Half-life and initial Solar System abundance of 146Sm determined from the oldest andesitic meteorite

The initial solar system abundance of 60Fe and early core formation of the first asteroids

High-precision Ni isotope analyses of the differentiated andesitic meteorite Erg Chech 002 (EC 002), the oldest known crustal fragment of a planetesimal, show that short-lived 60Fe was present in the early solar system with an initial 60Fe/56Fe ratio of (7.71 ± 0.47) × 10-9, which is five times more precise than previous estimates and is proposed to be the reference value for further studies. Using this ratio, the Ni isotopic composition of EC 002 implies that metal segregation in the source of the EC 002 parental melts took place [Formula: see text] million years (Myr) after solar system formation, and similar very early metal-silicate differentiation ages are obtained for 4-Vesta ([Formula: see text] Myr) and the angrite parent body ([Formula: see text] Myr). Such an early age dictates a specific accretion and differentiation history for the EC 002 parent body, with metal segregation occurring at relatively low temperatures (1000° to 1200°C), followed by a high-temperature silicate melting event.

The 146 Sm half-life re-measured: consolidating the chronometer for events in the early Solar System

The half-life of the extinct radiolanthanide146 Sm , important for both geochronological and astrophysical applications, was re-determined by a combination of mass spectrometry and α -decay counting. Earlier studies provided only limited information on all potential factors that could influence the quantification of the half-life of146 Sm . Thus, special attention was given  here to a complete documentation of all experimental steps to provide information about any possible artifacts in the data analysis. The half-life of146 Sm was derived to be 92.0 Ma ± 2.6 Ma, with an uncertainty coverage factor of k = 1 .

A 4,565-My-old record of the solar nebula field

Magnetic fields in protoplanetary disks are thought to play a prominent role in the formation of planetary bodies. Acting upon turbulence and angular momentum transport, they may influence the motion of solids and accretion onto the central star. By searching for the record of the solar nebula field preserved in meteorites, we aim to characterize the strength of a disk field with a spatial and temporal resolution far superior to observations of extrasolar disks. Here, we present a rock magnetic and paleomagnetic study of the andesite meteorite Erg Chech 002 (EC002). This meteorite contains submicron iron grains, expected to be very reliable magnetic recorders, and carries a stable, high-coercivity magnetization. After ruling out potential sources of magnetic contamination, we show that EC002 most likely carries an ancient thermoremanent magnetization acquired upon cooling on its parent body. Using the U-corrected Pb-Pb age of the meteorite's pyroxene as a proxy for the timing of magnetization acquisition, we estimate that EC002 recorded a field of 60 ± 18 µT at a distance of ~2 to 3 astronomical units, 2.0 ± 0.3 My after the formation of calcium-aluminum-rich inclusions. This record can only be explained if EC002 was magnetized by the field prevalent in the solar nebula. This makes EC002's record, particularly well resolved in time and space, one of the two earliest records of the solar nebula field. Such a field intensity is consistent with stellar accretion rates observed in extrasolar protoplanetary disks.

Igneous meteorites suggest Aluminium-26 heterogeneity in the early Solar Nebula

The short-lived radionuclide aluminium-26 (26Al) isotope is a major heat source for early planetary melting. The aluminium-26 - magnesium-26 (26Al-26Mg) decay system also serves as a high-resolution relative chronometer. In both cases, however, it is critical to establish whether 26Al was homogeneously or heterogeneously distributed throughout the solar nebula. Here we report a precise lead-207 - lead-206 (207Pb-206Pb) isotopic age of 4565.56 ± 0.12 million years (Ma) for the andesitic achondrite Erg Chech 002. Our analysis, in conjunction with published 26Al-26Mg data, reveals that the initial 26Al/27Al in the source material of this achondrite was notably higher than in various other well-preserved and precisely dated achondrites. Here we demonstrate that the current data clearly indicate spatial heterogeneity of 26Al by a factor of 3-4 in the precursor molecular cloud or the protoplanetary disk of the Solar System, likely associated with the late infall of stellar materials with freshly synthesized radionuclides.

Earth's composition was modified by collisional erosion

The samarium-146 (¹⁴⁶Sm)-neodymium-142 (¹⁴²Nd) short-lived decay system (half-life of 103 million years) is a powerful tracer of the early mantle-crust evolution of planetary bodies. However, an increased ¹⁴²Nd/¹⁴⁴Nd in modern terrestrial rocks relative to chondrite meteorites has been proposed to be caused by nucleosynthetic anomalies, obscuring early Earth's differentiation history. We use stepwise dissolution of primitive chondrites to quantify nucleosynthetic contributions on the composition of chondrites. After correction for nucleosynthetic anomalies, Earth and the silicate parts of differentiated planetesimals contain resolved excesses of ¹⁴²Nd relative to chondrites. We conclude that only collisional erosion of primordial crusts can explain such compositions. This process associated with planetary accretion must have produced substantial loss of incompatible elements, including long-term heat-producing elements such as uranium, thorium, and potassium.