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

^aDepartment of Physics, Lund University, Lund, Sweden
^bHawai’i Institute of Geophysics and Planetology, University of Hawai’i at Manoa, Honolulu, HI, USA

About a quarter of all meteorites falling on Earth today originate from the breakup of the L-chondrite parent body ~470 Ma ago, the largest documented breakup in the asteroid belt in the past ~3 Ga. A window into the flux of meteorites to Earth shortly after this event comes from the recovery of about 100 fossil L chondrites (1–21 cm in diameter) in a quarry of mid-Ordovician limestone in southern Sweden. Here we report on the first non-L-chondritic meteorite from the quarry, an 8 cm large winonaite-related meteorite of a type not known among present-day meteorite falls and finds. The noble gas data for relict spinels recovered from the meteorite show that it may be a remnant of the body that hit and broke up the L-chondrite parent body, creating one of the major asteroid families in the asteroid belt. After two decades of systematic recovery of fossil meteorites and relict extraterrestrial spinel grains from marine limestone, it appears that the meteorite flux to Earth in the mid-Ordovician was very different from that of today.

Reference
Schmitz et al. (in press) A fossil winonaite-like meteorite in Ordovician limestone: A piece of the impactor that broke up the L-chondrite parent body? Earth and Planetary Science Letters 400:145.
[doi:10.1016/j.epsl.2014.05.034]
Copyright Elsevier

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Derek W. G. Sears

Space Science and Astrobiology Division, NASA Ames Research Center/BAER Institute, Mountain View, California, USA

In this interview, William Hartmann (Bill, Fig. 1) describes how he was inspired as a teenager by a map of the Moon in an encyclopedia and by the paintings by Chesley Bonestell. Through the amateur journal “Strolling Astronomer,” he shared his interests with other teenagers who became lifelong colleagues. At college, he participated in Project Moonwatch, observing early artificial satellites. In graduate school, under Gerard Kuiper, Bill discovered Mare Orientale and other large concentric lunar basin structures. In the 1960s and 1970s, he used crater densities to study surface ages and erosive/depositional effects, predicted the approximately 3.6 Gyr ages of the lunar maria before the Apollo samples, discovered the intense pre-mare lunar bombardment, deduced the youthful Martian volcanism as part of the Mariner 9 team, and proposed (with Don Davis) the giant impact model for lunar origin. In 1972, he helped found (what is now) the Planetary Science Institute. From the late 1970s to early 1990s, Bill worked mostly with Dale Cruikshank and Dave Tholen at Mauna Kea Observatory, helping to break down the Victorian paradigm that separated comets and asteroids, and determining the approximately 4% albedo of comet nuclei. Most recently, Bill has worked with the imaging teams for several additional Mars missions. He has written three college textbooks and, since the 1970s, after painting illustrations for his textbooks, has devoted part of his time to painting, having had several exhibitions. He has also published two novels. Bill Hartmann won the 2010 Barringer Award for impact studies and the first Carl Sagan Award for outreach in 1997.

Reference
Sears DWG (in press) Oral histories in meteoritics and planetary science—XXIV: William K. Hartmann. Meteoritics & Planetary Science
[doi:10.1111/maps.12298]
Published by arrangement with John Wiley & Sons

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Norbert Schorghofer¹ and Oded Aharonson²

¹Institute for Astronomy and NASA Astrobiology Institute, University of Hawaii, Honolulu, HI 96822, USA
²Helen Kimmel Center for Planetary Science, Department of Earth and Planetary Sciences, Weizmann Institute of Science, Rehovot, 76100, Israel

It has long been suggested that water ice can exist in extremely cold regions near the lunar poles, where sublimation loss is negligible. The geographic distribution of H-bearing regolith shows only a partial or ambiguous correlation with permanently shadowed areas, thus suggesting that another mechanism may contribute to locally enhancing water concentrations. We show that under suitable conditions, water molecules can be pumped down into the regolith by day-night temperature cycles, leading to an enrichment of H₂O in excess of the surface concentration. Ideal conditions for pumping are estimated and found to occur where the mean surface temperature is below 105 K and the peak surface temperature is above 120 K. These conditions complement those of the classical cold traps that are roughly defined by peak temperatures lower than 120 K. On the present-day Moon, an estimated 0.8% of the global surface area experiences such temperature variations. Typically, pumping occurs on pole-facing slopes in small areas, but within a few degrees of each pole the equator-facing slopes are preferred. Although pumping of water molecules is expected over cumulatively large areas, the absolute yield of this pump is low; at best, a few percent of the H₂O delivered to the surface could have accumulated in the near-surface layer in this way. The amount of ice increases with vapor diffusivity and is thus higher in the regolith with large pore spaces.

