N. G. RUDRASWAMI¹, Yves MARROCCHI², M. SHYAM PRASAD¹, D. FERNANDES¹,Johan VILLENEUVE², and S. TAYLOR³
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13281]
¹National Institute of Oceanography (Council of Scientific and Industrial Research), Dona Paula, Goa 403004, India
²CRPG, CNRS, Universite de Lorraine, UMR 7358, Vandoeuvre-les-Nancy F-54501, France
³Cold Regions Research and Engineering Laboratory, 72 Lyme Road, Hanover, New Hampshire 03755–1290, USA
Published by arrangement with John Wiley & Sons

We identified 66 chromite grains from 42 of ~5000 micrometeorites collected from Indian Ocean deep‐sea sediments and the South Pole water well. To determine the chromite grains precursors and their contribution to the micrometeorite flux, we combined quantitative electron microprobe analyses and oxygen isotopic analyses by high‐resolution secondary ion mass spectrometry. Micrometeorite chromite grains show variable O isotopic compositions with δ¹⁸O values ranging from −0.8 to 6.0‰, δ¹⁷O values from 0.3 to 3.6‰, and Δ¹⁷O values from −0.9 to 1.6‰, most of them being similar to those of chromites from ordinary chondrites. The oxygen isotopic compositions of olivine, considered as a proxy of chromite in chromite‐bearing micrometeorites where chromite is too small to be measured in ion microprobe have Δ¹⁷O values suggesting a principal relationship to ordinary chondrites with some having carbonaceous chondrite precursors. Furthermore, the chemical compositions of chromites in micrometeorites are close to those reported for ordinary chondrite chromites, but some contribution from carbonaceous chondrites cannot be ruled out. Consequently, carbonaceous chondrites cannot be a major contributor of chromite‐bearing micrometeorites. Based on their oxygen isotopic and elemental compositions, we thus conclude with no ambiguity that chromite‐bearing micrometeorites are largely related to fragments of ordinary chondrites with a small fraction from carbonaceous chondrites, unlike other micrometeorites deriving largely from carbonaceous chondrites.

Ozan UNSALAN1,2 et al. (>10)
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13258]
¹University of Istanbul, 34134 Vezneciler, Fatih Istanbul, Turkey
²Ege University, 35100, Bornova, Izmir, Turkey
Published by arrangement with John Wiley & Sons

The Sariçiçek howardite meteorite shower consisting of 343 documented stones occurred on September 2, 2015 in Turkey and is the first documented howardite fall. Cosmogenic isotopes show that Sariçiçek experienced a complex cosmic‐ray exposure history, exposed during ~12–14 Ma in a regolith near the surface of a parent asteroid, and that an ~1 m sized meteoroid was launched by an impact 22 ± 2 Ma ago to Earth (as did one‐third of all HED meteorites). SIMS dating of zircon and baddeleyite yielded 4550.4 ± 2.5 Ma and 4553 ± 8.8 Ma crystallization ages for the basaltic magma clasts. The apatite U‐Pb age of 4525 ± 17 Ma, K‐Ar age of ~3.9 Ga, and the U,Th‐He ages of 1.8 ± 0.7 and 2.6 ± 0.3 Ga are interpreted to represent thermal metamorphic and impact‐related resetting ages, respectively. Petrographic; geochemical; and O‐, Cr‐, and Ti‐isotopic studies confirm that Sariçiçek belongs to the normal clan of HED meteorites. Petrographic observations and analysis of organic material indicate a small portion of carbonaceous chondrite material in the Sariçiçek regolith and organic contamination of the meteorite after a few days on soil. Video observations of the fall show an atmospheric entry at 17.3 ± 0.8 km s⁻¹ from NW; fragmentations at 37, 33, 31, and 27 km altitude; and provide a pre‐atmospheric orbit that is the first dynamical link between the normal HED meteorite clan and the inner Main Belt. Spectral data indicate the similarity of Sariçiçek with the Vesta asteroid family (V‐class) spectra, a group of asteroids stretching to delivery resonances, which includes (4) Vesta. Dynamical modeling of meteoroid delivery to Earth shows that the complete disruption of a ~1 km sized Vesta family asteroid or a ~10 km sized impact crater on Vesta is required to provide sufficient meteoroids ≤4 m in size to account for the influx of meteorites from this HED clan. The 16.7 km diameter Antionia impact crater on Vesta was formed on terrain of the same age as given by the ⁴He retention age of Sariçiçek. Lunar scaling for crater production to crater counts of its ejecta blanket show it was formed ~22 Ma ago.

