Gerhard Neukum

Freie Universität Berlin, Berlín, Berlin, Germany

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Publications (325)411.96 Total impact

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    ABSTRACT: Tethys, 1072 km in diameter, is a mid-sized icy moon of Saturn imaged for the first time in two Voyager flybys [1][2][3]. Since July 2004, its surface has been imaged by the Cassini ISS cameras at resolutions between 200 and 500 m/pxl. We present results from our ongoing work to define and map geologic units in camera images obtained preferentially during Cassini’s Equinox and Solstice mission phases. In the majority of Tethys’ surface area a densely cratered plains unit [1][2][3][this work] is abundant. The prominent graben system of Ithaca Chasma is mapped as fractured cratered plains. Impact crater and basin materials can be subdivided into three degradational classes. Odysseus is a fresh large impact basin younger than Ithaca Chasma according to crater counts [4]. Heavily degraded craters and basins occur in the densely cratered plains unit. A smooth, less densely cratered plains unit in the trailing hemisphere was previously identified by [2] but mapping of its boundaries is difficult due to varying viewing geometries of ISS images. To the south of Odysseus, we identified a cratered plains unit not seen in Voyager data, characterized by remnants of highly degraded large craters superimposed by younger fresher craters with a lower crater density compared to the densely cratered plains unit. Its distinct linear northern contact with the densely cratered plains suggests a tectonic origin. Sets of minor fractures can be distinguished in the densely cratered plains, and locally, features of mass wasting can be observed. References: [1] Smith B. A. et al. (1981), Science 212, 163-191. [2] Smith B. A. et al. (1982), Science 215, 504-537. [3] Moore J. M. and Ahern J. L. (1983), JGR 88 (suppl.), A577-A584. [4] Giese B. et al. (2007), GRL 34, doi:10.1029/2007GL031467.
    45th DPS Meeting; 10/2013
  • Lorenz Wendt, Janice L. Bishop, Gerhard Neukum
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    ABSTRACT: We investigate the stratigraphy, morphology and mineralogy of five major knob fields in the region between Terra Cimmeria and Terra Sirenum on Mars based on HRSC, CTX, MOC and HiRISE imagery together with hyperspectral data from CRISM. The knob fields comprise Ariadnes Colles, Atlantis Chaos and Gorgonum Chaos and further, unnamed fields of mounds. They have been mapped in previous studies as Hesperian or Amazonian units and are located within the shoreline of the proposed “Eridania lake”, the putative source of Ma’adim Vallis. The mounds contain Mg/Fe-bearing phyllosilicates and locally Al-rich phyllosilicates. Our geological mapping shows that the knob fields have a late Noachian age, which indicates later phyllosilicate formation than typically observed on Mars. The knob fields formed by alteration of the “Electris deposit”, an airfall deposit possibly rich in basaltic glass (Grant, J.A., Schultz, P.H. [1990]. Icarus 84, 166–195), in local depressions, possibly in the Eridania lake. The spectroscopic detection of phyllosilicates here may indicate that liquid water persisted longer in this region than elsewhere on Mars. The knob fields are embayed by the Hesperian ridged plains. Numerous valleys carve into the ridged plains and document that the aqueous history of this region continued into the Hesperian and Amazonian. The study area is traversed by the Sirenum Fossae. These graben appear to post-date the aqueous activity in the study area except in the Gorgonum basin, where a lake developed after their formation.
