Already famous for its collection of amino acids, Murchison meteorite has just delivered a new data on the formation of the nebula protosolaire. Dust which constituted it floated in interstellar space for a much shorter time than imagined.

Fell on 28 September 1969 near the town of Murchison in Australia, one hundred kilometers north of Melbourne, the famous meteorite that bears the name of this village is not only a gold mine for exobiology. Indeed, the Murchison meteorite does not make that to embark amino acids supporting the hypothesis of an input primitive prebiotic compounds on the young Earth by meteorite bombardment of Hadéen (first part of the Precambrian era), it also contains grains présolaires.

Like its cousin, Allende, the Murchison meteorite is a carbonaceous chondrite, which makes it a precious memory of the physicochemical conditions prevailing in the nebula protosolaire.

If one knows how to take the analysis of isotopes in the grains and dust embedded in a meteorite can make it very talkative. That is what shows once more with the work of Philipp R. Heck and his colleagues. With the mass spectrometer of the Chicago Center for Cosmochemistry, researchers determined the concentration of atoms of neon and helium in 22 grains présolaires in the Murchison meteorite.

A supernova origin of the Sun

These concentrations are important to know because under the action of cosmic rays traveling through the Galaxy, which is known and estimate the flow, they are changing within the grains of dust and evolve as a function of time spent living in the interstellar medium . In this way, we can estimate the time elapsed between the formation of a grain of dust in the atmosphere of a giant at the end of life and information on its inclusion in a meteorite in a protoplanetary disk.

The models of cosmochemistry and astrophysicists led to an average residence time of 500 million years. But this is not what Heck and his colleagues have found ..

17 grains were visibly présolaires remained in the interstellar medium as a few million years to 200 million years at most. This result is instructive on the formation of our solar system.

It seems compatible with the hypothesis of a supernova that have accelerated the collapse of a small molecular cloud over 4.56 billion years. A period of intense star formation prior to explain the dispersion found in times of residence in the interstellar environment of the grains of the meteorite of Murchison.

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