Megan E. Schwamb

Institute of Astronomy and Astrophysics, Academia Sinica, Taipei 10617, Taiwan.

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Reference
Schwamb ME (2014) Solar System: Stranded in no-man’s-land. Nature 507:435–436.
[doi:10.1038/507435a]

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Chadwick A. Trujillo¹ and Scott S. Sheppard²

¹Gemini Observatory, 670 North A‘ohoku Place, Hilo, Hawaii 96720, USA
²Department of Terrestrial Magnetism, Carnegie Institution for Science, 5241 Broad Branch Road NW, Washington DC 20015, USA

We do not have a copyright agreement with this publisher and cannot display the abstract here.

Reference
Trujillo CA and Sheppard SS (2014) A Sedna-like body with a perihelion of 80 astronomical units. Nature 507:471–474.
[doi:10.1038/nature13156]

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Aaron S. Burton¹, Daniel P. Glavin², Jamie E. Elsila², Jason P. Dworkin², Peter Jenniskens^3,4 and Qing-Zhu Yin⁵

¹NASA Johnson Space Center, Houston, Texas, USA
²NASA Goddard Space Flight Center, Greenbelt, Maryland, USA
³SETI Institute, Mountain View, California, USA
⁴NASA Ames Research Center, Moffett Field, California, USA
⁵Department of Earth and Planetary Sciences, University of California at Davis, Davis, California, USA

We determined the abundances and enantiomeric compositions of amino acids in Sutter’s Mill fragment #2 (designated SM2) recovered prior to heavy rains that fell April 25–26, 2012, and two other meteorite fragments, SM12 and SM51, that were recovered postrain. We also determined the abundance, enantiomeric, and isotopic compositions of amino acids in soil from the recovery site of fragment SM51. The three meteorite stones experienced terrestrial amino acid contamination, as evidenced by the low D/L ratios of several proteinogenic amino acids. The D/L ratios were higher in SM2 than in SM12 and SM51, consistent with rain introducing additional l-amino acid contaminants to SM12 and SM51. Higher percentages of glycine, β-alanine, and γ-amino-n-butyric acid were observed in free form in SM2 and SM51 compared with the soil, suggesting that these free amino acids may be indigenous. Trace levels of D+L-β-aminoisobutyric acid (β-AIB) observed in all three meteorites are not easily explained as terrestrial contamination, as β-AIB is rare on Earth and was not detected in the soil. Bulk carbon and nitrogen and isotopic ratios of the SM samples and the soil also indicate terrestrial contamination, as does compound-specific isotopic analysis of the amino acids in the soil. The amino acid abundances in SM2, the most pristine SM meteorite analyzed here, are approximately 20-fold lower than in the Murchison CM2 carbonaceous chondrite. This may be due to thermal metamorphism in the Sutter’s Mill parent body at temperatures greater than observed for other aqueously altered CM2 meteorites.

Reference
Burton AS, Glavin DP, Elsila JE, Dworkin JP, Jenniskens P and Yin Q-Z (in press) The amino acid composition of the Sutter’s Mill CM2 carbonaceous chondrite. Meteoritics & Planetary Science
[doi:10.1111/maps.12281]
Published by arrangement with John Wiley & Sons

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

^aINAF-IAPS Istituto di Astrofisica e Planetologia Spaziali, Via del Fosso del Cavaliere, 100, I-00133 Rome, Italy

Remote sensing data acquired during Dawn’s orbital mission at Vesta showed several local concentrations of high-albedo (bright) and low-albedo (dark) material units, in addition to spectrally distinct meteorite impact ejecta. The thermal behavior of such areas seen at local scale (1-10 km) is related to physical properties that can provide information about the origin of those materials. We use Dawn’s Visible and InfraRed (VIR) mapping spectrometer hyperspectral data to retrieve surface temperatures and emissivities, with high accuracy as long as temperatures are greater than 220 K. Some of the dark and bright features were observed multiple times by VIR in the various mission phases at variable spatial resolution, illumination and observation angles, local solar time, and heliocentric distance. This work presents the first temperature maps and spectral emissivities of several kilometer-scale dark and bright material units on Vesta. Results retrieved from the infrared data acquired by VIR show that bright regions generally correspond to regions with lower temperature, while dark regions correspond to areas with higher temperature. During maximum daily insolation and in the range of heliocentric distances explored by Dawn, i.e. 2.23-2.54 AU, the warmest dark unit found on Vesta rises to a temperature of 273 K, while bright units observed under comparable conditions do not exceed 266 K. Similarly, dark units appear to have higher emissivity on average compared to bright units. Dark-material units show a weak anticorrelation between temperature and albedo, whereas the relation is stronger for bright material units observed under the same conditions. Individual features may show either evanescent or distinct margins in the thermal images, as a consequence of the cohesion of the surface material. Finally, for the two categories of dark and bright materials, we were able to highlight the influence of heliocentric distance on surface temperatures, and estimate an average temperature rate change of 1% following a variation of 0.04 AU in the solar distance.