Reference
Schorghofer N and Aharonson O (2014) The Lunar Thermal Ice Pump. The Astrophysical Journal 788:169.
[doi:10.1088/0004-637X/788/2/169]

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M. Rubin¹, N. Fougere², K. Altwegg^1,3, M. R. Combi², L. Le Roy³, V. M. Tenishev² and N. Thomas^1,3

¹Physikalisches Institut, University of Bern, Sidlerstrasse 5, 3012 Bern, Switzerland
²Atmospheric, Oceanic and Space Sciences, University of Michigan, 2455 Hayward Street, Ann Arbor, MI 48109, USA
³Center for Space and Habitability, University of Bern, Sidlerstrasse 5, 3012 Bern, Switzerland

Comets are surrounded by a thin expanding atmosphere, and although the nucleus’ gravity is small, some molecules and grains, possibly with the inclusion of ices, can get transported around the nucleus through scattering (atoms/molecules) and gravitational pull (grains). Based on the obliquity of the comet, it is also possible that volatile material and icy grains get trapped in regions, which are in shadow until the comet passes its equinox. When the Sun rises above the horizon and the surface starts to heat up, this condensed material starts to desorb and icy grains will sublimate off the surface, possibly increasing the comet’s neutral gas production rate on the outbound path. In this paper we investigate the mass transport around the nucleus, and based on a simplified model, we derive the possible contribution to the asymmetry in the seasonal gas production rate that could arise from trapped material released from cold areas once they come into sunlight. We conclude that the total amount of volatiles retained by this effect can only contribute up to a few percent of the asymmetry observed in some comets.

Reference
Rubin M, Fougere N, Altwegg K, Combi MR, Le Roy L, Tenishev VM and Thomas N (in press) Mass Transport around Comets and its Impact on the Seasonal Differences in Water Production Rates. The Astrophysical Journal 788:168.
[doi:10.1088/0004-637X/788/2/168]

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Gregor J. Golabek^1,2, Bernard Bourdon² and Taras V. Gerya¹

¹ETH Zurich, Institute of Geophysics, Zurich, Switzerland
²Laboratoire de Géologie de Lyon, ENS Lyon, CNRS and Université Claude Bernard de Lyon, Lyon Cedex 07, France

The acapulcoite-lodranite meteorites are members of the primitive achondrite class. The observation of partial melting and resulting partial removal of Fe-FeS indicates that this meteorite group could be an important link between achondrite and iron meteorites, on the one hand, and chondrite meteorites, on the other. Thus, a better understanding of the thermomechanical evolution of the parent body of this meteorite group can help improve our understanding of the evolution of early planetesimals. Here, we use 2-D and 3-D finite-difference numerical models to determine the formation time, initial radius of the parent body of the acapulcoite-lodranite meteorites, and their formation depth inside the body by applying available geochronological, thermal, and textural constraints to our numerical data. Our results indicate that the best fit to the data can be obtained for a parent body with 25–65 km radius, which formed around 1.3 Ma after calcium-aluminum-rich inclusions. The 2-D and 3-D results considering various initial temperatures and the effect of porosity indicate possible formation depths of the acapulcoite-lodranite meteorites of 9–19 and 14–25 km, respectively. Our data also suggest that other meteorite classes could form at different depths inside the same parent body, supporting recently proposed models (Elkins-Tanton et al. 2011; Weiss and Elkins-Tanton2013).

Reference
Golabek GJ, Bourdon B and Gerya TV (in press) Numerical models of the thermomechanical evolution of planetesimals: Application to the acapulcoite-lodranite parent body. Meteoritics & Planetary Science
[doi:10.1111/maps.12302]
Published by arrangement with John Wiley & Sons

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Steven J. Jaret^1,†, Linda C. Kah¹ and R. Scott Harris^2,3

¹Department of Earth & Planetary Sciences, University of Tennessee, Knoxville, Tennessee, USA
²Department of Geological Sciences, Brown University, Providence, Rhode Island, USA
³Georgia Department of Transportation, Office of Materials and Testing, Forest Park, Georgia, USA
^††Department of Geosciences, Stony Brook University, Stony Brook, New York, USA

