Sandstone outcrops seen with the ExoMars PanCam emulator

Post by Dr. Peter Fawdon, (@DrPfawdon) School of Physical Sciences, The Open University, United Kingdom

PanCam (Coates et al., 2017) is the imaging instrument on the 2020 ExoMars rover and consists of two wide angle cameras; (WAC’s) and a High Resolution Camera (HRC). PanCam will be used to lead the geological characterisation of the local area outcrops. It will be used to establishing the geological setting of outcrops and identify targets for subsurface sampling and analysis with the ExoMars drill and suite of analytical instruments (Vago et al., 2017).

An emulator for the ExoMars PanCam instrument has been used in rover operation field trials in southern Spain. The aim of these trials has been to explore how scientists will use the instruments in rover missions. These images, taken by the emulator, are examples of what PanCam data might look like and show how the PanCam images will be used (e.g., Harris et al., 2015).

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Image 1: PanCam Multi-spectral images: (A) A colour composite made from the red, green and blue filters shows a ridge named ‘Glengoyne’ at approximately 20 m distance from the rover. (B) A Multi spectral image using the geology filters stretched to emphasise the variation in the scene.

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Universality of delta bifurcations

Post by Dr. Robert C. Mahon, Department of Earth and Environmental Science, University of New Orleans

Which morphologic features of sedimentary systems persist into the stratigraphic record? Ancient river deltas preserved as stratigraphic deposits on both Earth and Mars exhibit remarkable morphologic similarities to modern deltas on Earth (Images 1-3). While channel dynamics may be expected to alter the geomorphic expressions of past channel networks, in many cases channel bodies appear to be preserved in their original configurations. Fully understanding the ways in which geomorphic features become preserved as stratigraphy can provide tools for us to both infer past processes from the ancient deposits with greater confidence, as well as to predict the geometries of ancient deposits in the subsurface (i.e. for resource exploration).

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Image 1: CTX image mosaic of a delta in the Aeolis region of Mars, showing distributary channel networks. CTX imagery courtesy of NASA-MRO/JPL/UA.

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The Largest Delta on Mars?

Post by Jacob Adler, School of Earth and Space Exploration, Arizona State University.

Ancient river deltas are found in many locations on Mars [see Di Achile & Hynek, 2010 and references therein], and are formed as sediment drops out of suspension in water as it approaches a wider shoreline of a lake, sea, or (debatably) an ocean. Some proposed deltas on Mars are found in closed basins (e.g. an impact crater) away from the Martian dichotomy boundary, implying an ancient climate during which the crater ponded with water [e.g. Eberswalde or Jezero]. Occasionally, inlet and outlet river valleys are seen at different elevations along the crater rim, lending further evidence to the hypothesis that the crater filled with liquid water at least up to the outlet elevation. Deltas found in open basins, on the other hand, imply a larger body of standing water, and Mars scientists look for other clues to support the deltaic rather than alluvial fan formation mechanism. In our recent papers, we tested whether the Hypanis fan-shaped deposit (Image 1) could be a delta, and discussed whether this supports the hypothesis that there was once a large sea or ocean in the Northern plains of Mars [Adler et al., 2018; Fawdon et al., 2018].

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Image 1: a) The Hypanis deposit stands out as light-toned in the center of this Mars Reconnaissance Orbiter (MRO) Context Camera (CTX) mosaic of our study region. Also marked are Lederberg crater, and the Sabrina deposit in the closed basin of Magong crater. (b) Hypanis and Sabrina have a low nighttime temperature (dark) as recorded by the THEMIS instrument on Mars Odyssey, suggesting it is mostly composed of small grain size material. Image from the Nighttime IR 100m Global Mosaic v14.0 [Hill et al. (2014); Edwards (2011)] and from the Northern Hypanis Valles Night IR Mosaic [Fergason (2009)]. NASA/JPL/ASU. (c) Our proposed fluvial sequence discussed in the paper. Main lobe (A) could once have had continuous layered beds spanning to the distal island deposits (E). The cross-cutting relationships we observed are consistent with hypothesized shoreline regression to the north. Flow migrated to the northern lobe (B), then to braided inverted channels (C and D) as water retreated. NASA/MSSS/USGS. d) Our digital elevation mosaic shows the topography of Hypanis and surrounding features. Elevations are colored from white (-2500 m) to light green (-2800 m).

