¹D. S. Burnett,^2,3A. J. G. Jurewicz, ⁴D. S. Woolum
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13266]
¹Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California, 91125 USA
²Center for Meteorite Studies/School of Earth and Space Exploration, Arizona State University, Tempe, Arizona, 85287–1404 USA
³Department of Earth Sciences, Dartmouth College, Hanover, New Hampshire, 03755, USA
⁴Department of Physics, California State University, Fullerton, California, 92831 USA
Published by arrangement with John Wiley & Sons

Solar abundances are important to planetary science since the prevalent model assumes that the composition of the solar photosphere is that of the solar nebula from which planetary materials formed. Thus, solar abundances are a baseline for planetary science. Previously, solar abundances have only been available through spectroscopy or by proxy (CI). The Genesis spacecraft collected and returned samples of the solar wind for laboratory analyses. Elemental and isotopic abundances in solar wind from Genesis samples have been successfully measured despite the crash of the re‐entry capsule. Here we present science rationales for a set of 12 important (and feasible postcrash) Science and Measurement Objectives as goals for the future (Table 1). We also review progress in Genesis sample analyses since the last major review (Burnett 2013). Considerable progress has been made toward understanding elemental fractionation during the extraction of the solar wind from the photosphere, a necessary step in determining true solar abundances from solar wind composition. The suitability of Genesis collectors for specific analyses is also assessed. Thus far, the prevalent model remains viable despite large isotopic variations in a number of volatile elements, but its validity and limitations can be further checked by several Objectives.

¹A.Pantazidi,¹I.Baziotis,^2,3A.Solomonidou,⁴E.Manoutsoglou,⁵D.Palles,⁵ E.Kamitsos,⁶A.Karageorgis,⁷G.Profitiliotis,¹M.Kondoyanni,⁸S.Klemme,⁸J.Berndt,⁹D.Ming,¹⁰P.Asimow
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2019.02.026]
¹Agricultural University of Athens, Mineral Resources and Agricultural Engineering, Iera Odos str. 75, 11855 Athens, Greece
²European Space Agency (ESA), European Space Astronomy Centre (ESAC), Madrid, Spain
³LESIA-Observatoire de Paris, Paris Sciences and Letters Research University, CNRS, Sorbonne Université, Université Paris-Diderot, Meudon, France
⁴Technical University of Crete, Greece
⁵National Hellenic Research Foundation, Athens, Greece
⁶Hellenic Centre for Marine Research (HCMR), Institute of Oceanography, Athens, Greece
⁷National Technical University of Athens, Greece
⁸Westfälische Wilhelms-Univ. Münster, Institut für Mineralogie, Correnstrasse 24, Münster, Germany
⁹NASA Johnson Space Center, Houston, TX 77058, USA
¹⁰California Institute of Technology, Geological and Planetary Sciences, Pasadena, CA, USA
Copyright Elsevier

The interpretation of geologic processes on Mars from sparse meteorite, remote sensing and rover data is influenced by knowledge gained from well-characterized terrestrial analogues. This calls for detailed study of candidate terrestrial analogues and comparison of their observable features to those encountered on the surface of Mars. We evaluated the mineralogical, geochemical, and physical properties of the Balos cove basalts (BCB) from the island of Santorini and compared them to Martian meteorites, Mars rover surface measurements, and other verified Martian analogues obtained from the International Space Analogue Rockstore (ISAR). Twenty rock samples were collected from the Balos cove area based on their freshness, integrity, and basaltic appearance in the field. Optical microscopy of BCB revealed a pilotaxitic to trachytic texture, with olivine and clinopyroxene phenocrysts in a fine groundmass of olivine, clinopyroxene, plagioclase, magnetite, and devitrified glass. All major minerals show normal zoning, including calcic plagioclase (An_78–85 at the core and An_60–76 at the rim), augite (En_36-48Wo_41-44Fs_11–21), and olivine (Fo_74–88). The dominant bands in the infrared-attenuated total reflectance (IR-ATR) spectra from BCB can be assigned to olivine (~875 cm⁻¹), calcic plagioclase (~1130 cm⁻¹), and augite (~970 cm⁻¹). The whole-rock chemical compositions and mineralogy of the BCB are similar to published analyses of typical olivine-phyric shergottites and basalts and basaltic materials analyzed in Gusev and Gale craters on Mars. BCB porosity is in the range of 7–15% and is similar to the porosities of the ISAR samples. Although no terrestrial rock is ever a perfect match to Martian compositions, the differences in mineralogy and geochemistry between BCB and some classes of Martian samples are relatively subtle and the basalts of Santorini are as close a match as other accepted Mars basalt analogues. The Santorini site offers excellent field logistics that, together with the petrology of the outcrop, makes it a valuable locality for testing and calibration deployments, field training, and other activities related to current and future Mars exploration.