    Icarus 07/2013; 225(1):200–215. · 3.16 Impact Factor
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    ABSTRACT: The determination of the gravity field of Phobos up to second-order terms is the main objective of future close flybys of the Martian moon by Mars Express (MEX). Such flybys at close distance (typically less than 60 km from the center) are needed to obtain the signature of the second-degree coefficients of the gravity field of the moon in the spacecraft orbit. However, a major issue is that a precise knowledge of the position of Phobos at the time of each flyby is critical in order to avoid significant biases on the retrieval of the gravity field coefficients from the reconstruction of the MEX orbit. In order to overcome this problem, we have proposed in the frame of the European FP7 ESPaCE network the idea to perform a series of astrometric measurements of Phobos around the Mars Express flyby(s), with the Super-Resolution-Channel (SRC) of the HRSC camera onboard MEX. Based on these measurements, an improved ephemeris of Phobos' orbit specifically designed around the flyby is generated. Then, it can be used in a global inversion scheme with radio-tracking data of the spacecraft acquired during and around the flyby, in order to obtain a very precise and accurate solution of the gravity field of Phobos. In this study, we present this innovative methodology that may be used for future Mars Express flybys. Numerical simulations are run to quantify the error on the determination of the gravity field as a function of the uncertainty on its orbit. A strategy to optimize the use of the SRC operation is also developed.
    04/2013;
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    ABSTRACT: Tethys, with a diameter of 1060 km one of the 6 mid-sized icy moons of Saturn, was imaged for the first time in the early 1980ies by the cameras aboard the two Voyager spacecraft at resolutions of 1 km/pxl and lower [1][2][3]. These images show that most of Tethys is densely cratered and displays two major landmarks: the ~ 400 km large impact structure Odysseus and the huge graben system of Ithaca Chasma [1][2]. Since July 2004, Cassini has been in orbit about Saturn and has made several close passes at Tethys, providing an almost complete global image coverage at regional scale (200 - 500 m/pxl). However, varying viewing geometries between images taken during different orbits still impede the identification and mapping of geologic units. In this work we present an update of Tethys' regional geology and stratigraphy, based on Cassini ISS images. Crater distribution measurements, by us and in comparison with measurements of other groups [4], are used to support stratigraphic findings. Most of Tethys' surface consists of a hilly, rugged, heavily cratered plains unit, as identified in Voyager images [1][2][3]. A smooth, less densely cratered plains unit in the trailing hemisphere was previously observed by [2] which is also identifiable in Cassini ISS, but its exact boundaries are difficult to map due to varying viewing geometries of ISS observations. Another sparsely cratered plains unit not seen in Voyager images can be located to the south of Odysseus. It features remnants of highly degraded large craters superimposed by younger fresher craters with a lower crater density compared to the heavily cratered plains. Its distinct linear northern contact with the heavily cratered plains suggests an origin related to tectonism. Again, varying viewing conditions hamper to map the exact boundaries of this unit. The prominent graben system of Ithaca Chasma represents fractured cratered plains. The high resolution of Cassini ISS images reveals that tectonism on Tethys is more widespread. Numerous fractures can be identified locally in the heavily cratered plains. Impact crater materials can be subdivided into three degradational classes. Oldest crater forms are heavily degraded impact structures, such as Telemus. Odysseus is a fresh to partly degraded large impact structure with a central peak complex, wall terraces, secondary crater chains, and slivers of smooth deposits within the heavily cratered plains, possibly impact ejecta. According to previous ISS-based crater measurements, Odysseus is younger than Ithaca Chasma and possibly did not cause the formation of this graben system [5]. The youngest and freshest craters are represented by Telemachus, characterized by a sharp crater rim, well-discernible ejecta blankets, and a low superimposed crater frequency. Locally, features of mass wasting, e.g. landslides, can be observed in craters. References: [1] Smith B. A. et al. (1981), Science 212, 163-191. [2] Smith B. A. et al. (1982), Science 215, 504-537. [3] Moore J. M. and Ahern J. L. (1983), JGR 88 (suppl.), A577-A584. [4] Kirchoff M. R. and Schenk P. M. (2010), Icarus 206, 485-497. [5] Giese B. et al. (2007), GRL 34, doi:10.1029/2007GL031467.
