Julien Stodolna, Zack Gainsforth, Anna L. Butterworth and Andrew J. Westphal

Space Sciences Laboratory, University of California, Berkeley, 7 Gauss Way, Berkeley, CA 94720, USA

We report the presence of preserved primitive fine-grained material containing an enstatite whisker with the crystallographic characteristics of a primary condensate in a sample of the Jupiter-family comet Wild 2, returned to earth by NASAʼs Stardust mission. The preserved primitive material is composed of silica-rich amorphous material embedded with iron sulfides and silicates. It is in close association with a type II chondrule-like object in the track C2052,2,74 (Ogliore et al., 2012). The close association of a chondrule and a primary condensate shows they must have formed in different environments and probably met in the comet-forming region. The first observation of an enstatite whisker with properties indicating primary condensation in a comet is a new link between comets and Chondritic Porous IDPs (CP-IDPs).

Reference
Stodolna J, Gainsforth Z, Butterworth AL and Westphal AJ (2014) Characterization of preserved primitive fine-grained material from the Jupiter family comet 81P/Wild 2 – A new link between comets and CP-IDPs. Earth and Planetary Science Letters 388:367–373.
[doi:10.1016/j.epsl.2013.12.018]
Copyright Elsevier

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José M. Madiedo^a,b, José L. Ortiz^c, Josep M. Trigo-Rodríguez^d, Joan Dergham^d, Alberto J. Castro-Tirado^c, Jesús Cabrera-Caño^b, Pep Pujols^e

^aFacultad de Física. Departamento de Física Atómica, Molecular y Nuclear. Universidad de Sevilla, 4012 Sevilla, Spain
^bFacultad de Ciencias Experimentales. Universidad de Huelva, 21071 Huelva, Spain
^cInstituto de Astrofísica de Andalucía, CSIC, Apt. 3004, Camino Bajo de Huetor 50, 18080 Granada, Spain
^dInstitute of Space Sciences (CSIC-IEEC), Campus UAB, Facultat de Ciències, Torre C5-parell-2ª, 08193 Bellaterra, Barcelona, Spain
^eGrup d’Estudis Astronòmics (GEA) and Agrupació Astronòmica d’Osona, Barcelona, Spain

We present the analysis of five bright fireballs observed over Spain and France between 2010 and 2012. Their absolute magnitude ranged between -9.0 and -11.5. Radiant and orbital data indicate that these events were associated with the Taurid meteoroid stream. Their trajectory in the atmosphere is calculated and the heliocentric orbit of the meteoroids is obtained. The emission spectra produced by three of these fireballs are also discussed, and the chemical nature of the parent impactors is inferred, together with different physical parameters of these particles such as the meteoroid mass and tensile strength. On the basis of these results, the ability of Taurid meteoroids to produce meteorites is discussed.

Reference
Madiedo JM, Ortiz JL, Trigo-Rodríguez JM, Dergham J, Castro-Tirado AJ, Cabrera-Caño J and Pujols P (in press) Analysis of bright Taurid fireballs and their ability to produce meteorites. Icarus
[doi:10.1016/j.icarus.2013.12.025]
Copyright Elsevier

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Arya Udry*, J. Brian Balta, Harry Y. McSween Jr.

Planetary Geosciences Institute, Department of Earth and Planetary Sciences, University of Tennessee, Knoxville, Tennessee, USA

Martian primary compositions, i.e., magmas that did not experience fractionation and/or contamination after extraction from the mantle, occur as a subset of Martian meteorites and a few lavas analyzed on the planet’s surface by rovers. Eruptions of primary magmas are rare on Earth and presumably on Mars. Previous studies of fractional crystallization of Martian primary magmas have been conducted under isobaric conditions, simulating idealized crystallization in magma chambers. Polybaric fractionation, which occurs during magma ascent, has not been investigated in detail for Martian magmas. Using the MELTS algorithm and the pMELTS revision, we present comprehensive isobaric and polybaric thermodynamic calculations of the fractional crystallization of four primary or parental Martian magmas (Humphrey, Fastball, Y-980459 shergottite, and nakhlite parental melts) using various pressure-temperature paths, oxygen fugacities, and water contents to constrain how these magmas might evolve. We then examine whether known Martian alkaline rock compositions could have formed through fractional crystallization of these magmas under the simulated conditions. We find that isobaric and polybaric crystallization paths produce similar residual melt compositions, but given sufficient details, we may be able to distinguish between them. We calculate that Backstay (Gusev Crater) likely formed by fractionation of a primary magma under polybaric conditions, while Jake_M (Gale Crater) may have formed through melting of a metasomatized mantle, crustal assimilation, or fractional crystallization of an unknown primary magma. The best fits for the Backstay composition indicate that consideration of polybaric crystallization paths can help improve the quality of fit when simulating liquid lines of descent.

Reference
Udry A, Balta JB and McSween Jr. HY (in press) Exploring fractionation models for Martian magmas. Journal of Geophysical Research: Planets
[doi:10.1002/2013JE004445]
Published by arrangement with John Wiley & Sons

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