A short timescale for changing oxygen fugacity in the solar nebula revealed by high-resolution 26Al26Mg dating of CAI rims

Abstract Most rocky objects in the solar system, including the primitive chondrites and the terrestrial planets themselves, formed at oxygen fugacities ( f O2 ) near that of the Iron-Wü stite (IW) f O2 buffer. Conversely, the most ancient rocky objects of the solar system, the calcium aluminum-rich inclusions (CAIs), formed at f O2 values 5 orders of magnitude lower than the IW buffer in an environment more closely resembling a solar gas. High-resolution Mg isotope data and estimates for f O2 for rims on CAIs show that this shift from~solar to protoplanetary (chondritic) f O2 occurred in 100,000 to 300,000 yr for these objects. Magnesium isotopes show further that the rise in f O2 was accompanied by a rise in the partial pressure of Mg. These results establish that CAIs entered a region resembling where planet progenitors formed within 3 Â 10 5 yr of their formation in the solar nebula.

Earliest rock fabric formed in the Solar System preserved in a chondrule rim

Rock fabrics – the preferred orientation of grains – provide a window into the history of rock formation, deformation and compaction. Chondritic meteorites are among the oldest materials in the Solar System1 and their fabrics should record a range of processes occurring in the nebula and in asteroids, but due to abundant fine-grained material these samples have largely resisted traditional in situ fabric analysis. Here we use high resolution electron backscatter diffraction to map the orientation of sub-micrometre grains in the Allende CV carbonaceous chondrite: the matrix material that is interstitial to the mm-sized spherical chondrules that give chondrites their name, and fine-grained rims which surround those chondrules. Although Allende matrix exhibits a bulk uniaxial fabric relating to a significant compressive event in the parent asteroid, we find that fine-grained rims preserve a spherically symmetric fabric centred on the chondrule. We define a method that quantitatively relates fabric intensity to net compression, and reconstruct an initial porosity for the rims of 70-80% - a value very close to model estimates for the earliest uncompacted aggregates2,3. We conclude that the chondrule rim textures formed in a nebula setting and may therefore be the first rock fabric to have formed in the Solar System

Millimeter wavelength measurements of the rotational spectrum of 2-aminoethanol

Aminoethanol is a predicted precursor to the amino acid alanine in the interstellar medium and is therefore of great interest for observational studies. However, previous work involving the rotational spectrum of this molecule is limited to centimeter wavelengths and additional laboratory work is necessary to support astronomical heterodyne spectroscopy. This work presents the Doppler-limited rotational spectrum of aminoethanol measured in selected regions between 72 and 305 GHz. Measurements of ground state and ν_(27) transitions have been extended up to J=51 and J=43, respectively. Additional rotational transitions were assigned for the ν_(25), ν_(26), ν_(25)+ν_(27), 2ν_(27) and ν_(26)+ν_(27) hot bands, resulting in improved rotational and centrifugal distortion constants for these states

Characterization Of Mason Gully (H5): The Second Recovered Fall From The Desert Fireball Network

Mason Gully, the second meteorite recovered using the Desert Fireball Network (DFN), is characterized using petrography, mineralogy, oxygen isotopes, bulk chemistry, and physical properties. Geochemical data are consistent with its classification as an H5 ordinary chondrite. Several properties distinguish it from most other H chondrites. Its 10.7% porosity is predominantly macroscopic, present as intergranular void spaces rather than microscopic cracks. Modal mineralogy (determined via PS-XRD, element mapping via energy dispersive spectroscopy [EDS], and X-ray tomography [for sulfide, metal, and porosity volume fractions]) consistently gives an unusually low olivine/orthopyroxene ratio (0.67-0.76 for Mason Gully versus ~1.3 for typical H5 ordinary chondrites). Widespread silicate darkening is observed. In addition, it contains a bright green crystalline object at the surface of the recovered stone (diameter ≈ 1.5 mm), which has a tridymite core with minor α-quartz and a rim of both low- and high-Ca pyroxene. The mineralogy allows the calculation of the temperatures and f(O2) characterizing thermal metamorphism on the parent body using both the two-pyroxene and the olivine-chromite geo-oxybarometers. These indicate that MG experienced a peak metamorphic temperature of ~900 °C and had a similar f(O2) to Kernouvé (H6) that was buffered by the reaction between olivine, metal, and pyroxene. There is no evidence for shock, consistent with the observed porosity structure. Thus, while Mason Gully has some unique properties, its geochemistry indicates a similar thermal evolution to other H chondrites. The presence of tridymite, while rare, is seen in other OCs and likely exogenous; however, the green object itself may result from metamorphism

Compositional Effects of Low-Pressure Impacts in Chondritic Meteorites: Oxygen Isotope Homogenization and Mg-Fe Diffusion in Matrix Olivine and Presolar Grains

Recent work has explored the effects of low-intensity impacts into porous chondrite precursors. We show oxygen-isotope homogenization of presolar grains and Mg-Fe diffusion in fine-grained matrix are potential consequences of this process

Towards a Digital Desert Fireball Network for Meteorite Recovery

We describe digital enhancements to the Desert Fireball Network, and detail the modelling and analysis work concerning the predicted fall rate over this next phase of the project

Constraining the Compositional Variety of Impactors at 1 AU Over the last ˜3.5 Ga: In Situ Identification and Analysis of >200 Meteoritic Grains in Lunar Soil

No abstract available

Constraining the Compositional Variety of Impactors at 1 AU Over the last ˜3.5 Ga: In Situ Identification and Analysis of >200 Meteoritic Grains in Lunar Soil

No abstract available

Effect of Low Intensity Impacts on Chondrite Matrix

Although the majority of carbonaceous chondrites have only experienced low-intensity (<5 GPa) impacts, we show that compacting initially highly porous matrix aggregates results in large temperature excursions even at low shock pressures