    04/2013;
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    ABSTRACT: In July 2012 the Dawn spacecraft completed its mapping task of the Main Belt asteroid Vesta with a second high altitude mapping orbit. Dawn is now on its way to the dwarf planet (1) Ceres, where it will perform a similar mapping campaign like that at Vesta [1]. The Main Belt is the source region of most impactors in the inner solar system [2,3,4], making it a key region for understanding the early history of our Solar System. In order to determine absolute surface ages from Vesta we derived a crater production function and a chronology function for Vesta. We derived these functions from the respective lunar functions [2] and scaled [5] them to the impact conditions on Vesta [6]. In general we find good agreement between the derived crater production function and the measured crater distribution. However, we also find disagreement between 8 and 15 km crater size, on areas older ~2.2 Ga. Older areas show a steep (~-6 cumulative) slope, which we link to a decaying influence of the vestan collisional family (Vestoids). The lower boundary of 8 km crater size may be explained by fast ejected small spalls and/or a more efficient Yarkovsky effect [7]. This influence is not observed for instance inside the large Rheasilvia basin, which we date with ~2.2 Ga. Since the formation of this basin is believed to be a major source of replenishment of the Vestoids, it's currently observed cratering record is not indicative for the basin formation age in contrast to [8]. The young interior of the Rheasilvia basin is likely a result of repeated resets of the crater retention age due to mass wasting processes on the basin walls. We use topographic heights, which are less affected by mass wasting such as the top of the central peak of the basin as well as proximal ejecta blankets outside the basin to date the formation age of Rheasilvia. For the central peak we derive a surface age of 3.59 (+0.079/-0.18) Ga. The proximal ejecta blanket at the Oppia crater is dated with 3.62 (+0.054/-0.087) Ga and 3.63 (+0.058/-0.096) Ga. We also find seismic (miniscule ejecta blanket from Rheasilvia) resurfacing events in the time frame of ~3.56 to ~3.59 Ga at several areas in the northern hemisphere, indicative for a major seismic activity probably connected to the Rheasilvia formation. An antipodal activity is also suggested by hydrocode modeling [9]. By summation of age probability curves of measurements we link to the Rheasilvia formation, we find 3.58 (+0.07/-0.12) Ga. Using a similar attempt we find 3.75 (+0.05/-0.21) Ga for the Veneneia formation. Both crater retention ages correspond within the error bars with prominent peaks of independent Ar-Ar ages of Vesta related HED meteorites [10]. Acknowledgement: This work has been supported by the German Space Agency (DLR) on behalf of the Federal Ministry of Economics and Technology, grants 50OW1101(NS,TK), 50QM1001 (GM) and 50OW1102 (OR,HH). References: [1] Russell et al. (2007): Advances in Space Research 40(2): pp193-201, 2007. [2] Neukum and Ivanov: In: Gehrels T (ed) "Hazards due to comets and asteroids". University of Arizona Press, Tucson, 359-416, 1994. [3] O'Brien and Greenberg (2005): Icarus 178(1): 179-212. [4] Nesvorny et al. (2009): Icarus 200(2): 698-701. [5] Ivanov (2001): Chronology and Evolution of Mars 96, 87-104, 2001. [6] Schmedemann et al. (2012): 43.LPSC, The Woodlands, #1659. [7] Morbidelli et al. (2003): Icarus 162, 328-336. [8] Marchi et al. (2012): Science 336, 690. [9] Bowling et al. (2012): 75th Annual Meeting of the Meteoritical Society, 2012, Cairns, Australia. Meteoritics and Planetary Science Supplement, id.5256. [10] Bogard, D. D. (2011): Chemie der Erde - Geochemistry, vol. 71, issue 3: 207-226.
    04/2013; 71(3: 207-226. Bibtex entry for this abstract <a href="http://adsabs.harvard.edu/cgi-bin/nph-abs_connect?bibcode=2013EGUGA..15.5741S&data_type=Custom&format=%5c%5cbibitem%5b%25%5c2m%25%28y%29%5d%25%7bR%7d%20%25%5c5.3l%20%25%5cY):5741-.