¹Connor D.Hilton,¹Katherine R.Bermingham,¹Richard J.Walker,²J.McCoy
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2019.02.035]
¹Department of Geology, University of Maryland, College Park, Maryland, 20742, USA
²Department of Mineral Sciences, National Museum of Natural History, Smithsonian Institution, Washington, DC, 20560-0119, USA
Copyright Elsevier

The nucleosynthetic Mo, Ru, and W isotopic compositions of the South Byron Trio iron meteorite grouplet (SBT) are consistent with all three meteorites originating on a single parent body that formed in the carbonaceous chondrite (CC) isotopic domain within the Solar nebula. Consistent with a common origin, the highly siderophile element (HSE) concentrations of the SBT can be related to one another by moderate degrees of fractional crystallization of a parental melt with initially chondritic relative abundances of HSE, and with initial S and P contents of ∼7 and ∼1 wt. %, respectively. Tungsten-182 isotopic data for the SBT indicate the parent body underwent metal-silicate differentiation 2.1 ± 0.8 Myr after calcium aluminum rich inclusion formation, and thermal modeling suggests the parent body formed 1.1 ± 0.5 Myr after CAI formation. This accretion age is not resolved from the accretion ages of other CC and most noncarbonaceous (NC) type iron meteorite parent bodies. Comparison of the projected parental melt composition of the SBT to those projected for the IVA and IVB iron meteorite groups suggests that at least some portions of the CC nebular domain were more oxidized compared to the NC domain. In addition, comparison of the SBT parental melt S content to estimates for parent bodies of the IIAB, IIIAB, IVA, IID, and IVB “magmatic” iron meteorite groups suggests that CC type iron meteorite parental melts were characterized by a general depletion in S, in addition to depletions in some other moderately volatile elements.

Based on chemical and O isotope similarities, prior studies have suggested the possibility of a common parent body for the SBT and the Milton pallasite. Molybdenum and Ru isotopic compositions of Milton also provide permissive evidence for this. The HSE concentrations in the Milton metal, however, cannot be related to the SBT by any known crystal-liquid fractionation or mixing path. Thus, Milton more likely formed on a different, chemically distinct, but genetically identical parent body present in the CC nebular domain.

^1,2James M.D.Day,²Paolo A.Sossi,³Charles K.Shearer,^2,4Frederic Moynier
Geochimica et Cosmochimcia Acta(in Press) Link to Article [https://doi.org/10.1016/j.gca.2019.02.036]
¹Scripps Institution of Oceanography, University of California San Diego, La Jolla, CA 92093-0244, USA
²Institut de Physique du Globe de Paris, Université Paris Diderot, Sorbonne Paris Cité, 1 rue Jussieu, 75005, Paris, France
³Institute of Meteoritics, University of New Mexico, Albuquerque, NM 87131, USA
⁴Institut Universitaire de France, 75005, Paris
Copyright Elsevier

