Neutron-rich isotopes with masses near that of iron are produced in type Ia and II supernovae. Traces of such nucleosynthesis are found in primitive meteorites in the form of variations in the isotopic abundance of 54 Cr, the most neutron-rich stable isotope of chromium.The hosts of these isotopic anomalies must be presolar grains that condensed in the outflows of supernovae, offering the opportunity to study the nucleosynthesis of iron-peak nuclei in ways that complement spectroscopic observations and can inform models of stellar evolution. However, despite almost two decades of extensive search, the carrier of 54 Cr anomalies is still unknown, presumably because it is fine-grained and is chemically labile. Here we identify in the primitive meteorite Orgueil the carrier of 54 Cr-anomalies as nanoparticles, most likely spinels that show large enrichments in 54 Cr relative to solar composition ( 54 Cr/ 52 Cr ratio >3.6×solar). Such large enrichments in 54 Cr can only be produced in supernovae. The mineralogy of the grains supports condensation in the O/Ne-O/C zones of a type II supernova, although a type Ia origin cannot beexcluded. We suggest that planetary materials incorporated different amounts of these nanoparticles, possibly due to late injection by a nearby supernova that also delivered 26 Al and 60 Fe to the solar system. This idea explains why the relative abundance of 54 Cr and other neutronrich isotopes vary between planets and meteorites. We anticipate that future isotopic studies of the grains identified here will shed new light on the birth of the solar system and the conditions in supernovae.

We report the petrology, O isotopic composition, and Al-Mg isotope systematics of a chondrule fragment from the Jupiter-family comet Wild 2, returned to Earth by NASA's Stardust mission. This object shows characteristics of a type II chondrule that formed from an evolved oxygen isotopic reservoir. No evidence for extinct 26 Al was found, with ( 26 Al/ 27 Al) 0 < 3.0×10 −6 . Assuming homogenous distribution of 26 Al in the solar nebula, this particle crystallized at least 3 Myr after the earliest solar system objects-relatively late compared to most chondrules in meteorites. We interpret the presence of this object in a Kuiper Belt body as evidence of late, large-scale transport of small objects between the inner and outer solar nebula. Our observations constrain the formation of Jupiter (a barrier to outward transport if it formed further from the Sun than this cometary chondrule) to be more than 3 Myr after calcium-aluminum-rich inclusions.

Interstellar dust (ISD) from the local interstellar medium (LISM) streams into the solar system from approximately the direction of the constellation Ophiuchus. Prior to the return of the NASA Stardust spacecraft (1) no recognizable samples of this interstellar dust were available for laboratory study. Thus, our understanding of the properties of contemporary ISD has been derived primarily from astronomical observations of the ISM, including optical properties of the ISD and remote spectroscopy of the gas composition (2-4), and from in situ measurements by the dust analyzers on the Cassini, Ulysses and Galileo spacecraft (5-7). The canonical picture of ISD is that it is dominated by ~0.2 µm diameter (8) amorphous silicate grains, with or without carbonaceous mantles. However, the inferred properties of the particles, including size distribution, density and composition are heavily model dependent.