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    ABSTRACT: The Cassini Imaging Science Subsystem (ISS )acquired 370 high-resolution images (500 m/pixel) of Rhea during two close flybys and 9 non-targeted flybys between 2004 and 2010. We combined these images with lower-resolution Cassini images and others taken by the Voyager cameras to produce a high-resolution semi-controlled mosaic of Rhea. This global mosaic is the baseline for a high-resolution Rhea atlas. The nomenclature used in this atlas was proposed by the Cassin iimaging team and approved by the International Astronomical Union (IAU). The atlas is available to the public through the Imaging Team’s website /http://ciclops.org/maps and the Planetary Data System /http://pds.jpl.nasa.gov. This atlas completes the series of the atlases of the Saturnian medium-sized satellites Mimas, Enceladus, Tethys, Dione, Rhea, and Iapetus.
    Planetary and Space Science 02/2012; 61(2012):135-141. · 2.11 Impact Factor
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    ABSTRACT: Approach imaging of Vesta by the Dawn spacecraft (Russell et al., 2007) show that the south polar topographic anomaly first observed by HST (Thomas et al., 1997), is a complex and unique geologic structure. A dense set of concentric arcuate, cuspate, and spiral inward-facing scarps and ridges form a coherent ~460-525 km wide annular feature. This region is bounded by a set of asymmetric and discontinuous inward-facing scarps several kilometers high. The center is dominated by a large central mountain ~200 km wide and 10-15 km high. The topography is complex, broadly circular with a large circular extension to one side. Three models for the origin of this structure have been proposed. Key tests of the HST-based large impact model include impact melt and ejecta but approach imagery is not yet of sufficient resolution to unambiguously detect these. Nevertheless, comparison to large impact features on Hyperion, Rhea and Iapetus suggest a basic similarity in planform to the large central mound and arcuate inward-facing scarps on Vesta. Alternatively, the complex interior can be interpreted as the manifestation of a large downwelling mantle plume. Broadly similar structures have been observed on Miranda and Enceladus, although these lack large central mounds. The third model suggests extensive post-impact deformation of a large impact feature. Rapid rotation during impact (Jutzi and Asphaug, 2011) may also explain some of the anomalous features. Impact ejecta and global fracturing may have profoundly altered Vestan geology. Large equatorial troughs may be related to the formation process or post-impact deformation. The confirmation of any of these models and their effects will required the detailed imagery, topography, compositional (VIR and GRaND), geologic and gravity mapping observations planned by Dawn. Preliminary crater counts indicate a possible surface model age of ~3.8 Gyr for the south polar structure. However, the structure is morphologically well preserved and not deeply eroded, suggesting that planned mapping will yield many surprises. The authors acknowledge the support of the Dawn Science, Instrument and Operations Teams.
    AGU Fall Meeting 2011; 12/2011
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    ABSTRACT: 4 Vesta is a miniature (proto) planet. Its nearly spherical shape indicates that it was formed in hydrostatic equilibrium. Vesta is considered the parent body of the HED meteorites, achondrites that experienced extensive igneous processing, and therefore it is expected that Vesta is a differentiated body, probably the smallest of our solar system. The images by the Framing Camera onboard Dawn display a surface with complex topography due to impacts and possibly endogenic processes. Features and processes on the lunar surface are often used for comparison in order to understand the geomorphology and geophysics of Vesta. Vesta's diameter, however, is 6.5 times smaller than that of the Moon. It is comparable to those of other big asteroids and about 5 times the mean diameter of the asteroid 21 Lutetia. Lutetia was recently observed by the Rosetta spacecraft during a flyby. Its mass and volume were determined to yield a density of 3400 kg/m3. The densities of the Moon, Vesta, and Lutetia are similar within the error bars and hence surface gravity and escape velocity scale with the radii of these bodies. These parameters (density, surface gravity, and escape velocity) strongly influence crater forming dynamics. Geomorphologic features on Vesta and Lutetia can be directly compared because the scales of images taken during the Dawn high altitude mapping orbit (HAMO) and those of Rosetta are both about 60 m/pixel. The number densities and properties of impactors should have been rather similar for both asteroids considering their mean heliocentric distances. A direct comparison with Lutetia's properties (shape, geomorphology, crater size distribution, and variegation) will help to constrain parameters of processes on Vesta and possibly be useful to separate exogenic from endogenic effects.