The Apollo 16 ‘Rusty Rock’ impact melt breccia 66095 is a volatile-rich sample, with the volatiles inherited through vapor condensation from an internal lunar source formed during thermo-magmatic evolution of the Moon. We report Cu and Fe isotope data for 66095 and find that bulk-rocks, residues and acid leaches span a relatively limited range of compositions (3.0 ±1.3 wt.% FeO [range = 2.0-4.8 wt.%], 5.4 ±3.1 ppm Cu [range = 3-12 ppm], average δ⁵⁶Fe of 0.15 ± 0.05‰ [weighted mean = 0.16‰] and δ⁶⁵Cu of 0.72 ± 0.14‰ [weighted mean = 0.78‰]). In contrast to the extreme enrichment of light isotopes of Zn and heavy isotopes of Cl in 66095, δ⁶⁵Cu and δ⁵⁶Fe in the sample lie within the previously reported range for lunar mare basalts (0.92 ± 0.16‰ and 0.12 ± 0.02‰, respectively). The lack of extreme isotopic fractionation for Cu and Fe isotopes reflects compositions inherent to 66095, with condensation of a cooling gas from impact-generated fumarolic activity at temperatures too low to lead to the condensation of Cu and Fe, but higher than required to condense Zn. Together with thermodynamic models, these constraints suggest that the gas condensed within 66095 between 700 and 900 °C (assuming a pressure of 10^-6 and an fO₂ of IW-2). That the Cu and Fe isotopic compositions of sample 66095 are within the range of mare basalts removes the need for an exotic, volatile-enriched source. The enrichment in Tl, Br, Cd, Sn, Zn, Pb, Rb, Cs, Ga, B, Cl, Li relative to Bi, Se, Te, Ge, Cu, Ag, Sb, Mn, P, Cr and Fe in the ‘Rusty Rock’ is consistent with volcanic outgassing models and indicates that 66095 likely formed distal from the original source of the gas. The volatile-rich character of 66095 is consistent with impact-generated fumarolic activity in the region of the Cayley Plains, demonstrating that volatile-rich rocks can occur on the lunar surface from outgassing of a volatile-poor lunar interior. The ‘Rusty Rock’ indicates that the lunar interior is significantly depleted in volatile elements and compounds and that volatile-rich lunar surface rocks likely formed through vapor condensation. Remote sensing studies have detected volatiles on the lunar surface, attributing them dominantly to solar wind. Based on the ‘Rusty Rock’, some of these surface volatiles may also originate from the Moon’s interior.

^1,2Chuantong Zhangab,^1,2Bingkui Miao,³Huaiyu He
Planetary and Space Science (in Press) Link to Article [https://doi.org/10.1016/j.pss.2019.02.007]
¹Institution of Meteorites and Planetary Materials Research, Guilin University of Technology, Guilin, 541006, China
²Key Laboratory of Planetary Geological Evolution, Guilin University of Technology, Guilin, 541006, China
³Key Laboratory of Earth and Planetary Physics, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, 100029, China

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¹Katarzyna Łuszczek,¹Tadeusz A.Przylibski
Planetary and Space Science (in Press) Link to Article [https://doi.org/10.1016/j.pss.2019.02.005]
¹Wrocław University of Science and Technology, Faculty of Geoengineering, Mining and Geology, Wybrzeże S. Wyspiańskiego 27, 50-370, Wrocław, Poland

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

¹Reddy, Vishnu et al. (>10)
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2019.02.018]
¹Lunar and Planetary Laboratory, University of Arizona, 1629 E University Blvd, Tucson, AZ 85721, USA
Coypright Elsevier

