* Astronomy

Blobrana · L

Murchison meteorite

Blobrana · L

Title: Interstellar Residence Times of Presolar SiC Dust Grains from the Murchison Carbonaceous Meteorite
Authors: Heck, Philipp R.; Gyngard, Frank; Ott, Ulrich; Meier, Matthias M. M.; Avila, Janaína N.; Amari, Sachiko; Zinner, Ernst K.; Lewis, Roy S.; Baur, Heinrich; Wieler, Rainer

The time span between the formation of presolar grains in stellar outflows and their incorporation into early solar-system solids is poorly constrained. Knowledge of this time span is essential for a better understanding of the processing of grains in the interstellar medium (ISM) and formation processes of the solar system. Here, we report interstellar residence times of ~3-1100 Myr for large (~5-50 m) presolar SiC grains, based on their content of He and Ne produced by Galactic cosmic rays. A majority of these grains have interstellar residence times on the order of a few tens up to less than 200 Myr, considerably shorter than theoretical estimates of interstellar dust lifetimes (~500 Myr), but long enough to require formation of the majority of the grains before that of the presolar molecular cloud. The age distribution may be explained by starburst activity 1-2 billion years prior to the birth of the Sun. Our findings provide essential "ground truth" to constrain models of interstellar dust lifetimes and destructive processes in the ISM.

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Blobrana · L

Interstellar Residence Times of Presolar Dust Grains from the Murchison Carbonaceous Meteorite
The interstellar stuff that became incorporated into the planets and life on Earth has younger cosmic roots than theories predict, according to the University of Chicago postdoctoral scholar Philipp Heck and his international team of colleagues.
Heck and his colleagues examined 22 interstellar grains from the Murchison meteorite for their analysis. Dying sun-like stars flung the Murchison grains into space more than 4.5 billion years ago, before the birth of the solar system. Scientists know the grains formed outside the solar system because of their exotic composition.

"The concentration of neon, produced during cosmic-ray irradiation, allows us to determine the time a grain has spent in interstellar space" - Philipp Heck.

His team determined that 17 of the grains spent somewhere between three million and 200 million years in interstellar space, far less than the theoretical estimates of approximately 500 million years. Only three grains met interstellar duration expectations (two grains yielded no reliable age).

"The knowledge of this lifetime is essential for an improved understanding of interstellar processes, and to better contain the timing of formation processes of the solar system" - Philipp Heck.

A period of intense star formation that preceded the sun's birth may have produced large quantities of dust, thus accounting for the timing discrepancy, according to the research team.

University of Chicago

-- Edited by Blobrana on Tuesday 16th of June 2009 04:51:47 PM

Blobrana · L

Tracce di DNA, l' alfabeto della vita, sono state trovate in un frammento di un meteorite caduto in Australia nel 1969. La scoperta, pubblicata da Earth and Planetary Science, confermerebbe l'origine extraterrestre della vita sulla Terra.

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Blobrana · L

On the 28th of September 1969 at a approximately 10.58am a rare type of stony meteorite fell over the township of Murchison, surprisingly causing only minor damage.
The meteorite was moving in a north-westerly direction before impact and exploded over Murchison with fragments falling over an area approximately 11 kms long and 3 kms wide. Although few people saw the fall, most Murchison residents heard it, with the noise likened to thunder or a sonic boom. From Kialla West it was seen as a bright orange ball with a silvery rim and a dull orange tail, leaving a blue smoke trail which lasted for several minutes.

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Blobrana · L

While the Murchison meteorite does not have any once-living material, it is telling researchers new things about how life may have started on Earth, and how that almost universal protein left-handedness came to be.

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Blobrana · L

Scientists from the Department of Earth Science and Engineering at Imperial College have discovered that the Murchison meteorite that hit Australia in 1969 contains the nucleobases, uracil and xanthine. Nucleobases are molecules that are the precursors to RNA and DNA, the basic building blocks of life.

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