Tungsten nuclear anomalies in planetesimal cores

Abstract

Use of the extinct ¹⁸²Hf-¹⁸²W chronometer to constrain the timing of planetary accretion and differentiation rests on the assumption that the solar nebula had homogeneous tungsten isotopic composition. Here, we report deficiencies of ∼0.1 part in 10,000 in the abundance of ¹⁸⁴W in group IVB iron meteorites relative to the silicate Earth. These are most likely due to incomplete mixing at the planetesimal scale (2-4 km radius bodies) of the products of slow (s-) and rapid (r-) neutron-capture nucleosynthesis in the solar nebula. The correction that must be applied to the ¹⁸²Hf- ⁸²W model age of core formation in IVB irons due to the presence of these nuclear anomalies is ∼0.5 Myr. © 2008. The American Astronomical Society. All rights reserved.