    AGU Fall Meeting 2011; 12/2011
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    ABSTRACT: Images of the asteroid and protoplanet 4Vesta by the Hubble Space Telescope in 1994 and 1996 revealed a ~460 km diameter feature at its south pole that was interpreted to be a large impact structure. NASA's Dawn spacecraft arrived at the asteroid Vesta on July 15, 2011 and collected science data during the approach to Vesta, a circular polar orbit at an altitude of 2700 km providing ~ 230 m/pix camera resolution and a lower main mapping orbit, at 700 km altitude with a camera resolution of ~ 65 m/pixel. As part of the geological analysis of Vesta's surface, a series of 15 quadrangle maps are being produced. We present the results of the geological mapping achieved for quadrangle V-15SP. Unit boundaries and feature characteristics were determined primarily using morphologic data. Color and spectral data was utilized to refine unit contacts and to separate compositional or mineralogical distinctions. Those units that could be discerned both in morphology and in the color data were interpreted as geologically derived units. The south polar feature is a semi-circular structure with a central hill that is characterized by a white-grey color and smoother texture distinctive from the surrounding terrain. Some images show patches of bright, smooth terrain on the central hill, perhaps indicative of impact melt or ponded volcanic flows. A complex network of deep grooves and ridges is the primary characteristic on the feature floor; these grooves appear radial to the central mound or trend along a north-south line. The structure also has a distinctive color from both the central hill and surrounding terrain, consistent with a different composition or texture. A steep semi-arcuate scarp bounds part of the outer perimeter of the south polar feature. Although asymmetric in general form, these characteristics do not contradict an impact origin but may also allow endogenic processes like convective downwelling or hybrid modification of an impact. Rapid rotation of Vesta during impact may explain some anomalous features (Jutzi and Asphaug, 2010). The crater size frequency and the chronology function is derived from the lunar chronology, scaled to impact frequencies modeled for Vesta according to (Bottke et al., 1994) and (O'Brien and Sykes, 2011) on Vesta. Preliminary crater counts indicate only small differences in absolute surface model ages between the northern region and the south polar structure.
    AGu fall Meeting 2011; 12/2011
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    ABSTRACT: Observations from the Dawn (Russell et al., 2007) spacecraft enabled deriva-tion of 4Vesta's shape, facilitated mapping of the surface geology and pro-vided the first evidence for Vesta's geological evolution. The Dawn mission is equipped with a framing camera (FC), a visible and infrared mapping spectrometer (VIR) and a gamma-ray and neutron detector (GRaND). So far science data are collected during the approach to the asteroid and protoplanet Vesta, a circular polar orbit at an altitude of 2700 km providing ~ 230 m/pix camera resolution and a lower orbit, at 700 km altitude with a camera resolu-tion of ~ 65 m/pixel. Geomorphology and distribution of surface features provide evidence for impact cratering, tectonic activity, regolith and prob-able volcanic processes. Craters with dark rays, bright rays, and dark rim streaks have been observed, suggesting possible buried stratigraphy. The largest fresh craters retain a simple bowl-shaped morphology, with depth/diameter ratios roughly comparable to lunar values. The largest candi-date crater, a ~460 km depression at the south pole, has been shown to con-tain an incomplete inward facing cuspate scarp, and a large central mound surrounded by unusual complex arcuate ridge and groove patterns. Although asymmetric in general form, these characteristics do not contradict an impact origin but may also allow endogenic processes like convective downwelling or hybrid modification of an impact. Rapid rotation of Vesta during impact may explain some anomalous features (Jutzi and Asphaug, 2010). A set of large equatorial troughs may be related to the formation process of the south polar structure or due to stress caused by changes of the rotational axis. The crater size frequency and the chronology function is derived from the lunar chronology, scaled to impact frequencies modeled for Vesta according to (Bottke et al., 1994) and (O'Brien and Sykes, 2011). The northern hemi-sphere is heavily cratered by a large variety of ancient degraded and fresh sharp craters. Preliminary crater counts indicate only small differences in absolute surface model ages between the northern region and the south polar structure.
