* Astronomy

Title: Iron-60 evidence for early injection and efficient mixing of stellar debris in the protosolar nebula
Authors: N. Dauphas, D.L. Cook, A. Sacarabany, C. Frohlich, A.M. Davis, M. Wadhwa, A. Pourmand, T. Rauscher, R. Gallino

 Among extinct radioactivities present in meteorites, 60Fe (t1/2 = 1.49 Myr) plays a key role as a high-resolution chronometer, a heat source in planetesimals, and a fingerprint of the astrophysical setting of solar system formation. A critical issue with 60Fe is that it could have been heterogeneously distributed in the protoplanetary disk, calling into question the efficiency of mixing in the solar nebula or the timing of 60Fe injection relative to planetesimal formation. If this were the case, one would expect meteorites that did not incorporate 60Fe (either because of late injection or incomplete mixing) to show 60Ni deficits (from lack of 60Fe decay) and collateral effects on other neutron-rich isotopes of Fe and Ni (coproduced with 60Fe in core-collapse supernovae and AGB-stars). Here, we show that measured iron meteorites and chondrites have Fe and Ni isotopic compositions identical to Earth. This demonstrates that 60Fe must have been injected into the protosolar nebula and mixed to less than 10 % heterogeneity before formation of planetary bodies.

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Title: Indigenous amino acids in primitive CR meteorites
Authors: Z.Martins, C.M.O'D.Alexander, G.E.Orzechowska, M.L.Fogel, P.Ehrenfreund

CR meteorites are among the most primitive meteorites. In this paper, we report the first measurements of amino acids in Antarctic CR meteorites, two of which show the highest amino acid concentrations ever found in a chondrite. EET92042, GRA95229 and GRO95577 were analysed for their amino acid content using high performance liquid chromatography with UV fluorescence detection (HPLC-FD) and gas chromatographymass spectrometry (GC-MS). Our data show that EET92042 and GRA95229 are the most amino acid-rich chondrites ever analysed, with total amino acid concentrations ranging from 180 parts-per-million (ppm) to 249 ppm. GRO95577, however, is depleted in amino acids. The most abundant amino acids present in the EET92042 and GRA95229 meteorites are the alpha-amino acids glycine, isovaline, alpha-aminoisobutyric acid (alpha-AIB), and alanine, with delta13C values ranging from +31.6per mil to +50.5per mil. The carbon isotope results together with racemic enantiomeric ratios determined for most amino acids strongly indicate an extraterrestrial origin of these compounds. In addition, the relative abundances of alpha-AIB and beta-alanine in the Antarctic CR meteorites analysed appear to correspond to the degree of aqueous alteration on their respective parent body.

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Ancient sea mud records supernova blast
It is the oldest telescope in the world - and it lies at the bottom of the ocean. Ancient sea floor sediments have revealed that a supernova exploded during the Pliocene era and may have caused a minor extinction event on Earth.
Levels of radioactive iron-60 suggest the supernova was between 60 and 300 light years away, says Brian Fields of the University of Illinois at Urbana-Champaign.

"It didn't hit us or we wouldn't be here."

Radiation from the blast could have weakened Earth's atmosphere, he says, exposing organisms to the sun's ultraviolet radiation. This coincides with an extinction peak, but Fields says there is no direct evidence of a link. The work was reported at a meeting of the Geological Society of America in Denver, Colorado, this week.

Source

Astronomic observations with the latest and greatest telescopes are leading astronomers to embrace the idea that stars usually form in clusters, even if they end up, like our Sun, isolated from other stars. Cosmochemists using optical microscopes, electron microscopes, and mass spectrometers are finding evidence supporting the idea, along with important details about the star-forming regions and about the earliest history of the Solar System. The latest breakthrough is reported by Martin Bizzarro and his colleagues at the Geological Institute and Geological Museum in Denmark, at the University of Texas, and at Clemson University in South Carolina. They made high-precision measurements of iron and nickel isotopes.

The results show that the oldest planetesimals to form in the solar system did not contain any iron-60 ( ⁶⁰Fe), which decays to nickel-60 ( ⁶⁰Ni) with a half-life of only 1.5 million years, yet somewhat younger materials did contain it. In contrast, aluminum-26 ( ²⁶Al), with a half-life of 740,000 years, was relatively uniformly distributed.

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