Ulrich Ott

University of West Hungary, Faculty of Natural Sciences, Savaria Campus, H-9700 Szombathely, Hungary
Max Planck Institute for Chemistry, Hahn-Meitner-Weg 1, D-55128 Mainz, Germany

Noble gases are not rare in the Universe, but they are rare in rocks. As a consequence, it has been possible to identify in detailed analyses a variety of components whose existence is barely visible in other elements: radiogenic and cosmogenic gases produced in situ, as well as a variety of “trapped” components – both of solar (solar wind) origin and the “planetary” noble gases. The latter are most abundant in the most primitive chondritic meteorites and are distinct in elemental and isotopic abundance patterns from planetary noble gases sensu strictu, e.g., those in the atmospheres of Earth and Mars, having in common only the strong relative depletion of light relative to heavy elements when compared to the solar abundance pattern. In themselves, the “planetary” noble gases in meteorites constitute again a complex mixture of components including such hosted by pre-solar stardust grains.

The pre-solar components bear witness of the processes of nucleosynthesis in stars. In particular, krypton and xenon isotopes in pre-solar silicon carbide and graphite grains keep a record of physical conditions of the slow-neutron capture process (s-process) in asymptotic giant branch (AGB) stars. The more abundant Kr and Xe in the nanodiamonds, on the other hand, show a more enigmatic pattern, which, however, may be related to variants of the other two processes of heavy element nucleosynthesis, the rapid neutron capture process (r-process) and the p-process producing the proton-rich isotopes.
“Q-type” noble gases of probably “local” origin dominate the inventory of the heavy noble gases (Ar, Kr, Xe). They are hosted by “phase Q”, a still ill-characterized carbonaceous phase that is concentrated in the acid-insoluble residue left after digestion of the main meteorite minerals in HF and HCl acids. While negligible in planetary-gas-rich primitive meteorites, the fraction carried by “solubles” becomes more important in chondrites of higher petrologic type. While apparently isotopically similar to Q gas, the elemental abundances are somewhat less fractionated relative to the solar pattern, and they deserve further study. Similar “planetary” gases occur in high abundance in the ureilite achondrites, while small amounts of Q-type noble gases may be present in some other achondrites. A “subsolar” component, possibly a mixture of Q and solar noble gases, is found in enstatite chondrites. While no definite mechanism has been identified for the introduction of the planetary noble gases into their meteoritic host phases, there are strong indications that ion implantation has played a major role.
The planetary noble gases are concentrated in the meteorite matrix. Ca-Al-rich inclusions (CAIs) are largely planetary-gas-free, however, some trapped gases have been found in chondrules. Micrometeorites (MMs) and interplanetary dust particles (IDPs) often contain abundant solar wind He and Ne, but they are challenging objects for the analysis of the heavier noble gases that are characteristic for the planetary component. The few existing data for Xe point to a Q-like isotopic composition. Isotopically Q-Kr and Q-Xe show a mass dependent fractionation relative to solar wind, with small radiogenic/nuclear additions. They may be closer to “bulk solar” Kr and Xe than Kr and Xe in the solar wind, but for a firm conclusion it is necessary to gain a better understanding of mass fractionation during solar wind acceleration.

Reference
Ott U (in press) Planetary and pre-solar noble gases in meteorites. Chemie der Erde – Geochemistry
[doi:10.1016/j.chemer.2014.01.003]
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M. González, P. J. Gutiérrez and L. M. Lara

Instituto de Astrofísica de Andalucía, Glorieta de la Astronomía s/n 18008 Granada, Spain