The Tenoumer impact structure is a small, well-preserved crater within Archean to Paleoproterozoic amphibolite, gneiss, and granite of the Reguibat Shield, north-central Mauritania. The structure is surrounded by a thin ejecta blanket of crystalline blocks (granitic gneiss, granite, and amphibolite) and impact-melt rocks. Evidence of shock metamorphism of quartz, most notably planar deformation features (PDFs), occurs exclusively in granitic clasts entrained within small bodies of polymict, glass-rich breccia. Impact-related deformation features in oligoclase and microcline grains, on the other hand, occur both within clasts in melt-breccia deposits, where they co-occur with quartz PDFs, and also within melt-free crystalline ejecta, in the absence of co-occurring quartz PDFs. Feldspar deformation features include multiple orientations of PDFs, enhanced optical relief of grain components, selective disordering of alternate twins, inclined lamellae within alternate twins, and combinations of these individual textures. The distribution of shock features in quartz and feldspar suggests that deformation textures within feldspar can record a wide range of average pressures, starting below that required for shock deformation of quartz. We suggest that experimental analysis of feldspar behavior, combined with detailed mapping of shock metamorphism of feldspar in natural systems, may provide critical data to constrain energy dissipation within impact regimes that experienced low average shock pressures.

Reference
Jaret SJ, Kah LC and Harris RS (in press) Progressive deformation of feldspar recording low-barometry impact processes, Tenoumer impact structure, Mauritania. Meteoritics & Planetary Science
[doi:10.1111/maps.12310]
Published by arrangement with John Wiley & Sons

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Nan Liu^1,2,3, Roberto Gallino⁴, Sara Bisterzo^4,5, Andrew M. Davis^1,2,6, Michael R. Savina^2,3, and Michael J. Pellin^1,2,3,6

¹Department of the Geophysical Sciences, The University of Chicago, Chicago, IL 60637, USA
²Chicago Center for Cosmochemistry, Chicago, IL 60637, USA
³Materials Science Division, Argonne National Laboratory, Argonne, IL 60439, USA
⁴Dipartimento di Fisica, Università di Torino, Torino I-10125, Italy
⁵INAF-Osservatorio Astrofisico di Torino-Strada Osservatorio 20, Pino Torinese I-10025, Italy
⁶Enrico Fermi Institute, The University of Chicago, Chicago, IL 60637, USA

We present postprocess asymptotic giant branch (AGB) nucleosynthesis models with different ¹³C-pocket internal structures to better explain zirconium isotope measurements in mainstream presolar SiC grains by Nicolussi et al. and Barzyk et al. We show that higher-than-solar ⁹²Zr/⁹⁴Zr ratios can be predicted by adopting a ¹³C-pocket with a flat ¹³C profile, instead of the previous decreasing-with-depth ¹³C profile. The improved agreement between grain data for zirconium isotopes and AGB models provides additional support for a recent proposal of a flat ¹³C profile based on barium isotopes in mainstream SiC grains by Liu et al.

Reference
Liu N, Gallino R, Bisterzo S, Davis AM, Savina MR and Pellin MJ (in press) The 13C-Pocket Structure in AGB Models: Constraints from Zirconium Isotope Abundances in Single Mainstream SiC Grains. The Astrophysical Journal Letters 788:163.
[doi:10.1088/0004-637X/788/2/163]

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Jaime E. Pineda¹, Sascha P. Quanz¹, Farzana Meru¹, Gijs D. Mulders², Michael R. Meyer¹, Olja Panić³ and Henning Avenhaus¹

¹Institute for Astronomy, ETH Zurich, Wolfgang-Pauli-Strasse 27, CH-8093 Zurich, Switzerland
²Lunar and Planetary Laboratory, The University of Arizona, 1629 E. University Blvd., Tucson, AZ 85721, USA
³Institute of Astronomy, Madingley Road, Cambridge CB3 0HA, UK

The disk around the Herbig Ae/Be star HD 100546 has been extensively studied and it is one of the systems for which there are observational indications of ongoing and/or recent planet formation. However, up until now, no resolved image of the millimeter dust emission or the gas has been published. We present the first resolved images of the disk around HD 100546 obtained in Band 7 with the ALMA observatory. The CO (3-2) image reveals a gas disk that extends out to 350 au radius at the 3σ level. Surprisingly, the 870 μm dust continuum emission is compact (radius <60 au) and asymmetric. The dust emission is well matched by a truncated disk with an outer radius of 50 au. The lack of millimeter-sized particles outside 60 au is consistent with radial drift of particles of this size. The protoplanet candidate, identified in previous high-contrast NACO/VLT L‘ observations, could be related to the sharp outer edge of the millimeter-sized particles. Future higher angular resolution ALMA observations are needed to determine the detailed properties of the millimeter emission and the gas kinematics in the inner region (<2”). Such observations could also reveal the presence of a planet through the detection of circumplanetary disk material.