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Measuring Cross-Bed Geometry in Upper Aeolis Mons, Gale Crater, Mars

Post by Dr. Ryan B. Anderson, Astrogeology Science Center, United States Geological Survey

One of the most environmentally diagnostic features of sedimentary rocks is cross-bedding, which occurs when sediment is transported by wind, water, or volcanic processes, resulting in horizontal strata composed of inclined beds. The geometry of cross-bedded sedimentary deposits provides information about the depositional setting and post-depositional history of the rocks, making the identification, measurement, and interpretation of cross-beds particularly interesting on Mars, where past conditions are of great scientific interest. This post describes cross-bedding in Upper Aeolis Mons in Gale crater (Image 1).

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Image 1: Example of complex bedding patterns in upper Aeolis Mons, interpreted to be large-scale aeolian cross beds. Image is an inset of HiRISE observation PSP_001620_1750.

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Enigmatic Normal Faults on Ceres

Post by Kynan Hughson, Department of Earth, Planetary, and Space Sciences, University of California, Los Angeles, USA.

Since March of 2015 NASA’s Dawn spacecraft has been actively exploring the main asteroid belt’s largest member and only dwarf planet in the inner solar system: Ceres. Situated around two fifths of the way between the orbits of Mars and Jupiter, Ceres is gargantuan compared to its neighbors. With a mean diameter of ~946 km (approximately the width of the state of Texas) and a bulk density of ~2.16 g/cm3 it comprises around one third of the mass of the entire main belt. Dawn’s continuing examination of this unique object since March 2015 has revealed a geologically diverse world covered with geomorphological features common to both rocky inner solar system planets and icy outer solar system satellites (e.g. Bland et al., 2016; Schmidt et al., 2017; Fu et al., 2017). These observations have exacerbated Ceres’ refusal to be neatly categorized as either a rocky or icy planet.

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Image 1: A rotating aerial view of Nar Sulcus (centered at approximately 79.9 °W, 41.9 °S). Note the two nearly perpendicular sets of fractures. In particular, note the imbricated blocks within the longer fracture set. The longer fracture set is approximately 45 km long, and the deepest valleys are ~400 m deep. This scene was created using a stereophotogrammetrically (SPG) derived elevation model (vertical resolution ~15 m) and high resolution (~35 m/pixel) Dawn framing camera mosaics (Roatsch et al., 2016a; Roatsch et al., 2016b), which are available on the Small Bodies Node of NASA’s Planetary Data System.

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What is happening in Titan’s equatorial belt?

Post by Jeremy BrossierDeutsches Zentrum für Luft- und Raumfahrt (DLR), Institute of Planetary Research, Berlin, Germany.

During the last thirteen years (2004 – 2017), the Cassini-Huygens mission allowed a real revolution in the exploration of Titan, the largest moon of Saturn. This mission has revealed that Titan is – in many aspects – very similar to Earth. Titan is a frozen version of Earth, where methane behaves as water, and water ice may be as hard as rock. Despite its strange characteristics, Titan undergoes a rich variety of surface processes that are likewise analogous to those on our planet. Titan being entirely shrouded by a dense atmosphere made of dinitrogen, methane and solid organic particles (i.e. tholins), direct observation of its surface is only possible through radar data, as well as infrared data within specific wavelengths intervals. SAR images from the radar, allowed identifying various landscapes on the moon (see Image 1), and evaluating their global distribution, notably for the lakes and dunes. Lakes are mostly confined around the poles, while the dunes dominate the equatorial belt. Thus, the shape of Titan’s surface seems quite well understood thank to SAR images, however, it is crucial to determine not only the morphology, but also the nature of the material composing or coating the various landscapes to better understand the geology of this intriguing moon.

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Image 1: A few examples of Titan’s landscapes seen through SAR images, including (A) mountain chains embayed by plains, (B) undifferentiated plains, (C) impact crater, (D) dunes, (E) river channels, (F) small lakes, and (G) a close up of the second largest sea, namely Ligeia Mare. SAR images were acquired during Titan flybys (A, B) T43 in May 2008, (C) T77 in June 2011, (D) T21 in Dec. 2006, (E) T44 in May 2008, (F) T19 in Oct. 2006, and finally (G) T28 in April 2007. Note that Titan flybys are tagged with the abbreviated target name “T” and the flyby number.

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Morphological Evidence that Titan’s Southern Hemisphere Basins are Paleoseas

Post by Samuel Birch, Cornell University, Ithaca, USA.

