Abstract-The Novato L6 chondrite fragmental breccia fell in California on 17 October 2012, and was recovered after the Cameras for Allsky Meteor Surveillance (CAMS) project determined the meteor's trajectory between 95 and 46 km altitude. The final fragmentation from 42 to 22 km altitude was exceptionally well documented by digital photographs. The first sample was recovered before rain hit the area. First results from a consortium study of the meteorite's characterization, cosmogenic and radiogenic nuclides, origin, and conditions of the fall are presented. Some meteorites did not retain fusion crust and show evidence of spallation. Before entry, the meteoroid was 35 AE 5 cm in diameter (mass 80 AE 35 kg) with a cosmic-ray exposure age of 9 AE 1 Ma, if it had a one-stage exposure history. A two-stage exposure history is more likely, with lower shielding in the last few Ma. Thermoluminescence data suggest a collision event within the last $ 0.1 Ma. Novato probably belonged to the class of shocked L chondrites that have a common shock age of 470 Ma, based on the U,Th-He age of 420 AE 220 Ma. The measured orbits of Novato, Jesenice, and Innisfree are consistent with a proposed origin of these shocked L chondrites in the Gefion asteroid family, perhaps directly via the 5:2 mean-motion resonance with Jupiter. Novato experienced a stronger compaction than did other L6 chondrites of shockstage S4. Despite this, a freshly broken surface shows a wide range of organic compounds.

By using chemo-dynamical simulations of the Milky Way-type galaxies formation, we find that the two α-sequences are formed in quite different physical environments. The high-α sequence is formed early from a burst of star formation in a turbulent, compact gaseous disc that forms a thick disc. The low-α stellar population is the result of quiescent star formation supported by the slow accretion of enriched gas on to a radially extended thin disc. Feedback-driven outflows during the formation of the thick disc are responsible for the enrichment of the surrounding gaseous halo, which subsequently feeds the disc on a longer time-scale. During the thin disc phase, chemical evolution reaches an equilibrium metallicity and abundance, where the stars pile-up. This equilibrium metallicity decreases towards the outer disc, generating the ridge line that forms the low-α sequence. We identify a second mechanism capable of creating a low-α sequence in one of our simulations. A rapid shutdown of the star formation due to feedback at the end of the thick disc phase, suppresses the chemical enrichment of the halo gas, which, once accreted on to the star-forming disc, dilutes the interstellar medium at the beginning of the thin disc formation. Therefore, the bimodality is independent of any particular merger history, suggesting that it could be much more widespread than has been claimed. We also find that radial migration has a negligible effect on the $\rm [\alpha / Fe]\!-\![Fe / H]$ distribution over time, suggesting that α-bimodality results purely from the presence of different star formation regimes over the galaxy’s formation.

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