Impacts due to near-Earth objects (NEOs) are responsible for causing some of the great mass extinctions on Earth. While nearly all NEOs of diameter > 1 km, capable of causing a global climatic disaster, have been discovered and have negligible chance of impacting in the near future, we are far from completion in our effort to detect and characterize smaller objects. In an effort to test our preparedness to respond to a potential NEO impact threat, we conducted a community-led global planetary defense exercise with support from the NASA Planetary Defense Coordination Office. The target of our exercise was 2012 TC4, the ~10 m diameter asteroid that made a close pass by the Earth on 2017 October 12 at a distance of about 50,000 km. The goal of the TC4 observing campaign was to recover, track, and characterize 2012 TC4 as a hypothetical impactor in order to exercise the global planetary defense system involving observations, modeling, prediction, and communication. We made three attempts with the Very Large Telescope (VLT) on 2017 July 27, 31 and on 2017 August 5 and recovered 2012 TC4 within its ephemeris uncertainty at 2.2 arcmin from the nominal prediction. At visual magnitude V = 27, the recovery of 2012 TC4 is the faintest NEA detection thus far. If an impact during the 2017 close approach had been possible based on the 2012 astrometric data, these recovery observations would have been sufficient to confirm or rule out the impact. The first automatic detection by a survey (Pan-STARRS1) was on September 25, which is the earliest that 2012 TC4 would have been discovered in survey mode, if it had not been discovered in 2012. We characterized 2012 TC4 using photometry, spectroscopy and radar techniques. Based on photometric observations, we determined a rotation period of 12.2 min with an amplitude of 0.9 magnitudes. An additional lower amplitude period was detected, indicating that 2012 TC4 was in a state of non-principle axis rotation. The combined visible and near-infrared spectrum puts it in the taxonomic X-class. Radar observations at 3.75 m resolution placed only one to two range pixels on the asteroid and barely resolved it; this suggests that 2012 TC4 is less than about 20 m on its long axis. We also estimated the average circular polarization, SC/OC, of 2012 TC4 to be 0.57, which is relatively high among NEOs observed by radar to date (averaging 0.34 ± 0.28). High circular polarization ratios can be caused by a variety of mechanisms such as near-surface roughness, curvature at scales comparable to that of the radar wavelength, and a high refractive index. We also performed a probabilistic impact risk assessment exercise for hypothetical impactors based on the 2012 TC4 observing campaign. This exercise was performed as part of ongoing efforts to advance effective impact risk models and assessment processes for planetary defense. The 2012 TC4 close approach provided a valuable opportunity to test the application of these methods using realistically evolving observational data to define the modeling inputs. To this end, risk assessments were calculated at several epochs before and during the close approach, incorporating new information about 2012 TC4 as it became available. Two size ranges were assessed—one smaller size range (H = 26.7) similar to the actual 2012 TC4, and one larger size range (H = 21.9) to produce a greater-damage scenario for risk assessment. Across the epochs, we found that only irons caused significant damage for smaller size. For the larger size case, however, hydrous stones caused the greatest damage, anhydrous stones caused the least damage, and irons caused moderate damage. We note that the extent of damage depends on composition in different size regimes and, after astrometry, size is the most important physical property to determine for an incoming object.

^1,2S.Schröder,¹K.Rammelkamp,¹D.S.Vogt,²O.Gasnault,^1,3H.-W.Hübers
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2019.02.017]
¹Deutsches Zentrum für Luft- und Raumfahrt (DLR), Institut für Optische Sensorsysteme, Berlin, Germany
²Institut de Recherche en Astrophysique et Planétologie (IRAP, Université de Toulouse, CNRS, CNES, UPS), Toulouse, France
³Humboldt-Universität zu Berlin, Institut für Physik, Be
Copyright Elsevier

For in-situ geochemical analysis of the surface of Mars, laser-induced breakdown spectroscopy (LIBS) is a very useful technique and the first extraterrestrial LIBS instrument ChemCam will soon be followed by others. Appropriate normalization of real mission data that is taken under varying experimental and environmental conditions from diverse geologic samples is an ongoing topic. One approach is the scaling to emission line intensities of carbon and oxygen from the CO2-dominated low-pressure martian atmosphere as an internal standard. Here, we performed several experiments to examine the emission of carbon and oxygen from a simulated martian atmosphere on simple, mostly mono-elemental samples, and to compare the emission characteristics of the elements of both origins. Differences in laser irradiance were found to have the biggest impact on sample emission lines scaled to C and O emission of the atmosphere. The temporal behavior shown in time-resolved LIBS measurements is dominated by the degree of ionization, but the ratio of the neutral emission from the sample to neutral emission from the atmosphere also varies over time. The effect of different grain sizes was minor in comparison to the high intrinsic variation in the LIBS data. Different samples were found to affect the absolute intensity of atmospheric C(I) more than O(I). Furthermore, the C(I) emission was found to be inseparably superimposed by iron if the latter was present in the target. The results indicate limitations of the general suitability of atmospheric carbon and oxygen emission for normalization purposes of martian LIBS data.