    AGU Fall Meeting 2011; 12/2011
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    ABSTRACT: NASA's Dawn spacecraft arrived at the asteroid 4Vesta on July 15, 2011, and is now collecting imaging, spectroscopic, and elemental abundance data during its one-year orbital mission. As part of the geological analysis of the surface, a series of 15 quadrangle maps are being produced based on Framing Camera images (FC: spatial resolution: ~65 m/pixel) along with Visible & Infrared Spectrometer data (VIR: spatial resolution: ~180 m/pixel) obtained during the High-Altitude Mapping Orbit (HAMO). This poster presentation concentrates on our geologic analysis and mapping of quadrangle V-10EW. This quadrangle, located between ±22 degrees and 288-360 degrees E, is dominated by three adjacent large impact craters, whose bright ejecta partially cover a dark terrain reminiscent of buried lunar basaltic material. We are using FC stereo and VIR spectroscopic data to assess whether the dark terrain consists of ancient basaltic material versus other possibilities (e.g., remains of a carbonaceous meteorite, basaltic ejecta, etc.). This quadrangle also contains an enigmatic positive-relief edifice with a central depression and adjacent field of dark material; possible hypotheses for origin of the edifice include the remains of an ancient volcano, a mountain cover by dark ejecta, heavily cratered landscape, or other possibilities. Acknowledgement: The authors acknowledge the support of the Dawn Science, Instrument and Operations Teams.
    AGU Fall Meeting 2011; 12/2011
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    ABSTRACT: NASA's Dawn spacecraft arrived at the asteroid 4Vesta on July 15, 2011, and is now collecting imaging, spectroscopic, and elemental abundance data during its one-year orbital mission. As part of the geological analysis of the surface, a series of 15 quadrangle maps are being produced based on Framing Camera images (FC: spatial resolution: ~65 m/pixel) along with Visible & Infrared Spectrometer data (VIR: spatial resolution: ~180 m/pixel) obtained during the High-Altitude Mapping Orbit (HAMO). This poster presentation concentrates on our geologic analysis and mapping of quadrangle V-12EW. This quadrangle is dominated by the arcuate edge of the large 460+ km diameter south polar topographic feature first observed by HST (Thomas et al., 1997). Sparsely cratered, the portion of this feature covered in V-12EW is characterized by arcuate ridges and troughs forming a generalized arcuate pattern. Mapping of this terrain and the transition to areas to the north will be used to test whether this feature has an impact or other (e.g., internal) origin. We are also using FC stereo and VIR images to assess whether their are any compositional differences between this terrain and areas further to the north, and image data to evaluate the distribution and age of young impact craters within the map area. The authors acknowledge the support of the Dawn Science, Instrument and Operations Teams.
