Ritesh Kumar Mishra^a,b and Marc Chaussidon^a,c

^aCentre de Recherches Pétrographiques et Géochimiques, Boite Postale 20, 15 Rue du Notre Dame des Pauvres, INSU-CNRS, Université de Lorraine, 54501 Vandoeuvre-lès-Nancy, France
^bPhysical Reseach Laboratory, Navrangpura, Ahmedabad 380009, Gujarat, India1
^cInstitut de Physique du Globe de Paris, Université Paris-Diderot, CNRS (UMR 7154), PRES Sorbonne Paris Cité, 1 rue Jussieu, 75005 Paris, France1

The short-lived now-extinct nuclide (SLN) ⁶⁰Fe, which decays to ⁶⁰Ni with a half-life of 2.62 Ma, is uniquely of stellar origin. Hence, its Solar System initial abundance yields information about the source of SLNs and the astrophysical environment in which the Solar System was born. Only a few chondrules (∼19) from unequilibrated ordinary chondrites have reported resolved ⁶⁰Ni excesses using in situ secondary ion mass spectrometry implying  in the early Solar System, and among these very few (3) have higher excesses implying  (Mishra et al., 2010, Mishra and Goswami, 2014 and Telus et al., 2012). At variance, multi-collector inductively coupled plasma mass spectrometer studies of bulk samples and mineral separates from differentiated meteorites, angrites, achondrites, and chondrules suggest a low abundance of ⁶⁰Fe/⁵⁶Fe of ∼1.4×10⁻⁸ which would rule out the need for an external seeding of the early Solar with stellar ⁶⁰Fe (Quitté et al., 2011 and Tang and Dauphas, 2012). Two Semarkona chondrules and one Efremovka chondrule analyzed in the present study have mass fractionation corrected excess of up to ∼75 permil (‰) and give ⁶⁰Fe isochrons with initial ⁶⁰Fe/⁵⁶Fe ratios of(7.8±3.7)×10⁻⁷, (3.8±1.6)×10⁻⁷, and (2.2±1.1)×10⁻⁷ (2σ), for Efremovka Ch 1, Semarkona Ch 12, and Semarkona Ch J5 respectively. The higher values of ⁶⁰Fe/⁵⁶Fe ratios seen in the chondrules of these least altered meteorites samples concur with and lend greater credence to the suggestion of a massive star as the source of ⁶⁰Fe, and possibly of other short-lived nuclides, to the early Solar System. However, no definitive explanation (e.g. sample bias, effects of metamorphism, ⁶⁰Fe heterogeneity) to the apparent disagreement with studies of bulk chondrules and chondrule fragments has been found.

Reference
Mishra RK and Chaussidon M (in press) Fossil records of high level of 60Fe in chondrules from unequilibrated chondrites. Earth and Planetary Science Letters 398:90–100.
[doi:10.1016/j.epsl.2014.04.032]
Copyright Elsevier

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Eric Hand

Planetary scientists have begun to plan the first stage of a Mars sample return mission: a rover to be launched in 2020. Scientists want the rover to drill at least 31 rock samples weighing about 15 grams apiece during its 2-year mission and pack them in a cache that a later mission will retrieve. But the rover will have to work faster than the current rover, Curiosity, which has drilled just three samples in its 20 months on Mars.

Reference
Hand E (2014) NASA planners gear up for martian sample return. Science 344:787-788.
[doi:10.1126/science.344.6186.787]
Reprinted with permission from AAAS

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M. Darby Dyar¹ et al. (>10)*
*Find the extensive, full author and affiliation list on the publishers website.

¹Department of Astronomy, Mount Holyoke College, South Hadley, Massachusetts 01075, U.S.A.

Phosphate minerals, while relatively rare, show a broad range of crystal structure types with linkages among PO₄ tetrahedra mimicking the hierarchy of polymerization of SiO₄ tetrahedra seen in silicate minerals. To augment previous Mössbauer studies of individual phosphate species and groups of species, this paper presents new Mössbauer data on 63 different phosphate samples, and integrates them with data on more than 37 phosphate species in 62 other studies from the literature. Variations in Mössbauer parameters of different sites in each mineral are then related to both the local polyhedral environment around the Fe cations and the overall structural characteristics of each species. The entire aggregated Mössbauer data set on phosphate minerals is juxtaposed against parameters obtained for spectra from the MIMOS spectrometers on Mars. This comparison demonstrates that signatures from many different phosphate or sulfate mineral species could also be contributing to Mars Mössbauer spectra. Results underscore the conclusion that unique mineral identifications are generally not possible from Mössbauer data alone, particularly for paramagnetic phases, although combining Mössbauer results with other data sets enables a greater level of confidence in constraining mineralogy. This study provides a wealth of new data on Fe-bearing phosphate minerals to bolster future analyses of Mössbauer spectra acquired on Mars.

Reference
Dyar et al. (2014) Mössbauer parameters of iron in phosphate minerals: Implications for interpretation of martian data. American Mineralogist 99:914-942.
[doi:10.2138/am.2014.4701]
Copyright: The Mineralogical Society of America

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P. Riviere-Marichalar^1,2 et al. (>10)*
*Find the extensive, full author and affiliation list on the publishers website.

¹ Centro de Astrobiología (INTA–CSIC) – Depto. Astrofísica, POB 78, ESAC Campus, 28691 Villanueva de la Cañada, Spain 
² Kapteyn Astronomical Institute, PO Box 800, 9700 AV Groningen, The Netherlands

Context. Debris discs are thought to be formed through the collisional grinding of planetesimals, and then can be considered as the outcome of planet formation. Understanding the properties of gas and dust in debris discs can help us comprehend the architecture of extrasolar planetary systems. Herschel Space Observatory far-infrared (IR) photometry and spectroscopy have provided a valuable dataset for the study of debris discs gas and dust composition. This paper is part of a series of papers devoted to the study of Herschel-PACS observations of young stellar associations.
Aims. This work aims at studying the properties of discs in the beta Pictoris moving group (BPMG) through far-IR PACS observations of dust and gas.
Methods. We obtained Herschel-PACS far-IR photometric observations at 70, 100, and 160 μm of 19 BPMG members, together with spectroscopic observations for four of them. These observations were centred at 63.18 μm and 157 μm, aiming to detect [OI] and [CII] emission. We incorporated the new far-IR observations in the SED of BPMG members and fitted modified blackbody models to better characterise the dust content.
Results. We have detected far-IR excess emission towards nine BPMG members, including the first detection of an IR excess towards HD 29391.The star HD 172555, shows [OI] emission, while HD 181296 shows [CII] emission, expanding the short list of debris discs with a gas detection. No debris disc in BPMG is detected in both [OI] and [CII]. The discs show dust temperatures in the range 55–264 K, with low dust masses (<6.6 × 10^-5 M_⊕ to 0.2 M_⊕) and radii from blackbody models in the range 3 to ~82 AU. All the objects with a gas detection are early spectral type stars with a hot dust component.

Reference
Riviere-Marichalar et al. (2014) Gas and dust in the beta Pictoris moving group as seen by the Herschel Space Observatory. Astronomy & Astrophysics 565:A68.
[doi:10.1051/0004-6361/201322901]
Reproduced with permission © ESO

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