Aims. In this work, we simulate the global behavior of comet Hale-Bopp with our thermophysical model starting with simple, homogeneous conditions, so that dust mantling and the active area develop consistently depending on the properties of the simulated nucleus. We aim to obtain a range of compatibility between our model and the observations, that can be used as constraints on some of the characteristics of cometary nuclei.
Methods. Our thermophysical model includes crystallization (and release of trapped CO), sublimation/recondensation, heat and gas transport through the nucleus, and dragged dust release. We run a battery of simulations with different parameter sets selected according to our current knowledge of comets and compare our results with observational data. Initial calculations are performed for a comet radius R₀ = 30 km. To match the calculated integrated H₂O production to the observed rate, we renormalize to a new R, which must be within 20 and 40 km, that is a range compatible with several estimates. Further selection is performed comparing the simulated water and carbon monoxide production rate profiles with the observational profiles and checking that the observational upper/lower limits of the H₂O production are fulfilled.
Results. We have found a reasonable agreement between our model and the data for H₂O and CO production rates, without the need of distributed sources, for the following initial conditions: the nucleus is composed of water, carbon monoxide, and dust with a moderate dust proportion, tending to be icy, with a dust-to-ice ratio of between 0.5 and 1. The water ice must be initially amorphous with 15 to 20% of trapped carbon monoxide. The icy matrix has a thermal inertia between 100 and 200 J m^-2 K s^−1/2, considering the initial composition with crystalline ice at 140 K. The dust follows an exponential size distribution with particles from 0.1 μm to 1 mm and leaves the comet dragged by the expelled vapor with a dragging efficiency (dust-to-gas ratio) of 3.

Reference
González M, Gutiérrez PJ and Lara LM (2014) Thermophysical simulations of comet Hale-Bopp. Astronomy & Astrophysics 563:A98.
[doi:10.1051/0004-6361/201322702]
Reproduced with permission © ESO

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Hainaut et al.¹ et al. (>10)*
*Find the extensive, full author and affiliation list on the publishers website.

¹ European Southern Observatory (ESO), Karl Schwarzschild Straße, 85 748 Garching bei München, Germany

The object P/2013 P5 PANSTARRS was discovered in August 2013, displaying a cometary tail, but its orbital elements indicated that it was a typical member of the inner asteroid main belt. We monitored the object from 2013 August 30 until 2013 October 05 using the CFHT 3.6 m telescope (Mauna Kea, HI), the NTT (ESO, La Silla), the CA 1.23 m telescope (Calar Alto), the Perkins 1.8m (Lowell) and the 0.6 m TRAPPIST telescope (La Silla). We measured its nuclear radius to be r ≲ 0.25−0.29 km, and its colours g′ − r′ = 0.58 ± 0.05 and r′ − i′ = 0.23 ± 0.06, typical for an S-class asteroid, as expected for an object in the inner asteroid belt and in the vicinity of the Flora collisional family. We failed to detect any rotational light curve with an amplitude <0.05 mag and a double-peaked rotation period <20 h. The evolution of the tail during the observations was as expected from a dust tail. A detailed Finson-Probstein analysis of deep images acquired with the NTT in early September and with the CFHT in late September indicated that the object was active since at least late January 2013 until the time of the latest observations in 2013 September, with at least two peaks of activity around 2013 June 14 ± 10 d and 2013 July 22 ± 3 d. The changes of activity level and the activity peaks were extremely sharp and short, shorter than the temporal resolution of our observations (~1 d). The dust distribution was similar during these two events, with dust grains covering at least the 1–1000 μm range. The total mass ejected in grains <1 mm was estimated to be 3.0 × 10⁶ kg and 2.6 × 10⁷ kg around the two activity peaks. Rotational disruption cannot be ruled out as the cause of the dust ejection. We also propose that the components of a contact binary might gently rub and produce the observed emission. Volatile sublimation might also explain what appears as cometary activity over a period of 8 months. However, while main belt comets best explained by ice sublimation are found in the outskirts of the main belt, where water ice is believed to be able to survive buried in moderately large objects for the age of the solar system deeply, the presence of volatiles in an object smaller than 300 m in radius would be very surprising in the inner asteroid belt.

Reference
Hainaut et al. (2014) Continued activity in P/2013 P5 PANSTARRS – Unexpected comet, rotational break-up, or rubbing binary asteroid?. Astronomy & Astrophysics 563:A75.
[doi:10.1051/0004-6361/201322864]
Reproduced with permission © ESO

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

^aJacobs, NASA Johnson Space Center, Mail Code JE-23, Building 31, Houston TX 77058

Carbonaceous matter on the surfaces of black pyroclastic beads, collected from Shorty crater during the Apollo 17 mission, represents the first identification of complex organic material associated with any lunar sample. We report the chemical, physical and isotopic properties of this organic matter that together support a pre-terrestrial origin. We suggest the most probable source is through the accretion of exogenous meteoritic kerogen from micrometeorite impacts into the lunar regolith. Abiotic organic matter has been continuously delivered to the surfaces of the terrestrial planets and their moons by accretion of asteroidal and cometary material. Determining the nature, distribution and evolution of such matter in the lunar regolith has important implications for understanding the prebiotic chemical inventory of the terrestrial planets.

