Katharina A. Otto^1,*, Ralf Jaumann^1,2, Katrin Krohn¹, Klaus-Dieter Matz¹, Frank Preusker¹, Thomas Roatsch¹, Paul Schenk³, Frank Scholten¹, Katrin Stephan¹, Carol A. Raymond⁴ and Christopher T. Russell⁵

¹German Aerospace Center, Berlin, Germany
²Institute of Geosciences, Freie Universität Berlin, Berlin, Germany
³Lunar and Planetary Science Institute, Houston, Texas, USA
⁴California Institute of Technology, Jet Propulsion Laboratory, Pasadena, California, USA
⁵Institute of Geophysics and Planetary Physics, University of California, Los Angeles, California, USA

The Rheasilvia crater is Vesta’s largest impact basin. It is a 500 km diameter complex crater centered near the south pole and overlying the 400 km diameter impact basin Veneneia. Using Framing Camera (FC) data from the Dawn spacecraft’s Low Altitude Mapping Orbit (20 m/pixel) and a digital terrain model derived from High Altitude Mapping Orbit stereo data, we identified various mass-wasting features within the south polar region. These features include intra-crater mass movements, flow-like and creep-like structures, slumping areas, landslides, and curved radial and concentric ridges. Intra-crater mass-wasting features are represented by lobate slides, talus material, dark patches on the crater wall, spurs along the crater rim and boulders. Slumping areas develop in compact material, whereas landslides form in relatively loose material. Both may be triggered by seismic shaking induced by impacts. Intra-crater mass wasting and slid and slumped materials are homogeneously distributed throughout the basin. Slumping and sliding processes have contributed most efficiently to basin degradation. Flow-like and creep-like features originate from granular material and cluster between 0°E and 90°E, an area exposing shocked and fractured material from the Rheasilvia impact event. The radial curved ridges are likely to be remnants of the early Rheasilvia collapse process, when radially moving masses were deflected by the Coriolis Effect. The concentric ridges are artifacts from the crater rim collapse. Curved ridges at the intersection of Rheasilvia and Veneneia, and on Rheasilvia’s central peak, may also have been influenced by the Rheasilvia basin relaxation process, and an oblique impact, respectively.

Reference
Otto KA, Jaumann R, Krohn K, Matz K-D, Preusker F, Roatsch T, Schenk P, Scholten F, Stephan K, Raymond CA, and Russell CT (in press) Mass-wasting features and processes in Vesta’s south polar basin Rheasilvia. Journal of Geophysical Research – Planets .
[doi:10.1002/2013JE004333]
Published by arrangement with John Wiley & Sons

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Ivo R. Seitenzahl^1,2,*, Gabriele Cescutti³, Friedrich K. Röpke¹, Ashley J. Ruiter² and Rüdiger Pakmor⁴

¹Institut für Theoretische Physik und Astrophysik, Universität Würzburg, Campus Hubland Nord, Emil-Fischer-Str. 31, 97074 Würzburg, Germany
²Max-Planck-Institut für Astrophysik, Karl-Schwarzschild-Str. 1, 85741 Garching, Germany
³Leibniz-Institut für Astrophysik Potsdam (AIP), An der Sternwarte 16, 14482 Potsdam, Germany
⁴Heidelberger Institut für Theoretische Studien, Schloss-Wolfsbrunnenweg 35, 69118 Heidelberg, Germany

Context. Manganese is predominantly synthesised in Type Ia supernova (SN Ia) explosions. Owing to the entropy dependence of the Mn yield in explosive thermonuclear burning, SNe Ia involving near Chandrasekhar-mass (M_Ch) white dwarfs (WDs) are predicted to produce Mn-to-Fe ratios that significantly exceed those of SN Ia explosions involving sub-Chandrasekhar mass primary WDs. Of all current supernova explosion models, only SN Ia models involving near-M_Ch WDs produce [Mn/Fe] ≳ 0.0.
Aims. Using the specific yields for competing SN Ia scenarios, we aim to constrain the relative fractions of exploding near-M_Ch to sub-M_Ch primary WDs in the Galaxy.
Methods. We extract the Mn yields from three-dimensional thermonuclear supernova simulations that refer to different initial setups and progenitor channels. We then compute the chemical evolution of Mn in the solar neighborhood, assuming SNe Ia are made up of different relative fractions of the considered explosion models.
Results. We find that due to the entropy dependence of freeze-out yields from nuclear statistical equilibrium, [Mn/Fe] depends strongly on the mass of the exploding WD, with near-M_Ch WDs producing substantially higher [Mn/Fe] than sub-M_Ch WDs. Of all nucleosynthetic sources potentially influencing the chemical evolution of Mn, only explosion models involving the thermonuclear incineration of near-M_Ch WDs predict solar or super-solar [Mn/Fe]. Consequently, we find in our chemical evolution calculations that the observed [Mn/Fe] in the solar neighborhood at [Fe/H] ≳ 0.0 cannot be reproduced without near-M_Ch SN Ia primaries. Assuming that 50% of all SNe Ia stem from explosive thermonuclear burning in near-M_Ch WDs results in a good match to data.

Reference
Seitenzahl IR, Cescutti G, Röpke FK, Ruiter AJ and Pakmor R (2013) Solar abundance of manganese: a case for near Chandrasekhar-mass Type Ia supernova progenitors. Astronomy & Astrophysics 559:L5.
[doi:10.1051/0004-6361/201322599]
Reproduced with permission © ESO

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