¹Geoffrey W. Marcy, ¹Lauren M. Weiss, ¹Erik A. Petigura, ¹Howard Isaacson, ²Andrew W. Howard,³Lars A. Buchhave
¹Department of Astronomy, University of California, Berkeley, CA 94720;
²Institute for Astronomy, University of Hawaii at Manoa, Honolulu, HI 96822; and
³Harvard-Smithsonian Center for Astrophysics, Harvard University, Cambridge, MA 02138

Small planets, 1–4× the size of Earth, are extremely common around Sun-like stars, and surprisingly so, as they are missing in our solar system. Recent detections have yielded enough information about this class of exoplanets to begin characterizing their occurrence rates, orbits, masses, densities, and internal structures. The Kepler mission finds the smallest planets to be most common, as 26% of Sun-like stars have small, 1–2 R⊕ planets with orbital periods under 100 d, and 11% have 1–2 R⊕ planets that receive 1–4× the incident stellar flux that warms our Earth. These Earth-size planets are sprinkled uniformly with orbital distance (logarithmically) out to 0.4 the Earth–Sun distance, and probably beyond. Mass measurements for 33 transiting planets of 1–4 R⊕ show that the smallest of them, R < 1.5 R⊕, have the density expected for rocky planets. Their densities increase with increasing radius, likely caused by gravitational compression. Including solar system planets yields a relation: ρ=2.32+3.19R/R ⊕  [g cm −3 ] . Larger planets, in the radius range 1.5–4.0 R⊕, have densities that decline with increasing radius, revealing increasing amounts of low-density material (H and He or ices) in an envelope surrounding a rocky core, befitting the appellation ‘‘mini-Neptunes.’’ The gas giant planets occur preferentially around stars that are rich in heavy elements, while rocky planets occur around stars having a range of heavy element abundances. Defining habitable zones remains difficult, without benefit of either detections of life elsewhere or an understanding of life’s biochemical origins.

Reference
Marcy GW, Lauren M. Weiss, Petigura EA, Isaacson H, Howard AW, Buchhave LA (2014) Occurrence and core-envelope structure of 1–4× Earth-size planets around Sun-like stars. Proceedings of the National Academy of Sciences 111, 35, 12655–12660
Link to Article [doi: 10.1073/pnas.1304197111]

Since the editors of this blog will spend the next week on various conferences, there will be only limited posting over the next ten days. Normal service will commence after that.

¹F. Goesmann et al. (>10)*
¹Max Planck Institute for Solar System Research, Göttingen, Germany
*Find the extensive, full author and affiliation list on the publishers website

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

Reference
Goesmann et al. (2014) COSAC prepares for sampling and in situ analysis of cometary matter from comet 67P/Churyumov-Gerasimenko. Planetary and Space Science (in Press)
Link to Article [DOI: 10.1016/j.pss.2014.08.006]

¹Addi Bischoff, ¹Marian Horstmann, ²Jean-Alix Barrat,
³Marc Chaussidon, ⁴Andreas Pack, ^4,5Daniel Herwartz, ¹Dustin Ward, ¹Christian Vollmer, ⁶Stephan Decker

¹Institut für Planetologie and Institut für Mineralogie, Westfälische Wilhelms-Universität Münster, 48149 Münster, Germany
²Institut Universitaire Européen de la Mer, Université de Bretagne Occidentale, 29280 Plouzané, France
³Institut de Physique du Globe, 75235 Paris, France
⁴Geowissenschaftliches Zentrum, Universität Göttingen, 37077 Göttingen, Germany
⁵Institut für Geologie und Mineralogie, Universität zu Köln, 50674 Köln, Germany
⁶Meteorite Museum, 55430 Oberwesel, Germany

Volcanism is a substantial process during crustal growth on planetary bodies and well documented to have occurred in the early Solar System from the recognition of numerous basaltic meteorites. Considering the ureilite parent body (UPB), the compositions of magmas that formed a potential UPB crust and were complementary to the ultramafic ureilite mantle rocks are poorly constrained. Among the Almahata Sitta meteorites, a unique trachyandesite lava (with an oxygen isotope composition identical to that of common ureilites) documents the presence of volatile- and SiO2-rich magmas on the UPB. The magma was extracted at low degrees of disequilibrium partial melting of the UPB mantle. This trachyandesite extends the range of known ancient volcanic, crust-forming rocks and documents that volcanic rocks, similar in composition to trachyandesites on Earth, also formed on small planetary bodies ∼4.56 billion years ago. It also extends the volcanic activity on the UPB by ∼1 million years (Ma) and thus constrains the time of disruption of the body to later than 6.5 Ma after the formation of Ca–Al-rich inclusions.

