We have analyzed molybdenum isotopes, together with strontium and barium isotopes, in 18 presolar silicon carbide grains using the Chicago Instrument for Laser Ionization (CHILI), a resonance ionization mass spectrometer. All observed isotope ratios can be explained by mixtures of pure s-process matter with isotopically solar material. Grain residues were subsequently analyzed for carbon, nitrogen, silicon, and sulfur isotopes, as well as a subset for 26Al–26Mg systematics using the NanoSIMS. These analyses showed that all but one grain are mainstream grains, most probably coming from low-mass asymptotic giant branch (AGB) stars. One grain is of the AB type, for which the origin is still a matter of debate. The high precision of molybdenum isotope measurements with CHILI provides the best estimate to date for s-process molybdenum made in low-mass AGB stars. The average molybdenum isotopic abundances produced by the s-process found in the analyzed mainstream SiC grains are 0% 92Mo, 0.73% 94Mo, 13.30% 95Mo, 36.34% 96Mo, 9.78% 97Mo, 39.42% 98Mo, and 0.43% 100Mo. Solar molybdenum can be explained as a combination of 45.9% s-process, 30.6% r-process, and 23.5% p-process contributions. Furthermore, the observed variability in the individual grain data provides insights into the variability of conditions (neutron density, temperature, and timescale) during s-process nucleosynthesis in the grains’ parent stars, as they have subtle effects on specific molybdenum isotope ratios. Finally, the results suggest that the ratio between p- and r-process molybdenum in presolar SiC from many different types of parent stars is Mo p /Mo r  = 0.767, the value inferred for the solar system and consistent with what has been found in bulk samples and leachates of primitive meteorites.

Establishing the abundance of the extinct radionuclide 60Fe (half-life 2.62 Ma) in the early solar system is important for understanding the astrophysical context of solar system formation. While bulk measurements of early solar system phases show a low abundance consistent with galactic background, some in situ measurements by secondary ion mass spectrometry (SIMS) imply a higher abundance, which would require injection from a nearby supernova (SN). Here we present in situ nickel isotopic analyses by resonance ionization mass spectrometry (RIMS) in a chondrule from the primitive meteorite Semarkona (LL3.00). The same chondrule had been previously analyzed by SIMS. Despite improved precision compared to SIMS, the RIMS nickel isotopic data do not reveal any resolved excesses of 60Ni that could be unambiguously ascribed to in situ 60Fe decay. Linear regression of 60Ni/58Ni versus 56Fe/58Ni yields an initial 60Fe/56Fe ratio for this chondrule of (3.8 ± 6.9) × 10−8, which is consistent with both the low initial value found by bulk measurements and the low end of the range of initial ratios inferred from some in situ work. The same regression also gives a solar initial 60Ni/58Ni ratio, which shows that this sample was not disturbed by nickel mobilization, thus agreeing with a low initial 60Fe/56Fe ratio. These findings agree with a re-evaluation of previous SIMS measurements of the same sample. Supernova injection of 60Fe into the solar system or its parental cloud material is therefore not necessary to account for the measured solar system’s initial amount of 60Fe.

Understanding Hadean (>4 Ga) Earth requires knowledge of its crust. The composition of the crust and volatiles migrating through it directly influence the makeup of the atmosphere, the composition of seawater, and nutrient availability. Despite its importance, there is little known and less agreed upon regarding the nature of the Hadean crust. By analyzing the Sr/Sr ratio of apatite inclusions in Archean zircons from Nuvvuagittuq, Canada, we show that its protolith had formed a high (>1) Rb/Sr ratio reservoir by at least 4.2 Ga. This result implies that the early crust had a broad range of igneous rocks, extending from mafic to highly silicic compositions.

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