Peter Hoppe, Jan Leitner, and János Kodolányi
Astrophysical Journal 869, 47 Link to Article [DOI: 10.3847/1538-4357/aaec0a]
Max Planck Institute for Chemistry, Hahn-Meitner-Weg 1, D-55128 Mainz, Germany

We report high-resolution (<100 nm) Mg and Si isotope data of 12 presolar silicate grains (230–440 nm) from red giant and/or asymptotic giant branch stars that were previously identified based on their anomalous O-isotopic compositions (11 Group 1 grains and one Group 2 grain) in five primitive meteorites. The data were acquired by NanoSIMS ion imaging with the new Hyperion ion source that permits Mg and Si isotope measurements of presolar silicates with higher precision than was possible before. For a subset of five Group 1 (“category A”) grains, ²⁵Mg/²⁴Mg and ²⁹Si/²⁸Si ratios correlate with the inferred initial ¹⁸O/¹⁶O ratios of their parent stars, a measure of stellar metallicity. The Mg and Si isotope data of category A grains show positive correlations in the δ²⁵Mg–δ ²⁶Mg, δ ²⁹Si–δ ³⁰Si, and δ ²⁵Mg–δ ²⁹Si spaces. The correlations between O-, Mg, and Si-isotopic compositions are best explained by Galactic chemical evolution (GCE), with only minor imprints of nucleosynthetic and mixing processes in the grains’ parent stars. Six Group 1 silicate (“category B”) grains have close-to-normal Mg and Si isotopic compositions, possibly the result of isotope exchange in interstellar space or the meteorite parent bodies. For Si in category A grains, we find, with ~2σ significance, a slightly shallower slope in the δ ²⁹Si–δ ³⁰Si space for the GCE than inferred from presolar SiC mainstream grains. The 2σ upper limit on the slope for the linear trend in the δ ²⁵Mg–δ ²⁶Mg space of category A grains is slightly lower than the slope-1 predicted by GCE models around solar metallicity.

Feng Long (龙凤)^1,2 et al. (>10)
Astrophysical Journal 869, 17 Link to Article [DOI: 10.3847/1538-4357/aae8e1]
¹Kavli Institute for Astronomy and Astrophysics, Peking University, Beijing 100871, People’s Republic of China

Rings are the most frequently revealed substructure in Atacama Large Millimeter/submillimeter Array (ALMA) dust observations of protoplanetary disks, but their origin is still hotly debated. In this paper, we identify dust substructures in 12 disks and measure their properties to investigate how they form. This subsample of disks is selected from a high-resolution (~012) ALMA 1.33 mm survey of 32 disks in the Taurus star-forming region, which was designed to cover a wide range of brightness and to be unbiased to previously known substructures. While axisymmetric rings and gaps are common within our sample, spiral patterns and high-contrast azimuthal asymmetries are not detected. Fits of disk models to the visibilities lead to estimates of the location and shape of gaps and rings, the flux in each disk component, and the size of the disk. The dust substructures occur across a wide range of stellar mass and disk brightness. Disks with multiple rings tend to be more massive and more extended. The correlation between gap locations and widths, the intensity contrast between rings and gaps, and the separations of rings and gaps could all be explained if most gaps are opened by low-mass planets (super-Earths and Neptunes) in the condition of low disk turbulence (α = 10⁻⁴). The gap locations are not well correlated with the expected locations of CO and N₂ ice lines, so condensation fronts are unlikely to be a universal mechanism to create gaps and rings, though they may play a role in some cases.