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Post Info TOPIC: Solar supernova


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RE: Solar supernova
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A strange mix of oxygen found in a stony meteorite that exploded over Pueblito de Allende, Mexico nearly 40 years ago has puzzled scientists ever since. Small flecks of minerals lodged in the stone and thought to date from the beginning of the solar system have a pattern of oxygen types, or isotopes, that differs from those found in all known planetary rocks, including those from Earth, its Moon and meteorites from Mars.

Now scientists from UC San Diego and Lawrence Berkeley National Laboratory have eliminated one model proposed to explain the anomaly: the idea that light from the early Sun could have shifted the balance of oxygen isotopes in molecules that formed after it turned on. When they beamed light through carbon monoxide gas to form carbon dioxide, the balance of oxygen isotopes in the new molecules failed to shift in ways predicted by the model they report in the Sept. 5 issue of Science.

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Iron-60
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Title: Telescopes versus Microscopes: the puzzle of Iron-60
Authors: Jonathan P. Williams

The discovery that the short-lived radionucleide iron-60 was present in the oldest meteorites suggests that the formation of the Earth closely followed the death of a massive star. I discuss three astrophysical origins: winds from an AGB star, injection of supernova ejecta into circumstellar disks, and induced star formation on the boundaries of HII regions. I show that the first two fail to match the solar system iron-60 abundance in the vast majority of star forming systems. The cores and pillars on the edges of HII regions are spectacular but rare sites of star formation and larger clumps with masses 1e3-1e4 solar masses at tens of parsec from a supernova are a more likely birth environment for our Sun. I also examine gamma-ray observations of iron-60 decay and show that the Galactic background could account for the low end of the range of meteoritic measurements if the massive star formation rate was at least a factor of 2 higher 4.6 Gyr ago.

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RE: Solar supernova
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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: Oxygen isotope anomalies of the Sun and the original environment of the Solar system
Authors: Jeong-Eun Lee, Edwin A. Bergin, James R. Lyons
(Version v3)

We present results from a model of oxygen isotopic anomaly production through selective photodissociation of CO within the collapsing proto-Solar cloud. Our model produces a proto-Sun with a wide range of Delta_17O values depending on the intensity of the ultraviolet radiation field. Dramatically different results from two recent Solar wind oxygen isotope measurements indicate that a variety of compositions remain possible for the solar oxygen isotope composition. However, constrained by other measurements from comets and meteorites, our models imply the birth of the Sun in a stellar cluster with an enhanced radiation field and are therefore consistent with a supernova source for 60Fe in meteorites.

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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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Solar system was born 4568 million yrs ago.
A new research has dated the earliest step in the formation of the solar system when microscopic interstellar dust combined into mountain-sized chunks of rock to 4,568 million years.

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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.

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Title: Is our Sun a Singleton?
Authors: D. Malmberg, M. B. Davies, J. E. Chambers, F. De Angeli, R. P. Church, D. Mackey, M. I. Wilkinson

Most stars are formed in a cluster or association, where the number density of stars can be high. This means that a large fraction of initially-single stars will undergo close encounters with other stars and/or exchange into binaries. We describe how such close encounters and exchange encounters can affect the properties of a planetary system around a single star. We define a singleton as a single star which has never suffered close encounters with other stars or spent time within a binary system. It may be that planetary systems similar to our own solar system can only survive around singletons. Close encounters or the presence of a stellar companion will perturb the planetary system, often leaving planets on tighter and more eccentric orbits. Thus planetary systems which initially resembled our own solar system may later more closely resemble some of the observed exoplanet systems.

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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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The formation of our solar system
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We know that our solar system has at least one planet with life Earth. Perhaps solar systems that formed in ways similar to our own also will have the potential for life. But how normal was the formation of our solar system? In Astrobiology Magazine, European Edition, Thierry Montmerle suggests our solar system had an unusually violent origin.

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