Reference
Bischoff A, Horstmann M, Barrat J-A, Chaussidon M, Pack A, Herwartz D, Ward D, Vollmer C, Decker S (2014) Trachyandesitic volcanism in the early Solar System. Proceedings of the National Academy of Sciences 111, 35, 12689–12692
Link to Article [doi: 10.1073/pnas.1404799111]

¹François S. Paquay, ¹Greg Ravizza, ²Rodolfo Coccioni
¹Dept. of Geology and Geophysics, University of Hawaii at Manoa, 1680 East West Road POST 712 Honolulu, HI 96822 USA
²Dipartimento di Scienze della Terra, della Vita e dell’Ambiente dell’Universita, Campus Scientifico, Località Crocicchia, 61209 Urbino,

A reconstruction of seawater 187Os/188Os ratios during the late Eocene (∼36-34 Ma), based upon bulk sediment analyses from the sub-Antarctic Southern Atlantic Ocean (Ocean Drilling Program (ODP) Site 1090), Eastern Equatorial Pacific Ocean (ODP Sites 1218 and 1219) and the uplifted (land-based) Tethyan section (Massignano, Italy), confirms that the previously reported abrupt shift to lower 187Os/188Os is a unique global feature of the marine Os isotope record that occurs in magnetochron C16n.1n. This feature is interpreted to represent the change in seawater 187Os/188Os caused by the Popigai impact event. Higher in the Massignano section, two other iridium anomalies previously proposed to represent additional impact events do not show a comparable excursion to low 187Os/188Os, suggesting that these horizons do not record multiple large impacts. Comparison of records from three different ocean basins indicates that seawater 187Os/188Os begins to decline in advance of the Popigai impact event. At Massignano this decline coincides with a previously reported episode of elevated 3He flux, suggesting that increased influx of interplanetary dust particles (IDPs) contributed to the pre-impact shift in 187Os/188Os and not to the longer-term latest Eocene 187Os/188Os decline that occurred ∼1 million year after the Popigai impact event.

Reference
Paquay FS, Ravizza G, Coccioni R (2014) The influence of extraterrestrial material on the late Eocene marine Os isotope record. Geochimica et Cosmoschimica Acta (in Press)
Link to Article [DOI: 10.1016/j.gca.2014.08.024]

Copyright Elsevier

¹Yasuhito Sekine,²Hidenori Genda, ¹Yuta Muto, ¹Seiji Sugita, ³Toshihiko Kadono, ⁴Takafumi Matsui
¹Department of Complexity Science & Engineering, University of Tokyo, Kashiwanoha, Kashiwa, 277-8561 Japan
²Earth-Life Science Institute, Tokyo Institute of Technology, Ookayama, Meguro, 152-8550, Japan
³School of Medicine, University of Occupational and Environmental Health, Iseigaoka, Kitakyusyu, 807-8555, Japan
⁴Planetary Exploration Research Center, Chiba Institute of Technology, Tsudanuma, Narashino, 275-0016 Japan

Methanol (CH3OH) is one of the primordial volatiles contained within icy solids in the outer solar nebula. This paper investigates the impact chemistry of CH3OH ice through a series of impact experiments. We discuss its fate during the accretion and evolution stages of large icy bodies, and assess the possibility of intact delivery of cometary volatiles to the lunar surface. Our experimental results show that the peak shock pressures for initial and complete dissociation of CH3OH ice are approximately 9 and 28 GPa, respectively. We also found that CO is more abundant than CH4 in the gas-phase products of impact-induced CH3OH dissociation. Our results further show that primordial CH3OH within icy planetesimals could have survived low-velocity impacts during accretion of icy satellites and dwarf planets. These results suggest that CH3OH may have been a source of soluble reducing carbon and that it may have acted as antifreeze in liquid interior oceans of large icy bodies. In contrast, CH3OH acquired by accretion on icy satellites and Ceres would have been dissociated efficiently by subsequent impacts, perhaps during the heavy bombardment period, owing to the expected high impact velocities. For example, if Callisto originally contained CH3OH, cometary impacts during the late heavy bombardment period would have resulted in the formation of a substantial atmosphere (ca. ⩾10–4 bar) composed of CO, H2, and CH4. To account for the current CO levels in Titan’s atmosphere, the CH3OH content in its crust may have been much lower than that typical of comets. Our numerical simulations also indicate that intact delivery of cometary CH3OH to the lunar surface would not have occurred, which suggests that CH3OH found in a persistently-shadowed lunar region probably formed through low-temperature surface chemistry on regolith.

