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The formation of Chondrites (French/English)

Ciel & Espace, Novembre 1999, Astroflashes, p. 16: La naissance des
chondrites

La formation du Système solaire, si elle est globalement comprise, n’en
garde pas moins encore ses zones d'ombre.  Comment fabrique-t-on, à
partir de la poussière primordiale rassemblée ça et là en paquets peu
denses, des agrégats compacts de matiére ? Ces agrégats, appelés
chondrites, cailloux riches en fer et en silicates divers, constituent
les briques élémentaires de notre Système, dont il fallait expliquer
I'origine. C'est fait. Deux chercheurs de I'université de Dublin, Brian
McBreen et Lorraine Hanlon, invoquent rien de moins que les sursauts
gamma. Les deux Irlandais ont en effet calcu1é qu’une seule de ces
formidables explosions, survenue dans un rayon de 300 années-lumiére du
Soleil, aurait fondu en petites gouttelettes I'équivalent de 100 masses
terrestres de poussière. Ces gouttelettes se seraient ensuite, en
quelques minutes, agglutinées et refroidies en chondrites. Si cette
explication semble résoudre un vieux probléme, elle diminue en revanche
les possibilités d'existence d'autres systèmes planétaires. En effet,
les sursauts gamma sont relativement rares: seulement une étoile de type
solaire sur mille aurait pu étre exposée à cet arrosage fertilisant de
rayons X et gamma, nécessaire à la naissance des chondrites.

Translation by Bernd Pauli: The birth of chondrites

Although we may have fundamentally understood the formation of the Solar
System, it still retains some poorly understood secrets. How can you
produce solid matter with thin pockets of primordial dust having been
randomly accreted in different parts of the nebula? These aggregates
which are called chondrites and are enriched in iron and various
silicates, make up the fundamental building blocks of our Solar System
the origin of which was still awaiting an explanation. Two researchers
from Dublin University, Brian McBreen and Lorraine Hanlon, have an
answer. For them the culprit are gamma-ray bursts at a distance of 300
light-years [1 LY = 9.46 trillion km] from the sun. Meticulous research
by these two Irish scientists has led them to believe that just one of
these formidable explosions [such gamma-ray bursts are hundreds to
thousands of times more energetic than a supernova but release all their
energy in just a few seconds - the energy thus released is comparable to
the light output of some 20 million billion suns according to an article
by A.M. MacRobert in the May 1999 issue of Sky & Telescope, p. 54]
would in fact have been sufficient to melt the equivalent of 100
terrestrial masses of dust resulting in small droplets. These droplets
would then have agglutinated and cooled within minutes to form the
chondrites. This explanation may resolve an old problem, but, on the
other hand, it diminishes the possibility that other solar systems
exist. Actually, such tremendous gamma-ray bursts are relatively rare
events: just one out of a thousand solar type stars may have been
exposed to such a fertilizing shower of X-rays and gamma-rays,
necessary to trigger the formation of chondrites.

Best regards,

Bernd

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