The terrestrial late veneer from core disruption of a lunar-sized impactor

1H.Genda, 1R.Brasser, 2,3S.J.Mojzsis
Earth and Planetary Science Letters 480, 25-32 Link to Article [https://doi.org/10.1016/j.epsl.2017.09.041]
1Earth-Life Science Institute, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro-ku, Tokyo 152-8551, Japan
2Department of Geological Sciences, University of Colorado, UCB 399, 2200 Colorado Avenue, Boulder, CO 80309-0399, USA
3Institute for Geological and Geochemical Research, Research Center for Astronomy and Earth Sciences, Hungarian Academy of Sciences, 45 Budaörsi Street, H-1112 Budapest, Hungary
Copyright Elsevier

Overabundances in highly siderophile elements (HSEs) of Earth’s mantle can be explained by conveyance from a singular, immense (D∼3000km) “Late Veneer” impactor of chondritic composition, subsequent to lunar formation and terrestrial core-closure. Such rocky objects of approximately lunar mass (∼0.01 M⊕) ought to be differentiated, such that nearly all of their HSE payload is sequestered into iron cores. Here, we analyze the mechanical and chemical fate of the core of such a Late Veneer impactor, and trace how its HSEs are suspended – and thus pollute – the mantle. For the statistically most-likely oblique collision (∼45°), the impactor’s core elongates and thereafter disintegrates into a metallic hail of small particles (∼10 m). Some strike the orbiting Moon as sesquinary impactors, but most re-accrete to Earth as secondaries with further fragmentation. We show that a single oblique impactor provides an adequate amount of HSEs to the primordial terrestrial silicate reservoirs via oxidation of (<m-sized) metal particles with a hydrous, pre-impact, early Hadean Earth.

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