Reference
Thomas-Keprta et al. (in press) Organic Matter on the Earth’s Moon. Geochimica et Cosmochimica Acta
[doi:10.1016/j.gca.2014.02.047]
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M. M. Woolfson

Physics Department, University of York, Heslington, York, YO10 5DD, UK

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

Reference
Woolfson MM (2013) A Postulated Planetary Collision, the Terrestrial Planets, the Moon and Smaller Solar-System Bodies. Earth, Moon, and Planets 111:1-14.
[doi:10.1007/s11038-013-9420-8]

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B. B. Ochsendorf¹, N. L. J. Cox², S. Krijt¹, F. Salgado¹, O. Berné⁴, J. P. Bernard⁴, L. Kaper³ and A. G. G. M. Tielens¹

¹Leiden Observatory, Leiden University, PO Box 9513 2300 RA Leiden The Netherlands
²Instituut voor Sterrenkunde, K.U. Leuven, Celestijnenlaan 200D, bus 2401, 3001 Leuven, Belgium
³Sterrenkundig Instituut Anton Pannekoek, University of Amsterdam, Science Park 904, PO Box 94249, 1090 GE Amsterdam, The Netherlands
⁴Université de Toulouse, UPS-OMP, IRAP, 31028 Toulouse, France

Observations obtained with the Spitzer Space Telescope and the WISE satellite have revealed a prominent arc-like structure at 50′′ (≃0.1 pc) from the O9.5V/B0.5V system σOri AB. We measure a total dust mass of 2.3 ± 1.5 × 10^-5  M_⊙. The derived dust-to-gas mass ratio is ≃0.29 ± 0.20. We attribute this dust structure to the interaction of radiation pressure from the star with dust carried along by the IC 434 photo-evaporative flow of ionized gas from the dark cloud L1630. We have developed a quantitative model for the interaction of a dusty ionized flow with nearby (massive) stars where radiation pressure stalls dust, piling it up at an appreciable distance (>0.1 pc), and force it to flow around the star. The model demonstrates that for the conditions in IC 434, the gas will decouple from the dust and will keep its original flow lines. Hence, we argue that this dust structure is the first example of a dust wave created by a massive star moving through the interstellar medium. Our model shows that for higher gas densities, coupling is more efficient and a bow wave will form, containing both dust and gas. Our model describes the physics of dust waves and bow waves and quantitatively reproduces the optical depth profile at 70 μm. Dust waves (and bow waves) stratify dust grains according to their radiation pressure opacity, which reflects the size distribution and composition of the grain material. It is found that in the particular case of σ Ori AB, dust is able to survive inside the ionized region. Comparison of our model results with observations implies that dust-gas coupling through Coulomb interaction is less important than previously thought, challenging our understanding of grain dynamics in hot, ionized regions of space. We describe the difference between dust (and bow) waves and classical bow shocks created by the interaction of a stellar wind with the interstellar medium. The results show that for late O-type stars with weak stellar winds, the stand-off distance of the resulting bow shock is very close to the star, well within the location of the dust wave. In general, we conclude that dust waves and bow waves should be common around stars showing the weak-wind phenomenon, i.e., stars with log(L/L_⊙)<5.2, and that these structures are best observed at mid-IR to FIR wavelengths, depending on the stellar spectral type. In particular, dust waves and bow waves are most efficiently formed around weak-wind stars moving through a high density medium. Moreover, they provide a unique opportunity to study the direct interaction between a (massive) star and its immediate surroundings.

