Harold Clenet^a, Martin Jutzi^b, Jean-Alix Barrat^c, Erik I. Asphaug^c, Willy Benz^b and Philippe Gillet^a

^aEPSL, Institute of Condensed Matter Physics, Ecole Polytechnique Fédérale de Lausanne (EPFL), Station 3, CH-1015 Lausanne, Switzerland
^bPhysics Institute, Space Research and Planetary Sciences, Center for Space and Habitability, University of Bern, Sidlerstrasse 5, 3012 Bern, Switzerland
^cUniversité de Bretagne Occidentale, Institut Universitaire Européen de la Mer, CNRS UMR 6538, Place Nicolas Copernic, 29280 Plouzané, France
^dSchool of Earth and Space Exploration, Arizona State University, PO Box 876004, Tempe, Arizona 85287, USA

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Reference
Clenet H, Jutzi M, Barrat J-A, Asphaug EI, Benz W and Gillet P (2014) A deep crust–mantle boundary in the asteroid 4 Vesta. Nature 511:303.
[doi:10.1038/nature13499]

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Christa Gall^a et al. (>10)*
*Find the extensive, full author and affiliation list on the publishers website.

^aDepartment of Physics and Astronomy, Aarhus University, Ny Munkegade 120, DK-8000 Aarhus C, Denmark

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Reference
Gall et al. (2014) Rapid formation of large dust grains in the luminous supernova 2010jl. Nature 511:326.
[doi:10.1038/nature13558]

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Michael Schäfer^a et al. (>10)*
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^aMax Planck Institute for Solar System Research, 37077 Göttingen, Germany

We produced two 1:250,000 scale geologic maps of the adjacent quadrangles Av-6 Gegania and Av-7 Lucaria, located in the equatorial region of (4) Vesta (0° E – 144° E, 22° S – 22° N). The mapping is based on clear and color filter images of the Framing Camera (FC) onboard the Dawn spacecraft, which has captured the entire illuminated surface of Vesta with high spatial resolution (up to ∼20 m/pixel), and on a digital terrain model derived from FC imagery. Besides the geologic mapping itself, a secondary purpose of this work is to investigate one of the most prominent morphological features on Vesta, namely the aggregation of several giant equatorial troughs termed the Divalia Fossae, most probably formed during the Rheasilvia impact near Vesta’s south pole. The up to 465 km long and 22 km wide troughs show height differences of up to 5 km between adjacent troughs and ridges. Another imprint of the Rheasilvia impact is the >350 km long and ∼250 km wide swath of ejecta crossing quadrangle Av-6 Gegania. This lobe shows a distinct appearance in FC color ratios and a high albedo in FC images, indicating a mineralogical similarity to material typically found within the Rheasilvia basin, in particular composed of diogenite-rich howardites. Almost the entire northern half of the mapping area shows the oldest surface, being dominated by upper crustal basaltic material. To the south, increasingly younger formations related to the Rheasilvia impact occur, either indicated by the troughs formed by Rheasilvia or by the Rheasilvia ejecta itself. Only medium sized impact craters with diameters less than 22 km occur within the two mapped quadrangles. Some of the craters exhibit ejecta blankets and/or distinctly dark or bright ejecta material in ejecta rays outside and exposures within the crater, and mass-wasting deposits down crater slopes, forming the youngest surfaces.

Reference
Schäfer et al. (in press) Imprint of the Rheasilvia Impact on Vesta – Geologic Mapping of Quadrangles Gegania and Lucaria. Icarus
[doi:10.1016/j.icarus.2014.06.026]
Copyright Elsevier

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M. P. Ronco and G. C. de Elía

Facultad de Ciencias Astronómicas y Geofísicas, Universidad Nacional de La Plata and Instituto de Astrofísica de La Plata, CCT La Plata-CONICET-UNLP, Paseo del Bosque S/N, 1900 La Plata, Argentina

Context. Several studies, observational and theoretical, suggest that planetary systems with only rocky planets are the most common in the Universe.
Aims. We study the diversity of planetary systems that might form around Sun-like stars in low-mass disks without gas-giant planets. We focus especially on the formation process of terrestrial planets in the habitable zone (HZ) and analyze their water contents with the goal to determine systems of astrobiological interest. In addition, we study the formation of planets on wide orbits because they can be detected with the microlensing technique.
Methods. N-body simulations of high resolution were developed for a wide range of surface density profiles. A bimodal distribution of planetesimals and planetary embryos with different physical and orbital configurations was used to simulate the planetary accretion process. The surface density profile combines a power law for the inside of the disk of the form r^−γ, with an exponential decay to the outside. We performed simulations adopting a disk of 0.03 M_⊙ and values of γ = 0.5, 1 and 1.5.
Results. All our simulations form planets in the HZ with different masses and final water contents depending on the three different profiles. For γ = 0.5, our simulations produce three planets in the HZ with masses ranging from 0.03 M_⊕ to 0.1 M_⊕ and water contents between 0.2 and 16 Earth oceans (1 Earth ocean =2.8 × 10^-4 M_⊕). For γ = 1, three planets form in the HZ with masses between 0.18 M_⊕ and 0.52 M_⊕ and water contents from 34 to 167 Earth oceans. Finally, for γ = 1.5, we find four planets in the HZ with masses ranging from 0.66 M_⊕ to 2.21 M_⊕ and water contents between 192 and 2326 Earth oceans. This profile shows distinctive results because it is the only one of those studied here that leads to the formation of water worlds.
Conclusions. Since planetary systems with γ = 1 and 1.5 present planets in the HZ with suitable masses to retain a long-lived atmosphere and to maintain plate tectonics, they seem to be the most promising candidates to be potentially habitable. Particularly, these systems form Earths and Super-Earths of at least 3 M_⊕ around the snow line, which can be discovered by the microlensing technique.

Reference
Ronco  MP and de Elía GC (2014) Diversity of planetary systems in low-mass disks:Terrestrial-type planet formation and water delivery. Astronomy & Astrophysics 567:A54.
[doi:10.1051/0004-6361/201323313]
Reproduced with permission © ESO

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