    AGU Fall Meeting 2011; 12/2011
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    ABSTRACT: NASA's Dawn spacecraft arrived at the asteroid 4Vesta on July 15, 2011, and is now collecting imaging, spectroscopic, and elemental abundance data during its one-year orbital mission. As part of the geological analysis of the surface, a series of 15 quadrangle maps are being produced based on Framing Camera images (FC: spatial resolution: ~65 m/pixel) along with Visible & Infrared Spectrometer data (VIR: spatial resolution: ~180 m/pixel) obtained during the High-Altitude Mapping Orbit (HAMO). This poster presentation concentrates on our geologic analysis and mapping of quadrangle V-14SW. This quadrangle can be divided into the northern part which is characterized by a comparatively smooth inter-crater plain and the southern part which is more of a tectonically embossed nature. These tectonic features lie at the northern fringes of the complex network of deep grooves and ridges found in the south-pole area (see V-15SP). In the south-eastern part of this quadrangle we observe an isolated depression possibly associated with a distinct scarp. In general, the material of the southern part of this quadrangle has a higher albedo than the northern part. In a number of cases high-albedo features also seem to be topographically elevated. One of the highest albedo features in the southern hemisphere of Vesta has a spot-like appearance in low resolution image data. It is located in the eastern part of this quadrangle and is associated with several radial high-albedo streaks, similar to ray craters found on other solar system bodies. The western part of this quadrangle shows some small low-albedo areas as well as some craters displaying internal dark and bright radial streaks. We are using FC stereo and VIR spectroscopic data in order to constrain the formation and mineralogy of these bright and dark materials. Acknowledgement: The authors acknowledge the support of the Dawn Science, Instrument and Operations Teams.
    AGU Fall Meeting 2011; 12/2011
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    ABSTRACT: NASA's Dawn spacecraft arrived at the asteroid 4Vesta on July 15, 2011, and is now collecting imaging, spectroscopic, and elemental abundance data during its one-year orbital mission. As part of the geological analysis of Vesta's surface, a series of 15 quadrangle maps are being produced based on the geological mapping results of images obtained by the Framing Camera during the High-Altitude Mapping Orbit (HAMO) (spatial resolution: ~65 m/pixel). In addition compositional information derived from the FC color images as well as from the Visible & Infrared Spectrometer data (spatial resolution: ~180 m/pixel) were taken into account during the mapping process. We present the results of the geological mapping process achieved for the quadrangle V-13SFW. Within the quadrangle boundary are the outer portions of the south polar structure, including a large scarp that likely defines the structure margin and the transition into the equatorial trough unit. Images reveal a heavily cratered surface with impact features of different sizes, morphologies and degree of degradation with morphologically fresh impact craters showing dark or bright rays. Sets of E-W oriented ridges and grooves in the northern part of our region of interest extend up to the equatorial region. In addition a complex network of linear features characterizes the floor of the giant Southern basin. Both types of geological features might be related to the candidate impact event resulting in the Southern basin. Acknowledgement: The authors acknowledge the support of the Dawn Science, Instrument and Operations Teams.
    AGU Fall Meeting 2011; 12/2011
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    ABSTRACT: Our first version of the high-resolution Dione atlas was released in 2008 [1]. Since then, the Cassini Imaging Science Subsystem (ISS) acquired additional high-resolution images (< 800 m/pixel) during ten non-targeted flybys of Dione in 2008, 2009, and 2010. We combined these images with the earlier coverage taken between 2004 and 2007 to improve our global mosaic of Dione (Fig. 1). This new global mosaic is the baseline for our second release of the high-resolution Dione atlas that consists of 15 tiles, each sheet with a scale of 1:1,000,000 (Fig. 2). The nomenclature used in this atlas was proposed by the Cassini imaging team and was approved by the International Astronomical Union (IAU). The new release of the atlas is available to the public through CICLOPS (http://ciclops.org) and PDS (http://pds.jpl.nasa.gov). References [1] Roatsch, Th. et al., High-resolution Atlas of Dione derived from Cassini-ISS images. Planetary Space Sciences 56, 1499-1505, 2008.