Reference
Ochsendorf BB, Cox NLJ, Krijt S, Salgado F, Berné O, Bernard JP, Kaper L and Tielens AGGM (2014) Blowing in the wind: The dust wave around σ Orionis AB. Astronomy & Astrophysics 563:A65.
[doi:10.1051/0004-6361/201322873]
Reproduced with permission © ESO

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Catherine Walsh^1,2, Tom. J. Millar², Hideko Nomura^3,4,5, Eric Herbst^6,7, Susanna Widicus Weaver⁸, Yuri Aikawa⁹, Jacob C. Laas⁸ and Anton I. Vasyunin^10,11

¹Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands
²Astrophysics Research Centre, School of Mathematics and Physics, Queen’s University Belfast, University Road, Belfast BT7 1NN, UK
³Department of Astronomy, Graduate School of Science, Kyoto University, 606-8502 Kyoto, Japan
⁴National Astronomical Observatory of Japan, Osawa, Mitaka, Tokyo 181-8588, Japan
⁵Department of Earth and Planetary Sciences, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro-ku, 152-8551 Tokyo, Japan
⁶Departments of Physics, Chemistry and Astronomy, The Ohio State University, Columbus OH 43210, USA
⁷Departments of Chemistry, Astronomy, and Physics, University of Virginia, Charlottesville VA 22904, USA
⁸Department of Chemistry, Emory University, Atlanta GA 30322, USA
⁹Department of Earth and Planetary Sciences, Kobe University, 1-1 Rokkodai-cho, Nada, 657-8501 Kobe, Japan
¹⁰Department of Chemistry, University of Virginia, Charlottesville VA 22904, USA
¹¹Visiting Scientist, Ural Federal University, 620075 Ekaterinburg, Russia

Context. Protoplanetary disks are vital objects in star and planet formation, possessing all the material, gas and dust, which may form a planetary system orbiting the new star. Small, simple molecules have traditionally been detected in protoplanetary disks; however, in the ALMA era, we expect the molecular inventory of protoplanetary disks to significantly increase.
Aims. We investigate the synthesis of complex organic molecules (COMs) in protoplanetary disks to put constraints on the achievable chemical complexity and to predict species and transitions which may be observable with ALMA.
Methods. We have coupled a 2D steady-state physical model of a protoplanetary disk around a typical T Tauri star with a large gas-grain chemical network including COMs. We compare the resulting column densities with those derived from observations and perform ray-tracing calculations to predict line spectra. We compare the synthesised line intensities with current observations and determine those COMs which may be observable in nearby objects. We also compare the predicted grain-surface abundances with those derived from cometary comae observations.
Results. We find COMs are efficiently formed in the disk midplane via grain-surface chemical reactions, reaching peak grain-surface fractional abundances ~10^-6–10^-4 that of the H nuclei number density. COMs formed on grain surfaces are returned to the gas phase via non-thermal desorption; however, gas-phase species reach lower fractional abundances than their grain-surface equivalents, ~10^-12–10^-7. Including the irradiation of grain mantle material helps build further complexity in the ice through the replenishment of grain-surface radicals which take part in further grain-surface reactions. There is reasonable agreement with several line transitions of H₂CO observed towards T Tauri star-disk systems. There is poor agreement with HC₃N lines observed towards LkCa 15 and GO Tau and we discuss possible explanations for these discrepancies. The synthesised line intensities for CH₃OH are consistent with upper limits determined towards all sources. Our models suggest CH₃OH should be readily observable in nearby protoplanetary disks with ALMA; however, detection of more complex species may prove challenging, even with ALMA “Full Science” capabilities. Our grain-surface abundances are consistent with those derived from cometary comae observations providing additional evidence for the hypothesis that comets (and other planetesimals) formed via the coagulation of icy grains in the Sun’s natal disk.

Reference
Walsh C, Millar TJ, Nomura H, Herbst E, Weaver SW, Aikawa Y, Laas JC and Vasyunin AI (2014) Complex organic molecules in protoplanetary disks. Astronomy & Astrophysics 563:A33.
[doi:10.1051/0004-6361/201322446]
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Stephanie C. Werner¹, Anouck Ody², François Poulet³

¹The Centre for Earth Evolution and Dynamics, University of Oslo, Sem Sælandsvei 24, 0371 Oslo, Norway.
²Laboratoire de Géologie de Lyon: Terre, Planètes, Environnement, Université de Lyon 1 (CNRS, ENS-Lyon, Université de Lyon), rue Raphaël Dubois 2, 69622 Villeurbanne, France.
³Institut d’Astrophysique Spatiale, Université Paris Sud 11, Bâtiment 121, 91405 Orsay, France.