Reference
Sekine Y, Genda H, Muto Y, Sugita S, Kadono T, Matsui T (2014) Impact chemistry of methanol: Implications for volatile evolution on icy satellites and dwarf planets, and cometary delivery to the Moon. Icarus (in Press)
Link to Article [DOI: 10.1016/j.icarus.2014.08.034]

Copyright Elsevier

¹D. Schwander, ¹T. Berg, ¹G. Schönhense, ^1´,2U. Ott
¹Institut für Physik, Johannes Gutenberg-Universität, Staudingerweg 7, D-55128 Mainz, Germany
²University of West Hungary, Károlyi Gáspár tér 4, H-9700 Szombathely, Hungary

The condensation of material from a gas of solar composition has been extensively studied, but less so condensation in the environment of evolved stars, which has been mainly restricted to major compounds and some specific element groups such as the Rare Earth elements. Also of interest, however, are refractory metals like Mo, Ru, Os, W, Ir, and Pt, which may condense to form refractory metal nuggets (RMNs) like the ones that have been found in association with presolar graphite. We have performed calculations describing the condensation of these elements in the outflows of s-process enriched AGB stars as well as from gas enriched in r-process products. While in carbon-rich environments (C > O), the formation of carbides is expected to consume W, Mo, and V (Lodders & Fegley), the condensation sequence for the other refractory metals under these conditions does not significantly differ from the case of a cooling gas of solar composition. The composition in detail, however, is significantly different due to the completely different source composition. Condensation from an r-process enriched source differs less from the solar case. Elemental abundance ratios of the refractory metals can serve as a guide for finding candidate presolar grains among the RMNs in primitive meteorites—most of which have a solar system origin—for confirmation by isotopic analysis. We apply our calculations to the case of the four RMNs found by Croat et al., which may very well be presolar.

Reference
Schwander D, Berg T, Schönhense G, Ott U (2014) Condensation of Refractory Metals in Asymptotic Giant Branch and Other Stellar Environments. The Astrophysical Journal 793 (in Press)
Link to Article [doi:10.1088/0004-637X/793/1/20]

¹Junya Matsuno, ¹Akira Tsuchiyama, ¹Akira Miyake, ²Ryo Noguchi, ³Satoshi Ichikawa
¹Department of Geology and Mineralogy, Graduate School of Science, Kyoto University, Kitashirakawa-Oiwake, Sakyo-ku, Kyoto 606-8502, Japan
²Department of Earth and Space Science, Graduate School of Science, Osaka University, 1-1 Machikaneyama, Toyonaka, Osaka 560-0043, Japan
³Institute for Nano-science Design, Osaka University, 1-3 Machikaneyama, Toyonaka, Osaka 560-8531, Japan

Glass with embedded metal and sulfides (GEMS) are amorphous silicates included in anhydrous interplanetary dust particles (IDPs) and can provide information about material evolution in our early solar system. Several formation processes for GEMS have been proposed so far, but these theories are still being debated. To investigate a possible GEMS origin by reduction of interstellar silicates, we synthesized amorphous silicates with a mean GEMS composition and performed heating experiments in a reducing atmosphere. FeO-bearing amorphous silicates were heated at 923 K and 973 K for 3 hr, and at 1023 K for 1-48 hr at ambient pressure in a reducing atmosphere. Fe grains formed at the interface between the silicate and the reducing gas through a reduction. In contrast, TEM observations of natural GEMS show that metallic grains are uniformly embedded in amorphous silicates. Therefore, the present study suggests that metallic inclusions in GEMS could not form as reduction products and that other formation process such as condensation or irradiation are more likely.

Reference
Matsuno J, Tsuchiyama A, Miyake A, Noguchi R, Ichikawa S (2014) Reduction Experiment of FeO-bearing Amorphous Silicate: Application to Origin of Metallic Iron in Gems. The Astrophysical Journal 792 (in Press)
Link to Article [doi:10.1088/0004-637X/792/2/136]

^1,2Ulrich Ott
¹University of West Hungary, Faculty of Natural Sciences, Savaria Campus, H-9700 Szombathely, Hungary
²Max 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 (2014) Planetary and pre-solar noble gases in meteorites. Chemie der Erde (in Press)
Link to Articel [DOI: 10.1016/j.chemer.2014.01.003]

Copyright Elsevier