^1,2Mutsumi Komatsu, ²Timothy J. Fagan, ³Alexander N. Krot, ³Kazuhide Nagashima, ^4,5Michail I. Petaev, ^6,7Makoto Kimura, ^6,8Akira Yamaguchi
Proceedings of the National Academy of Sciences of the United States of America
Link to Article [https://doi.org/10.1073/pnas.1722265115]
¹The Graduate University for Advanced Studies (SOKENDAI), Hayama, 240-0193 Kanagawa, Japan
²Department of Earth Sciences, Waseda University, Shinjuku, 169-8050 Tokyo, Japan
³Hawai‘i Institute of Geophysics and Planetology, School of Ocean, Earth Science and Technology, University of Hawai‘i at Mānoa, Honolulu, HI 96822
⁴Department of Earth and Planetary Sciences, Harvard University, Cambridge, MA 02138
⁵Harvard–Smithsonian Center for Astrophysics, Cambridge, MA 02138
⁶National Institute of Polar Research, Tachikawa, 190-8518 Tokyo, Japan
⁷Ibaraki University, 310-8512 Mito, Japan
⁸Department of Polar Science, School of Multidisciplinary Science, SOKENDAI, Tachikawa, 190-8518 Tokyo, Japan

Calcium-aluminum–rich inclusions (CAIs) and amoeboid olivine aggregates (AOAs), a refractory component of chondritic meteorites, formed in a high-temperature region of the protoplanetary disk characterized by approximately solar chemical and oxygen isotopic (Δ¹⁷O ∼ −24‰) compositions, most likely near the protosun. Here we describe a ¹⁶O-rich (Δ¹⁷O ∼ −22 ± 2‰) AOA from the carbonaceous Renazzo-type (CR) chondrite Yamato-793261 containing both (i) an ultrarefractory CAI and (ii) forsterite, low-Ca pyroxene, and silica, indicating formation by gas–solid reactions over a wide temperature range from ∼1,800 to ∼1,150 K. This AOA provides direct evidence for gas–solid condensation of silica in a CAI/AOA-forming region. In a gas of solar composition, the Mg/Si ratio exceeds 1, and, therefore, silica is not predicted to condense under equilibrium conditions, suggesting that the AOA formed in a parcel of gas with fractionated Mg/Si ratio, most likely due to condensation of forsterite grains. Thermodynamic modeling suggests that silica formed by condensation of nebular gas depleted by ∼10× in H and He that cooled at 50 K/hour at total pressure of 10⁻⁴ bar. Condensation of silica from a hot, chemically fractionated gas could explain the origin of silica identified from infrared spectroscopy of remote protostellar disks.

¹Hadrien A.R. Devillepoix et al. (>10)
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13142]
¹School of Earth and Planetary Sciences, Curtin UniversityBentley, WA, Australia
Published by arrangement with John Wiley & Sons

We describe the fall of the Dingle Dell (L/LL 5) meteorite near Morawa in Western Australia on October 31, 2016. The fireball was observed by six observatories of the Desert Fireball Network (DFN), a continental‐scale facility optimized to recover meteorites and calculate their pre‐entry orbits. The 30 cm meteoroid entered at 15.44 km s−1, followed a moderately steep trajectory of 51° to the horizon from 81 km down to 19 km altitude, where the luminous flight ended at a speed of 3.2 km s−1. Deceleration data indicated one large fragment had made it to the ground. The four person search team recovered a 1.15 kg meteorite within 130 m of the predicted fall line, after 8 h of searching, 6 days after the fall. Dingle Dell is the fourth meteorite recovered by the DFN in Australia, but the first before any rain had contaminated the sample. By numerical integration over 1 Ma, we show that Dingle Dell was most likely ejected from the Main Belt by the 3:1 mean motion resonance with Jupiter, with only a marginal chance that it came from the ν6 resonance. This makes the connection of Dingle Dell to the Flora family (currently thought to be the origin of LL chondrites) unlikely.