Hypervelocity collision and water-rock interaction in space preserved in the Chelyabinsk ordinary chondrite

Abstract

A comprehensive geochemical study of the Chelyabinsk meteorite reveals further details regarding its history of impact-related fragmentation and melting, and later aqueous alteration, during its transit toward Earth. We support an ∼30 Ma age obtained by Ar-Ar method (Beard et al. , 2014) for the impact-related melting, based on Rb-Sr isotope analyses of a melt domain. An irregularly shaped olivine with a distinct O isotope composition in a melt domain appears to be a fragment of a silicate-rich impactor. Hydrogen and Li concentrations and isotopic compositions, textures of Fe oxyhydroxides, and the presence of organic materials located in fractures, are together consistent with aqueous alteration, and this alteration could have pre-dated interaction with the Earth’s atmosphere. As one model, we suggest that hypervelocity capture of the impact-related debris by a comet nucleus could have led to shock-wave-induced supercritical aqueous fluids dissolving the silicate, metallic, and organic matter, with later ice sublimation yielding a rocky rubble pile sampled by the meteorite.

The Albedo of Ryugu: Evidence for a High Organic Abundance, as Inferred from the Hayabusa2 Touchdown Maneuver

“…Sublimation could also concentrate the nonvolatile MOM at the surface of Ryugu and possibly within cracks and cavities in its interior, in a similar way to freeze-drying (e.g., Hoang et al, 2019). Therefore, the potentially high organic abundance, visible albedo, and rubble-pile nature of Ryugu may originate from interactions between rocky and icy solar bodies, in a similar way to the model proposed for the Chelyabinsk meteorite (Nakamura et al, 2019). Such a scenario for the formation of Ryugu has an advantage over other suggestions, because it can explain both the IDP-like albedo and potentially high organic content of Ryugu, as well as the presence of partially hydrated material that could constitute the boulders observed on its surface and likely within its interior.…”

“…Indeed, Vernazza et al ( 2015 ) described Cb-type asteroids as comet-like. The parent body of the Chelyabinsk meteorite has been indicated as a comet that captured debris resulting from a high-velocity collision, thus forming a rubble pile after water ice sublimation (Nakamura et al, 2019 ). The presence of organic matter (Popova et al, 2013 ) and evidence of aqueous alteration were found within the Chelyabinsk meteorite, which were indicated as the result of interactions between the cometary ice and organic matter and the captured silicate minerals (Nakamura et al, 2019 ).…”

“…The parent body of the Chelyabinsk meteorite has been indicated as a comet that captured debris resulting from a high-velocity collision, thus forming a rubble pile after water ice sublimation (Nakamura et al, 2019 ). The presence of organic matter (Popova et al, 2013 ) and evidence of aqueous alteration were found within the Chelyabinsk meteorite, which were indicated as the result of interactions between the cometary ice and organic matter and the captured silicate minerals (Nakamura et al, 2019 ). If we apply the same scenario to Ryugu, it may help explain the presence of high organic matter abundances at the surface and the presence of CM-like fragments (the boulders), which could have become partially aqueously altered.…”

The asteroid 162173 Ryugu: a cometary origin

“…However, the collisional reaccumulation scenario does not explain the origin of the abundant organic matter. An alternative scenario is that Ryugu is an extinct comet, which lost its icy components [2,6,3]. Here, the sublimation of water ice from a uniform porous cometary nucleus was numerically simulated until the refractory components, such as silicate rocks and organic matter were left behind as evapora-…”

“…An alternative scenario, which can satisfy the three different major features of the asteroid Ryugu simultaneously, is a cometary origin [2,6,3].…”