Titan is the only body in the solar system, besides the Earth, known to currently have standing bodies of liquids on its surface [Stofan et al., 2007]. Presently, liquids are restricted to the polar regions (>50o) with liquid bodies in the North encompassing 35 times more area as compared to the South [Hayes et al., 2011; Birch et al., 2017a]. Apsidal precession of Titan’s obliquity over ~100,000 year cycles, analogous to the Earth’s Croll-Milankovitch cycles, likely forces liquids from pole-to-pole, and has been invoked as a physically plausible mechanism to account for the dichotomy [Aharonson et al., 2009]. General circulation models support such a mechanism, as Titan’s current orbital configuration produces more intense, high-latitude, baroclinic eddies over the southern hemisphere, preferentially depositing more liquid at the northern pole [Lora & Mitchell, 2015]. These models, therefore, imply that the presence of northern liquids is transient over geologic timescales. Large basins able to accommodate ~70,000 km3 of liquid methane and ethane [Hayes, 2016] are required when orbital and climatic conditions become favorable for the accumulation of southern seas. Our study [Birch et al. 2017b] identifies four large basins, all of which show morphological evidence for having been formerly filled by liquids.

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Image 1: Polar stereographic projection of SAR image data of the South polar region extending out to 60o latitude. SAR image data includes all flybys up to and including T98. A mosaic of ISS data underlays the SAR mosaic. The perimeters of the four basins that we identified are highlighted in yellow.

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Stepped Fans and Phyllosilicates on Mars

Post by Peter Grindrod, Natural History Museum, London, UK.

A number of different studies have catalogued features on Mars that could be given the general heading of sedimentary fans [e.g. Irwin et al., 2005; Kraal et al. 2008]. These features occur whenever the velocity of a river or stream decreases, and the water no longer has enough energy to carry its sediment, and thus begins to deposit its load. This drop in energy often occurs when the water flows into flatter and wider regions. The distribution of these fans on Mars is important because it shows the location of past water flows, and the amount of material that has been transported (which can be used as a proxy for flow duration).

However, one of the fundamental problems when looking at these features with orbital data alone, is that it is difficult to determine whether the river flowed into a standing body of water (for example a lake) or just an empty canyon or crater. Of course, the implications of this problem are important if we want to understand the volume and distribution of past water on Mars, which in themselves feed into understanding the past climate and even habitability of Mars.

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Image 1: Location of the two fans in Coprates Catena, SE Valles Marineris. MOLA elevation overlain on THEMIS daytime image.

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Geologically recent glacial melting on Mars

Post by Frances. E. G. Butcher, School of Physical Sciences, Open University, UK.

Thousands of putative debris-covered glaciers in Mars’ middle latitudes host water ice in volumes comparable to that of all glaciers and ice caps on Earth, excluding the Greenland and Antarctic ice sheets (Levy et al., 2014). These glaciers formed within the last 100 million to 1 billion years of Mars’ geological history (Berman et al., 2015), a period that is thought to have been similarly cold and hyper-arid to present-day Mars. This is broadly corroborated by a sparsity of evidence for melting of these geologically ‘young’ mid-latitude glaciers, which suggests that they have always been entirely frozen to their beds in ‘cold-based’ thermal regimes, and haven’t generated meltwater (e.g. Marchant and Head, 2007). Nevertheless, this months’ planetary geomorphology image provides evidence for melting of one such glacier.

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Image 1: An esker emerging from the tongue of a debris-covered glacier in Tempe Terra, Mars. See Image 2 for an annotated 3D view of this scene. The dashed white line delineates the terminus of the debris-covered glacier, which occupies the southern and eastern portions of the image. The white arrow marked A indicates the first emergence of the crest of the esker ridge from the glacier surface. The white arrow marked A’ indicates the northernmost end of the esker ridge in the deglaciated zone beyond the ice terminus. Context Camera image P05_002907_2258_XN_45N083W (Malin et al., 2007). Modified from Butcher et al., 2017 under a Creative Commons license CC BY 4.0.

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Enigmatic Clastic Polygons on Mars

Post by Laura Brooker, Open University, Milton Keynes, UK.

Polygonal ground of centimetre- to decametre-scale is one of the most common features found in cold-climate regions on Earth and on Mars. Polygonal shapes on Earth can form through a number of different processes including the thermal contraction of ice-cemented soils, forming fracture patterns known as thermal contraction polygons, through the freezing and thawing of ground ice moving clasts, in the case of sorted patterned ground, or through the dehydration of volatile-rich material, termed desiccation polygons. Around a large crater found in the northern latitudes of Mars, named Lyot, we observe stunning and unusually large clastic polygons (Image 1), but how do they form? To understand landforms on Mars we turn to analogues on Earth and compare morphological data to look for similarities and differences.

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Image 1: HiRISE (ESP_016985_2315) image of clastic polygonal ground observed to the north east of Lyot crater, Mars. These enigmatic polygons are demarcated by clastic material in their borders and are averagely 130 metres in diameter. Image credit: NASA/JPL/University of Arizona.

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