José M. Madiedo^a,b et al. (>10)*
*Find the extensive, full author and affiliation list on the publishers website.

^aDepartamento de Física Atómica, Molecular y Nuclear. Facultad de Física. Universidad de Sevilla. 41012 Sevilla, Spain
^bFacultad de Ciencias Experimentales, Universidad de Huelva, 21071 Huelva, Spain

Among the most astonishing astronomical phenomena are the extremely bright bolides produced by the entry of large meteoroids into the Earth’s atmosphere. These events are rare and unexpected because current telescopic surveys are still missing meter-sized meteoroids, particularly those of dark nature and presumably cometary origin. In this work we present the analysis of two very bright fireballs of such origin recently observed over Spain. The first of these was recorded on September 25, 2010, while the second one took place on August 23, 2012. With an absolute magnitude of -18 and -17, respectively, these sporadic events fall within the superbolide category. Their atmospheric trajectory is calculated, together with the heliocentric orbit of the parent meteoroids. Other physical properties of these particles are estimated, such as their preatmospheric mass and tensile strength. The emission spectrum recorded for one of these events is also discussed. Our analysis indicates that none of these superbolides was a meteorite-dropping event. From their orbital parameters, a cometary nature for the parent meteoroids is inferred.

Reference
José M. Madiedo et al. (in press) Analysis of two superbolides with a cometary origin observed over the iberian peninsula. Icarus
[doi:10.1016/j.icarus.2014.01.031]
Copyright Elsevier

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Amaury Thiabaud^1,2, Ulysse Marboeuf^1,2, Yann Alibert^1,2,3, Nahuel Cabral^1,2, Ingo Leya^1,2 and Klaus Mezger^1,4

¹Center for Space and Habitability, Universität Bern, 3012 Bern, Switzerland
²Physikalisches Institut, Universität Bern, 3012 Bern, Switzerland
³Observatoire de Besançon, 41 avenue de l’Observatoire, 25000 Besançon, France
⁴Institut für Geologie, Universität Bern, 3012 Bern, Switzerland

Context. To date, calculations of planet formation have mainly focused on dynamics, and only a few have considered the chemical composition of refractory elements and compounds in the planetary bodies. While many studies have been concentrating on the chemical composition of volatile compounds (such as H₂O, CO, CO₂) incorporated in planets, only a few have considered the refractory materials as well, although they are of great importance for the formation of rocky planets.
Aims. We computed the abundance of refractory elements in planetary bodies formed in stellar systems with a solar chemical composition by combining models of chemical composition and planet formation. We also considered the formation of refractory organic compounds, which have been ignored in previous studies on this topic.
Methods. We used the commercial software package HSC Chemistry to compute the condensation sequence and chemical composition of refractory minerals incorporated into planets. The problem of refractory organic material is approached with two distinct model calculations: the first considers that the fraction of atoms used in the formation of organic compounds is removed from the system (i.e., organic compounds are formed in the gas phase and are non-reactive); and the second assumes that organic compounds are formed by the reaction between different compounds that had previously condensed from the gas phase.
Results. Results show that refractory material represents more than 50 wt % of the mass of solids accreted by the simulated planets with up to 30 wt % of the total mass composed of refractory organic compounds. Carbide and silicate abundances are consistent with C/O and Mg/Si elemental ratios of 0.5 and 1.02 for the Sun. Less than 1 wt % of carbides are present in the planets, and pyroxene and olivine are formed in similar quantities. The model predicts planets that are similar in composition to those of the solar system. Starting from a common initial nebula composition, it also shows that a wide variety of chemically different planets can form, which means that the differences in planetary compositions are due to differences in the planetary formation process.
Conclusions. We show that a model in which refractory organic material is absent from the system is more compatible with observations. The use of a planet formation model is essential to form a wide diversity of planets in a consistent way.

Reference
Losiak A, Wild EM, Michlmayr L and Koeberl C (in press) From stellar nebula to planets: The refractory components. Astronomy & Astrophysics 562:A27.
[doi:10.1051/0004-6361/201322208]
Reproduced with permission © ESO

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John P. Bradley^a,b, Hope A. Ishii^a,b, Jeffrey J. Gillis-Davis^b, James Ciston^c, Michael H. Nielsen^d,e, Hans A. Bechtel^f, and Michael C. Martin^f

^aInstitute of Geophysics and Planetary Physics, Lawrence Livermore National Laboratory, Livermore, CA 94550;
^bHawaii Institute of Geophysics and Planetology, University of Hawaii at Manoa, Honolulu, HI 96822;
^cNational Center for Electron Microscopy,
^dMaterials Science Division, and
^eAdvanced Light Source Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720; and
^fDepartment of Materials Science and Engineering, University of California, Berkeley, CA 94720

The solar wind (SW), composed of predominantly ~1-keV H⁺ ions, produces amorphous rims up to ∼150 nm thick on the surfaces of minerals exposed in space. Silicates with amorphous rims are observed on interplanetary dust particles and on lunar and asteroid soil regolith grains. Implanted H⁺ may react with oxygen in the minerals to form trace amounts of hydroxyl (−OH) and/or water (H₂O). Previous studies have detected hydroxyl in lunar soils, but its chemical state, physical location in the soils, and source(s) are debated. If −OH or H₂O is generated in rims on silicate grains, there are important implications for the origins of water in the solar system and other astrophysical environments. By exploiting the high spatial resolution of transmission electron microscopy and valence electron energy-loss spectroscopy, we detect water sealed in vesicles within amorphous rims produced by SW irradiation of silicate mineral grains on the exterior surfaces of interplanetary dust particles. Our findings establish that water is a byproduct of SW space weathering. We conclude, on the basis of the pervasiveness of the SW and silicate materials, that the production of radiolytic SW water on airless bodies is a ubiquitous process throughout the solar system.

Reference
Bradley JP, Ishii HA, Gillis-Davis JJ, Ciston J, Nielsen MH, Bechtel HA and Martin MC (in press) Detection of solar wind-produced water in irradiated rims on silicate minerals. PNAS 111:1732–1735.
[doi:10.1073/pnas.1320115111]

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