Reference
Pineda JE, Quanz SP, Meru F, Mulders GD, Meyer MR, Panić O and Avenhaus H (in press) Resolved Images of the Protoplanetary Disk around HD 100546 with ALMA. The Astrophysical Journal Letters
[doi:10.1088/2041-8205/788/2/L34]

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K. Nishiizumi¹, M. W. Caffee², Y. Hamajima³, R. C. Reedy⁴ and K. C. Welten¹

¹Space Sciences Laboratory, University of California, Berkeley, California, USA
²Department of Physics, Purdue University, West Lafayette, Indiana, USA
³Low Level Radioactivity Laboratory, Kanazawa University, Nomi, Ishikawa, Japan
⁴Planetary Science Institute, Los Alamos, New Mexico, USA

The Sutter’s Mill (SM) carbonaceous chondrite fell in California on April 22, 2012. The cosmogenic radionuclide data indicate that Sutter’s Mill was exposed to cosmic rays for 0.082 ± 0.008 Myr, which is one of the shortest ages for C chondrites, but overlaps with a small cluster at approximately 0.1 Myr. The age is significantly longer than proposed ages that were obtained from cosmogenic noble gas concentrations, which have large uncertainties due to trapped noble gas corrections. The presence of neutron-capture ⁶⁰Co and ³⁶Cl in SM indicates a minimum preatmospheric radius of approximately 50 cm, and is consistent with a radius of 1–2 m, as derived from the fireball observations. Although a large preatmospheric size was proposed, one fragment (SM18) contains solar cosmic ray–produced short-lived radionuclides, such as ⁵⁶Co and ⁵¹Cr. This implies that this specimen was less than 2 cm from the preatmospheric surface of Sutter’s Mill. Although this conclusion seems surprising, it is consistent with the observation that the meteoroid fragmented high in the atmosphere. The presence of SCR-produced nuclides is consistent with the high SCR fluxes observed during the last few months before the meteorite’s fall, when its orbit was less than 1 AU from the Sun.

Reference
Nishiizumi K, Caffee MW, Hamajima Y, Reedy RC and Welten KC (in press) Exposure history of the Sutter’s Mill carbonaceous chondrite. Meteoritics & Planetary Science
[doi:10.1111/maps.12297]
Published by arrangement with John Wiley & Sons

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Natalia S. Bezaeva¹ et al. (>10)*
*Find the extensive, full author and affiliation list on the publishers website.

¹Earth Physics Department, Faculty of Physics, M.V. Lomonosov Moscow State University, Moscow, Russia

Here we characterize the magnetic properties of the Chelyabinsk chondrite (LL5, S4, W0) and constrain the composition, concentration, grain size distribution, and mineral fabric of the meteorite’s magnetic mineral assemblage. Data were collected from 10 to 1073 K and include measurements of low-field magnetic susceptibility (χ₀), the anisotropy of χ₀, hysteresis loops, first-order reversal curves, Mössbauer spectroscopy, and X-ray microtomography. The REM and REM′ paleointensity protocols suggest that the only magnetizations recorded by the chondrite are components of the Earth’s magnetic field acquired during entry into our planet’s atmosphere. The Chelyabinsk chondrite consists of light and dark lithologies. Fragments of the light lithology show logχ₀ = 4.57 ± 0.09 (s.d.) (n = 135), while the dark lithology shows 4.65 ± 0.09 (n = 39) (where χ₀ is in 10⁻⁹ m³ kg⁻¹). Thus, Chelyabinsk is three times more magnetic than the average LL5 fall, but is similar to a subgroup of metal-rich LL5 chondrites (Paragould, Aldsworth, Bawku, Richmond) and L/LL5 chondrites (Glanerbrug, Knyahinya). The meteorite’s room-temperature magnetization is dominated by multidomain FeNi alloys taenite and kamacite (no tetrataenite is present). However, below approximately 75 K remanence is dominated by chromite. The metal contents of the light and dark lithologies are 3.7 and 4.1 wt%, respectively, and are based on values of saturation magnetization.

Reference
Bezaeva et al. (in press) Magnetic properties of the LL5 ordinary chondrite Chelyabinsk (fall of February 15, 2013). Meteoritics & Planetary Science
[doi:10.1111/maps.12307]
Published by arrangement with John Wiley & Sons

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