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Abstract-Asteroid 2008 TC 3 impacted Earth in northern Sudan on October 7, 2008. The meteorite named Almahata Sitta was classified as a polymict ureilite. In this study, 40 small pieces from different fragments collected in the Almahata Sitta strewn field were investigated and a large number of different lithologies were found. Some of these fragments are ureilitic in origin, whereas others are clearly chondritic. As all are relatively fresh (W0-W0 ⁄ 1) and as short-lived cosmogenic radioisotopes were detected within two of the chondritic fragments, there is strong evidence that most, if not all belong to the Almahata Sitta meteorite fall. The fragments can roughly be subdivided into achondritic (ureilitic; 23 samples) and chondritic lithologies (17 samples). Among the ureilitic rocks are at least 10 different lithologies. A similar number of different chondritic lithologies also exist. Most chondritic fragments belong to at least seven different E-chondrite rock types (EH3, EL3 ⁄ 4, EL6, EL breccias, several different types of EL and EH impact melt rocks and impact melt breccias; some of the latter are shock-darkened). In addition, two H-group ordinary chondrite lithologies were identified, and one sample of a chondrite type that is so far unique. The latter has some affinities to R chondrites. Oxygen isotope compositions of 14 fragments provide further fundamental information on the lithological heterogeneity of the Almahata Sitta meteorite. Based on the findings presented in this study, the reflectance spectrum of asteroid 2008 TC 3 has to be evaluated in a new light.

23It is now recognized that variations in the Δ 17 O of terrestrial materials resulting from 24 purely mass dependent fractionations, though small, have geological significance. In this study, 25 the  18 O and  17 O values of selected low temperature quartz and silica samples were measured in 26 order to derive the quartz-water fractionation -temperature relationship for the three oxygen 27 isotope system. A 18 O/ 16 O quartz-water fractionation equation valid for all temperatures was 28 generated from published high temperature exchange experiments and low temperature empirical 29 estimates and is given by T T ln

Carbonaceous meteorites are thought to be fragments of C-type (carbonaceous) asteroids. Samples of the C-type asteroid (162173) Ryugu were retrieved by the Hayabusa2 spacecraft. We measure the mineralogy, bulk chemical and isotopic compositions of Ryugu samples. They are mainly composed of materials similar to carbonaceous chondrite meteorites, particularly the CI (Ivuna-type) group. The samples consist predominantly of minerals formed in aqueous fluid on a parent planetesimal. The primary minerals were altered by fluids at a temperature of 37 ± 10°C, 5.2 − 0.8 + 0.7 (Stat.) − 2.1 + 1.6 (Syst.) million years after formation of the first solids in the Solar System. After aqueous alteration, the Ryugu samples were likely never heated above ~100°C. The samples have a chemical composition that more closely resembles the Sun’s photosphere than other natural samples do.

The Moon was probably formed by a catastrophic collision of the proto-Earth with a planetesimal named Theia. Most numerical models of this collision imply a higher portion of Theia in the Moon than in Earth. Because of the isotope heterogeneity among solar system bodies, the isotopic composition of Earth and the Moon should thus be distinct. So far, however, all attempts to identify the isotopic component of Theia in lunar rocks have failed. Our triple oxygen isotope data reveal a 12 ± 3 parts per million difference in Δ(17)O between Earth and the Moon, which supports the giant impact hypothesis of Moon formation. We also show that enstatite chondrites and Earth have different Δ(17)O values, and we speculate on an enstatite chondrite-like composition of Theia. The observed small compositional difference could alternatively be explained by a carbonaceous chondrite-dominated late veneer.