    EPSC-DPS2011; 10/2011
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    ABSTRACT: We investigate the formation of the outflow channels Dao and Niger Valles near the eastern rim of the Hellas impact basin, Mars. Methods used include image and topography analysis, surface age determination, and finite element modeling. Observations show that deep depressions, source regions for Dao and Niger Valles, are located in an area of shallow subsidence to the south and east of the volcano Hadriaca Patera. Cratering model ages allow for fluvial processes triggered by volcanic loading. Based on the observations, we develop a numerical model of volcanic loading on top of a poroelastic plate leading to flexure and fracturing of the lithosphere. Modeling results show that fracturing may occur up to a depth of about 6 km within an area of shallow subsidence, i.e., the moat surrounding the volcano. Depending on initial aquifer pressurization, groundwater could have reached the surface. Model discharges and channel morphometry suggest that the Dao Vallis channel never reached bankfull flow and that the wetted channel perimeter may have formed during multiple outflow events. The following scenario is proposed: (1) emplacement of a volcanic load on top of a confined, overpressurized aquifer in the early Hesperian, (2) fracturing around the load, possibly reactivated during various stages of volcanic activity, (3) channeling of groundwater to the surface along fractures and outflow channel formation during several events in the Hesperian, and (4) collapse, mass wasting and modification of depressions in the Amazonian.
    Journal of Geophysical Research Atmospheres 08/2011; 116(E15):8001. · 3.44 Impact Factor
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    ABSTRACT: Tharsis Tholus, a more than 3.9Ga old composite shield volcano to the east of the major Tharsis Montes, has experienced a complex history of growth and destruction. On the basis of new high resolution images we analysed the morphology as well as the tectonic structures of the Tharsis Tholus volcano in detail. From morphological data, cross-cutting relations of the surface structures, and crater modelling ages we propose a chronostratigraphy for the volcano-tectonic history of Tharsis Tholus.The strongly faulted volcano reveals two large-scale landslide events followed by two subsequent shield re-growth phases between 3.8 and 1.7Ga and two caldera collapses. Tharsis Tholus was also affected by regional extensional tectonics between 1.7Ga and 0.4Ga recorded by sub-parallel sets of NE trending graben structures. The steep and up to 5.4km high landslide scarps on Tharsis Tholus suggest deep faulting of the edifice. In order to confirm this hypothesis we used analogue sand box models in which we demonstrated that gravitational flank movement on top of weak basal substrata may have produced the deformation structures as observed on Tharsis Tholus.
    Earth and Planetary Science Letters 05/2011; 305(3-4):445–455. · 4.72 Impact Factor
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    ABSTRACT: Olympus Mons scarp and aureole lobes are investigated with methods of mapping, terrain model analysis and morphometry. Results suggest a landslide mechanism (Source: http://adsabs.harvard.edu/abs/2011LPI....42.1932M).
    Lunar and Planetary Science Conference; 03/2011
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    ABSTRACT: This abstract suggests that the dark materials about Valles Marineris plateau are local, weathered outcrop remnants of in situ, lithified dark-toned layered rocks that erode to form aeolian deposits (Source: http://adsabs.harvard.edu/abs/2011LPI....42.2423C).
    Lunar and Planetary Science Conference; 03/2011

Publication Stats

2k Citations
411.96 Total Impact Points

Institutions

  • 2003–2013
    • Freie Universität Berlin
      • • Institute of Geological Sciences
      • • Division of Planetary Sciences and Remote Sensing
      • • Department of Earth Sciences
      Berlín, Berlin, Germany
  • 2010
    • Arizona State University
      • School of Earth and Space Exploration
      Tempe, AZ, United States
  • 2008–2010
    • International Space Science Institute
      Berna, Bern, Switzerland
    • Université Paris-Sud 11
      • Institut d'Astrophysique Spatiale
      Orsay, Île-de-France, France
    • Brown University
      • Department of Geological Sciences
      Providence, RI, United States
  • 2005–2009
    • Cornell University
      • Department of Astronomy
      Ithaca, NY, United States
  • 1998–2009
    • German Aerospace Center (DLR)
      • Institute of Planetary Research
      Köln, North Rhine-Westphalia, Germany
  • 2007
    • United States Geological Survey
      Reston, Virginia, United States
  • 2006
    • The Space Science Institute
      Boulder, Colorado, United States