Quanzhi Ye (叶泉志)^1,2,3 and Mikael Granvik^4,5
Astrophysical Journal 873, 104 Link to Article [DOI: 10.3847/1538-4357/ab05ba ]
¹Division of Physics, Mathematics and Astronomy, California Institute of Technology, Pasadena, CA 91125, USA
²Infrared Processing and Analysis Center, California Institute of Technology, Pasadena, CA 91125, USA
³Department of Physics and Astronomy, The University of Western Ontario, London, Ontario N6A 3K7, Canada
⁴Division of Space Technology, Luleå University of Technology, Box 848, SE-98128 Kiruna, Sweden
⁵Department of Physics, P.O. Box 64, FI-00014 University of Helsinki, Finland

The under-abundance of asteroids on orbits with small perihelion distances suggests that thermally driven disruption may be an important process in the removal of rocky bodies in the solar system. Here we report our study of how the debris streams arise from possible thermally driven disruptions in the near-Sun region. We calculate that a small body with a diameter 0.5 km can produce a sufficient amount of material to allow the detection of the debris at the Earth as meteor showers, and that bodies at such sizes thermally disrupt every ~2 kyr. We also find that objects from the inner parts of the asteroid belt are more likely to become Sun-approachers than those from the outer parts. We simulate the formation and evolution of the debris streams produced from a set of synthetic disrupting asteroids drawn from Granvik et al.’s near-Earth object population model, and find that they evolve 10–70 times faster than streams produced at ordinary solar distances. We compare the simulation results to a catalog of known meteor showers on Sun-approaching orbits. We show that there is a clear overabundance of Sun-approaching meteor showers, which is best explained by a combining effect of comet contamination and an extended disintegration phase that lasts up to a few thousand years. We suggest that a few asteroid-like Sun-approaching objects that brighten significantly at their perihelion passages could, in fact, be disrupting asteroids. An extended period of thermal disruption may also explain the widespread detection of transiting debris in exoplanetary systems.

Ming-Ming Kang (康明铭)^1,2, Yang Hu (胡杨)³, Hong-Bo Hu (胡红波)^4,5, and Shou-Hua Zhu (朱守华)^6,7,8
Astrophysical Journal 873, 68 Link to Article [DOI: 10.3847/1538-4357/ab0178 ]
¹College of Physical Science and Technology, Sichuan University, Chengdu, Sichuan 610065, People’s Republic of China
²Key Laboratory of Radiation Physics and Technology of Ministry of Education, Sichuan University, Chengdu, Sichuan 610065, People’s Republic of China
³College of Arts and Sciences, Shanghai Maritime University, Shanghai 201306, People’s Republic of China
⁴Key Laboratory of Particle Astrophysics, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049, People’s Republic of China
⁵University of Chinese Academy of Sciences, Beijing 100049, People’s Republic of China
⁶Institute of Theoretical Physics & State Key Laboratory of Nuclear Physics and Technology, Peking University, Beijing 100871, People’s Republic of China
⁷Collaborative Innovation Center of Quantum Matter, Beijing 100871, People’s Republic of China
⁸Center for High Energy Physics, Peking University, Beijing 100871, People’s Republic of China

The discrepancy between the theoretical prediction of primordial lithium abundances and astronomical observations is called the Lithium Problem. We assume that during Big Bang Nucleosynthesis (BBN), nucleons can gain energy and deviate from thermal equilibrium, namely BBN cosmic rays (BBNCRs). BBNCR primary spectra are uncertain and the Coulomb energy-loss processes are neglected; however, we suppose a steady state of BBNCR spectra referring to the Galactic cosmic ray spectra observed today, to see constraints on BBNCRs, for example, the amount and energy range, not sticking to the explicit shape of the spectra. Such extra contributions from BBNCRs can explain the discrepancy, for both Li-7 and Li-6, and will change the deuterium abundance by only a little. The allowed parameter space of such an amount of nonthermal particles and the energy range are shown. The hypothesis is stable regardless of the cross-section uncertainty of relevant reactions and the explicit shape of the energy spectrum.