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Abstract This study conducts mineralogical and chemical investigations on the oldest achondrite, Erg Chech 002 (∼4565 million yr old). This meteorite exhibits a disequilibrium igneous texture characterized by high-Mg-number (atomic Mg/(Mg + Fe²⁺)) orthopyroxene xenocrysts (Mg number = 60–80) embedded in an andesitic groundmass. Our research reveals that these xenocrysts were early formed crystals, loosely accumulated or scattered in the short-period magma ocean on the parent body. Subsequently, these crystals underwent agitation due to the influx of external materials. The assimilation of these materials enriched the¹⁶O component of the magma ocean and induced a relatively reduced state. Furthermore, this process significantly cooled the magma ocean and inhibited the evaporation of alkali elements, leading to elevated concentrations of Na and K within the meteorite. Our findings suggest that the introduced materials are probably sourced from the reservoirs of CR clan meteorites, indicating extensive transport and mixing of materials within the early solar system. 

Abstract We investigated the hydrogen isotopic compositions and water contents of pyroxenes in two recent ordinary chondrite falls, namely, Chelyabinsk (2013 fall) and Benenitra (2018 fall), and compared them to three ordinary chondrite Antarctic finds, namely, Graves Nunataks GRA 06179, Larkman Nunatak LAR 12241, and Dominion Range DOM 10035. The pyroxene minerals in Benenitra and Chelyabinsk are hydrated (∼0.018–0.087 wt.% H 2 O) and show D-poor isotopic signatures ( δ D SMOW from −444‰ to −49‰). On the contrary, the ordinary chondrite finds exhibit evidence of terrestrial contamination with elevated water contents (∼0.039–0.174 wt.%) and δ D SMOW values (from −199‰ to −14‰). We evaluated several small parent-body processes that are likely to alter the measured compositions in Benenitra and Chelyabinsk and inferred that water loss in S-type planetesimals is minimal during thermal metamorphism. Benenitra and Chelyabinsk hydrogen compositions reflect a mixed component of D-poor nebular hydrogen and water from the D-rich mesostases. A total of 45%–95% of water in the minerals characterized by low δ D SMOW values was contributed by nebular hydrogen. S-type asteroids dominantly composed of nominally anhydrous minerals can hold 254–518 ppm of water. Addition of a nebular water component to nominally dry inner solar system bodies during accretion suggests a reduced need of volatile delivery to the terrestrial planets during late accretion. 

Abstract Recent studies have detected structurally bound water in the refractory silicate minerals present in ordinary and enstatite chondrite meteorites. The mechanism for the incorporation of the hydrogen is not well defined. In this paper we quantitatively examine a two-fold process involving the implantation and diffusion of nebular hydrogen ions that is responsible for the hydration of the chondritic minerals. Our simulations show that depending on critical parameters, including the flux of the protons in nebular plasma, retention coefficient, temperature of the silicate minerals, and desorption rate of implanted hydrogen, the implantation of low-energy hydrogen ions can result in equivalent water contents of ∼0.1 wt% in chondritic silicates within 10 years. Thus, this novel mechanism operating in the nebula at 10 −3 bar pressure and <650 K temperatures can efficiently hydrate the free-floating chondritic minerals prior to the rapid formation of planetesimals inside the snow line, and agree well with the wet accretion scenario for the inner solar system objects. 

We performed the first measurements of hydrogen isotopic composition and water content in nominally anhydrous minerals collected by the Hayabusa mission from the S-type asteroid Itokawa. The hydrogen isotopic composition (δD) of the measured pyroxene grains is −79 to −53‰, which is indistinguishable from that in chondritic meteorites, achondrites, and terrestrial rocks. Itokawa minerals contain water contents of 698 to 988 parts per million (ppm) weight, after correcting for water loss during parent body processes and impact events that elevated the temperature of the parent body. We infer that the Bulk Silicate Itokawa parent body originally had 160 to 510 ppm water. Asteroids like Itokawa that formed interior to the snow line could therefore have been a potential source of water (up to 0.5 Earth’s oceans) during the formation of Earth and other terrestrial planets.