Heavy nitrogen in Bencubbin—a light-element isotopic anomaly in a stony-iron meteorite

Abstract

Until now, light-element isotopic anomalies have been confined to primitive chondritic meteorites. Bencubbin, an unusual breccia found in Australia, comprising 60–75% metal with silicate and chondritic clasts^1–4 in a shock-welded matrix^5,6, has been shown^7–9 to contain an unprecedented enrichment (by a factor of 2) of ¹⁵N, presumably a nucleosynthetic product which escaped homogeniz-ation in the solar nebula. Here we show that virtually all the nitrogen in Bencubbin is enriched, with a maximum δ¹⁵N of +1,033‰. The nitrogen resides in two acid-resistant components, one more so than the other, which are present in different proportions in the metal and silicate. The more resistant component could be carbonaceous, with an unusually low C:N ratio and without an anomalous carbon isotopic composition (δ¹³C ≃ +25%‰). Another possible host is a chromium-rich sulphide, which would indicate processing in a supernova¹⁰.