A Global Fireball Observatory

The world's meteorite collections contain a very rich picture of what the early Solar System would have been made of, however the lack of spatial context with respect to their parent population for these samples is an issue. The asteroid population is equally as rich in surface mineralogies, and mapping these two populations (meteorites and asteroids) together is a major challenge for planetary science. Directly probing asteroids achieves this at a high cost. Observing meteorite falls and calculating their pre-atmospheric orbit on the other hand, is a cheaper way to approach the problem. The Global Fireball Observatory (GFO) collaboration was established in 2017 and brings together multiple institutions (from Australia, USA, Canada, Morocco, Saudi Arabia, the UK, and Argentina) to maximise the area for fireball observation time and therefore meteorite recoveries. The members have a choice to operate independently, but they can also choose to work in a fully collaborative manner with other GFO partners. This efficient approach leverages the experience gained from the Desert Fireball Network (DFN) pathfinder project in Australia. The state-of-the art technology (DFN camera systems and data reduction) and experience of the support teams is shared between all partners, freeing up time for science investigations and meteorite searching. With all networks combined together, the GFO collaboration already covers 0.6% of the Earth's surface for meteorite recovery as of mid-2019, and aims to reach 2% in the early 2020s. We estimate that after 5 years of operation, the GFO will have observed a fireball from virtually every meteorite type. This combined effort will bring new, fresh, extra-terrestrial material to the labs, yielding new insights about the formation of the Solar System.Comment: Accepted in PSS. 19 pages, 9 figure

A novel organic-rich meteoritic clast from the outer solar system

The Zag meteorite which is a thermally-metamorphosed H ordinary chondrite contains a primitive xenolitic clast that was accreted to the parent asteroid after metamorphism. The cm-sized clast contains abundant large organic grains or aggregates up to 20μm in phyllosilicate-rich matrix. Here we report organic and isotope analyses of a large (~10μm) OM aggregate in the Zag clast. The X-ray micro-spectroscopic technique revealed that the OM aggregate has sp2 dominated hydrocarbon networks with a lower abundance of heteroatoms than in IOM from primitive (CI,CM,CR) carbonaceous chondrites, and thus it is distinguished from most of the OM in carbonaceous meteorites. The OM aggregate has high D/H and 15N/14N ratios (δD=2,370±74‰ and δ15N=696±100‰), suggesting that it originated in a very cold environment such as the interstellar medium or outer region of the solar nebula, while the OM is embedded in carbonate-bearing matrix resulting from aqueous activities. Thus, the high D/H ratio must have been preserved during the extensive late-stage aqueous processing. It indicates that both the OM precursors and the water had high D/H ratios. Combined with 16O-poor nature of the clast, the OM aggregate and the clast are unique among known chondrite groups. We further propose that the clast possibly originated from D/P type asteroids or trans-Neptunian Objects

Nitrogen speciation in upper mantle fluids and the origin of Earth's nitrogen-rich atmosphere

Volatile elements stored in the mantles of terrestrial planets escape through volcanic degassing, and thereby influence planetary atmospheric evolution and habitability. Compared with the atmospheres of Venus and Mars, Earth's atmosphere is nitrogen-rich relative to primordial noble gas concentrations1, 2, 3. The compatibility of volatile elements in mantle minerals versus melts and fluids controls how readily these elements are degassed. However, the speciation of nitrogen in mantle fluids is not well constrained4, 5, 6. Here we present thermodynamic calculations that establish the speciation of nitrogen in aqueous fluids under upper mantle conditions. We find that, under the relatively oxidized conditions of Earth's mantle wedges at convergent plate margins7, 8, 9, nitrogen is expected to exist predominantly as N2 in fluids and, therefore, be degassed easily. In contrast, under more reducing conditions elsewhere in the Earth's upper mantle and in the mantles of Venus and Mars, nitrogen is expected predominantly in the form of ammonium (NH4+) in aqueous fluids. Ammonium is moderately compatible in upper mantle minerals10, 11 and unconducive to nitrogen degassing. We conclude that Earth's oxidized mantle wedge conditions—a result of subduction and hence plate tectonics—favour the development of a nitrogen-enriched atmosphere, relative to the primordial noble gases, whereas the atmospheres of Venus and Mars have less nitrogen because they lack plate tectonics.</p

Magmatic precipitation as a possible origin of Noachian clays on Mars

Hydrous clay minerals detected on the surface of Mars have been interpreted as indicators of the hydrologic and climatic evolution of the planet. The iron- and magnesium-rich clays described in thick, extensive outcrops of Noachian crust have been proposed to originate from aqueous weathering. This would imply that liquid water was stable at the surface of early Mars, presumably when the climate was warmer and wetter. Here we show that iron- and magnesium-rich clays can alternatively form by direct precipitation from residual, water-rich magma-derived fluids. Infrared reflectance spectra from terrestrial lavas from the Mururoa Atoll (French Polynesia) that underwent this precipitation process are similar to those measured for the Noachian crust. Such an origin is also consistent with the D/H ratio of iron- and magnesium-rich clays in some martian meteorites and the widespread presence of these clays in massive basaltic lavas, breccias and regolith. We propose that the progressive degassing of the martian interior over time and the resultant increasingly water-poor magmatic fluids -and not a cooling climate- may explain the absence of clays in Hesperian-aged and more recent formations