Mesosiderite formation on asteroid 4 Vesta by a hit-and-run collision

Abstract

Collision and disruption processes of proto-planetary bodies in the early solar system are key to understanding the genesis of diverse types of main-belt asteroids. Mesosiderites are stony-iron meteorites that formed by mixing of howardite-eucrite-diogenite-like crust and molten core materials and provide unique insights into the catastrophic break-up of differentiated asteroids. However, the enigmatic formation process and the poorly constrained timing of metal-silicate mixing complicate the assignment to potential parent bodies. Here we report high-precision uranium-lead dating of mesosiderite zircons by isotope dilution thermal ionization mass spectrometry, revealing initial crust formation 4,558.5 ± 2.1 million years ago and metal-silicate mixing at 4,525.39 ± 0.85 million years.The two distinct ages coincide with the timing of crust formation and a large-scale reheating event on the eucrite parent body, likely the asteroid Vesta. This chronological coincidence corroborates that Vesta is the parent body of mesosiderite silicates.Mesosiderite formation on Vesta can be explained by a hit-and-run collision 4,525.4 million years ago that caused the thick crust observed by NASA's Dawn mission and explains the missing olivine in mesosiderites, howardite-eucrite-diogenite meteorites, and vestoids.

In situ Pb‐Pb dating of silica‐rich Northwest Africa (NWA) 6594 basaltic eucrite and its constraint on thermal history of the Vestan crust

“…9; Yamaguchi et al 2002;Schwartz and McCallum 2005). However, Haba et al (2019) reported Pb-Pb ages of 4525.4 AE 0.9 Ma for mesosiderite zircons, which is consistent with the 4523 AE 2 Ma metamorphic age of NWA 6594 with high precision. They suggest that the 4525.4 AE 0.9 Ma event was induced by a giant impact that led to metal-silicate mixing and formation of mesosiderites, which may also be related to a large-scale reheating event on Vesta.…”

Accretion of the Earth—Missing Components?

“…The initial 142 Nd abundance for Vesta was estimated from internal mineral isochrons of basaltic and cumulative eucrites (Boyet et al 2010 and references therein). These meteorites have a similar isotopic evolution as angrites and in particular mesosiderites, which is also reflected in the similarity of U-Pb ages of zircons separated from these meteorites (Haba et al 2019). Their 146 Sm-142 Nd evolution, when compared with the crystallization ages, is most consistent with a source that had a composition similar to ordinary chondrites (Gannoun et al 2011).…”

Two generations of exsolution lamellae in pyroxene from Asuka 09545: Clues to the thermal evolution of silicates in mesosiderite

“…The metal component shows some similarities to IIIAB iron meteorites (Hassanzadeh, et al 1990), whereas the silicate fraction has been compared with basaltic or pyroxenitic Howardite-Eucrite-Diogenite (HED) meteorites (e.g., Clayton and Mayeda 1996;Greenwood et al 2015). A common origin of the silicate fraction of mesosiderites and the HED from the asteroid 4-Vesta has been disproved (Rubin and Mittlefehldt 1993) and recently proposed again (Haba et al 2019). The simultaneous presence of silicate and metal is interpreted as a mixture of basaltic material from the crust and metal from the core, originating either by collision of two differentiated parent bodies (Wasson and Rubin 1985) or from mixing within the same parent body (Mittlefehldt et al 1998;Scott et al 2001).…”