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.


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.



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.


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.


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.

Image 1

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.


A Wunda-full world? Carbon dioxide ice deposits on Umbriel and other moons of Uranus

Post contributed by Dr. Mike Sori, Lunar and Planetary Laboratory, University of Arizona

Uranus and its moons have only ever been visited by one spacecraft, Voyager 2, which flew by the system in 1986.  One of its large moons, Umbriel, was found to have a mysterious bright ring 80-km-wide inside a 131-km-diameter crater named Wunda.  Image 1 shows Umbriel and this annulus-shaped feature.


Image 1 blog post

Image 1: Voyager 2 image 1334U2-001 showing the Uranian moon Umbriel; note the bright ring inside the crater Wunda at top of the image (which is at Umbriel’s equator).


Pit chains on Enceladus

Post contributed by Dr. Emily S. Martin, Research Fellow, Center for Earth and Planetary Studies, National Air & Space Museum, Smithsonian Institution.

Pit chains are linear assemblages of circular to elliptical pits and have been observed across the solar system. Pit chains have been found on Venus, Earth, Mars, Phobos, Eros, Gaspra, Ida, and Vesta. Across the solar system, pit chains may form through a variety of mechanisms including the collapse of lava tubes, karst, venting, extensional fracturing, or dilational faulting. Saturn’s tiny icy moon Enceladus is the first body of the outer solar system on which pit chains have been identified. Enceladus is only 500 km in diameter and is best known for its warm south pole and its watery plume emanating from prominent ridges known as tiger stripes. The source of the plume is likely a global liquid water ocean beneath an icy shell.


Image 1: The morphology of pit chains across the solar system. a. Eros from NEAR. Image no. 135344864. b. Phobos. Image PIA10367. c. Albalonga Catena, Vesta. d. Venus. Right-look Magellan data near 13°S, 112°E. e. Kilauea Volcano, Hawaii centered at 19.3909°N 155.3076°W. Image taken 12/06/2014, acquired from Google Earth on 04/20/2016. f. Ida, modified from image PIA00332. g. Gaspra, modified from Galileo image PIA00332. h. Pit chains in north-eastern Iceland centered near 65.9902°N and 16.5301°W. Image taken on 7/27/2012, acquired from Google Earth 04/20/2016. i. Pit chains on Mars from the Mars Global Surveyor Mars Orbiter Camera, centered near 6.5398°S and 119.9703°W on the flank of Arsia Mons. Image PIA02874.


Frozen Seas on Mars and Earth

Posted by
Dr. Matt Balme, Open University, UK. 

(Re-posted from IAG Image of the Month, October, 2007)

Elysium Planitia

Images of the ‘frozen sea’ on Mars (a,b) from the High Resolution Stereo Camera of the ESA Mars Express Mission, and pack-ice (c) in the terrestrial Antarctic.


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