Absolute ages for planetary surfaces are often inferred by crater densities and only indirectly constrained by the ages of meteorites. We show that the <5 million-year-old and 55-km-wide Mojave Crater on Mars is the ejection source for the meteorites classified as shergottites. Shergottites and this crater are linked by their coinciding meteorite ejection ages and the crater formation age and by mineralogical constraints. Because Mojave formed on 4.3 billion–year-old terrain, the original crystallization ages of shergottites are old, as inferred by Pb-Pb isotope ratios, and the much-quoted shergottite ages of <600 million years are due to resetting. Thus, the cratering-based age determination method for Mars is now calibrated in situ, and it shifts the absolute age of the oldest terrains on Mars backward by 200 million years.

Reference
Werner SC, Ody A and Poulet F (2014) The Source Crater of Martian Shergottite Meteorites. Science 343:1343-1346.
[doi:10.1126/science.1247282]
Reprinted with permission from AAAS

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

^aInstitute of Planetary Research, German Aerospace Center (DLR), Berlin, Germany

The Quadrangles Av-11 and Av-12 on Vesta are located at the northern rim of the giant Rheasilvia south polar impact basin. The primary geologic units in Av-11 and Av-12 include material from the Rheasilvia impact basin formation, smooth material and different types of impact crater structures (such as bimodal craters, dark and bright crater ray material and dark ejecta material). Av-11 and Av-12 exhibit almost the full range of mass wasting features observed on Vesta, such as slump blocks, spur-and-gully morphologies and landslides within craters. Processes of collapse, slope instability and seismically triggered events force material to slump down crater walls or scarps and produce landslides or rotational slump blocks. The spur-and-gully morphology that is known to form on Mars is also observed on Vesta; however, on Vesta this morphology formed under dry conditions.

Reference
Krohn et al. (in press) Mass movement on Vesta at steep scarps and crater rims. Icarus
[doi:10.1016/j.icarus.2014.03.013]
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Blewett^a et al. (>10)*
*Find the extensive, full author and affiliation list on the publishers website.

^aPlanetary Exploration Group, Space Department, Johns Hopkins University Applied Physics Laboratory, MS 200-W230, 11100 Johns Hopkins Road, Laurel, Maryland 20723 USA

As part of systematic global mapping of Vesta using data returned by the Dawn spacecraft, we have produced a geologic map of the north pole quadrangle, Av-1 Albana. Extensive seasonal shadows were present in the north polar region at the time of the Dawn observations, limiting the ability to map morphological features and employ color or spectral data for determination of composition. The major recognizable units present include ancient cratered highlands and younger crater-related units (undivided ejecta, and mass-wasting material on crater floors). The antipode of Vesta’s large southern impact basins, Rheasilvia and Veneneia, lie within or near the Av-1 quadrangle. Therefore it is of particular interest to search for evidence of features of the kind that are found at basin antipodes on other planetary bodies. Albedo markings known as lunar swirls are correlated with basin antipodes and the presence of crustal magnetic anomalies on the Moon, but lighting conditions preclude recognition of such albedo features in images of the antipode of Vesta’s Rheasilvia basin. “Hilly and lineated terrain,” found at the antipodes of large basins on the Moon and Mercury, is not present at the Rheasilvia or Veneneia antipodes. We have identified small-scale linear depressions that may be related to increased fracturing in the Rheasilvia and Veneneia antipodal areas, consistent with impact-induced stresses (  and ). The general high elevation of much of the north polar region could, in part, be a result of uplift caused by the Rheasilvia basin-forming impact, as predicted by numerical modeling ( Bowling et al., 2013). However, stratigraphic and crater size-frequency distribution analysis indicate that the elevated terrain predates the two southern basins and hence is likely a remnant of the ancient vestan crust. The lack of large-scale morphological features at the basin antipodes can be attributed to weakened antipodal constructive interference of seismic waves caused by an oblique impact or by Vesta’s non-spherical shape, or by attenuation of seismic waves because of the physical properties of Vesta’s interior. A first-order analysis of the Dawn global digital elevation model for Vesta indicates that areas of permanent shadow are unlikely to be present in the vicinity of the north pole.

Reference
Blewett et al. (in press) Vesta’s North Pole Quadrangle Av-1 (Albana): Geologic Map and the Nature of the South Polar Basin Antipodes. Icarus
[doi:10.1016/j.icarus.2014.03.007]
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