. Res., 111, E11006. [9] Schultz, R.A. et al. (2006) J. Struct. Geol., 28, 2182-2193. [10] Lognonné, P., et al., (2019) Space Science Reviews, 215(1), 1-70. [11] Drilleau, M., et al., (2021) EGU General Assembly. Conf. 14998. [12] Gwinner et al., Planetary and Space Science 126 (2016) 93-138