Reference
Tosi et al. (in press) Thermal measurements of dark and bright surface features on Vesta as derived from Dawn/VIR. Icarus
[doi:10.1016/j.icarus.2014.03.017]
Copyright Elsevier

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Gloria Delgado-Inglada^1,2 and Mónica Rodríguez¹

¹Instituto Nacional de Astrofísica, Óptica y Electrónica (INAOE), Apdo. Postal 51 y 216, 72000 Puebla, Pue., Mexico
²Instituto de Astronomía, Universidad Nacional Autónoma de México, Apdo. Postal 70264,04510, México D. F., Mexico

We study the dust present in 56 Galactic planetary nebulae (PNe) through their iron depletion factors, their C/O abundance ratios (in 51 objects), and the dust features that appear in their infrared spectra (for 33 objects). Our sample objects have deep optical spectra of good quality, and most of them also have ultraviolet observations. We use these observations to derive the iron abundances and the C/O abundance ratios in a homogeneous way for all the objects. We compile detections of infrared dust features from the literature and we analyze the available Spitzer/IRS spectra. Most of the PNe have C/O ratios below one and show crystalline silicates in their infrared spectra. The PNe with silicates have C/O <1, with the exception of Cn 1-5. Most of the PNe with dust features related to C-rich environments (SiC or the 30 μm feature usually associated to MgS) have C/O  0.8. Polycyclic aromatic hydrocarbons are detected over the full range of C/O values, including 6 objects that also show silicates. Iron abundances are low in all the objects, implying that more than 90% of their iron atoms are deposited into dust grains. The range of iron depletions in the sample covers about two orders of magnitude, and we find that the highest depletion factors are found in C-rich objects with SiC or the 30 μm feature in their infrared spectra, whereas some of the O-rich objects with silicates show the lowest depletion factors.

Reference
Delgado-Inglada G and Mónica Rodríguez M (2014) C/O Abundance Ratios, Iron Depletions, and Infrared Dust Features in Galactic Planetary Nebulae. The Astrophysical Journal 784:173.
[doi:10.1088/0004-637X/784/2/173]

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E. E. Hardegree-Ullman^1,2, M. S. Gudipati^3,4, A. C. A. Boogert^2,5, H. Lignell^6,7, L. J. Allamandola⁸, K. R. Stapelfeldt⁹ and M. Werner³

¹New York Center for Astrobiology and Department of Physics, Applied Physics, and Astronomy, Rensselaer Polytechnic Institute, 110 8th Street, Troy, NY 12180, USA
²Infrared Processing and Analysis Center, Mail Code 100-22, California Institute of Technology, Pasadena, CA 91125, USA
³Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109, USA
⁴IPST, University of Maryland, College Park, MD 20742, USA
⁵SOFIA Science Center, USRA, NASA Ames Research Center, M.S. N232-12, Moffett Field, CA 94035, USA
⁶Department of Chemistry, University of California Irvine, Irvine, CA 92697-2025, USA
⁷Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, CA 91125, USA
⁸Space Science Division, Mail Stop 245-6, NASA Ames Research Center, Moffett Field, CA 94035, USA
⁹NASA Goddard Space Flight Center, Exoplanets and Stellar Astrophysics Laboratory, Code 667, Greenbelt, MD 20771, USA

Broad infrared emission features (e.g., at 3.3, 6.2, 7.7, 8.6, and 11.3 μm) from the gas phase interstellar medium have long been attributed to polycyclic aromatic hydrocarbons (PAHs). A significant portion (10%–20%) of the Milky Way’s carbon reservoir is locked in PAH molecules, which makes their characterization integral to our understanding of astrochemistry. In molecular clouds and the dense envelopes and disks of young stellar objects (YSOs), PAHs are expected to be frozen in the icy mantles of dust grains where they should reveal themselves through infrared absorption. To facilitate the search for frozen interstellar PAHs, laboratory experiments were conducted to determine the positions and strengths of the bands of pyrene mixed with H₂O and D₂O ices. The D₂O mixtures are used to measure pyrene bands that are masked by the strong bands of H₂O, leading to the first laboratory determination of the band strength for the CH stretching mode of pyrene in water ice near 3.25 μm. Our infrared band strengths were normalized to experimentally determined ultraviolet band strengths, and we find that they are generally ~50% larger than those reported by Bouwman et al. based on theoretical strengths. These improved band strengths were used to reexamine YSO spectra published by Boogert et al. to estimate the contribution of frozen PAHs to absorption in the 5–8 μm spectral region, taking into account the strength of the 3.25 μm CH stretching mode. It is found that frozen neutral PAHs contain 5%–9% of the cosmic carbon budget and account for 2%–9% of the unidentified absorption in the 5–8 μm region.

Reference
Hardegree-Ullman EE, Gudipati MS, Boogert ACA, Lignell H, Allamandola LJ, Stapelfeldt KR and Werner M (2014) Laboratory Determination of the Infrared Band Strengths of Pyrene Frozen in Water Ice: Implications for the Composition of Interstellar Ices. The Astrophysical Journal 784:172.
[doi:10.1088/0004-637X/784/2/172]

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