Many people who have seldom looked at chondrules have come up with
imaginative theories of how they formed. The source of heat is just
one aspect of the problem. Most chondrules appear to have been heated
multiple times, an observation difficult to reconcile with this new
model. Many chondrules have had only their outer surfaces melted,
something that seems impossible for the new model to accommodate. The
chondrules in the different chondrite groups have different sizes,
different numbers of rims, different proportions of different textural
types and different O-isotopic compositions. All this indicates that
chondrules formed locally in different regions of the nebula.
Alan Rubin
Quoting Thunder Stone stanleygr...@hotmail.com:
List:
Any thoughts on this?
Greg S.
http://zeenews.india.com/news/space/solar-system-mystery-solved_770352.html
Solar system mystery 'solved'
Washington: Planetary scientists claim they may have discovered how
chondrules, tiny particles found in meteorites, formed at the
beginning of the solar system, thus solving the decades-old cosmic
conundrum.
Chondrules are spherical particles of molten material found in
meteorites but their origins have long been a mystery. No longer
than about one millimetre in diameter, they melted at temperatures
of more than 1,000 degrees Celsius, while the cooler materials
surrounding them only experienced temperatures of a few hundred
degrees Celsius.
Now, an international team, led by Australian National University,
has cracked the mystery as to how chondrules could have actually
formed in extreme heat, especially when the meteorite structure
surrounding them remained cold.
Most of the solar system is cold, so it's been unclear for decades
what caused the chondrules to experience such extreme heat. We
believe that chondrules formed in jets of material ejected from
flattened discs, called 'protostellar discs', which encircle young
stars.
These discs are somewhat like the rings around the planet Saturn.
The modern planets are the remnants of material of these discs
clumping together. In observations of the formation of new stars, we
can see jets of material accelerating out of protostellar discs.
We show that as these jets shoot out of the discs, from about the
Earth-Sun distance away, the materials brought with them are heated
to the point of melting. The heavier items in them then drop back
into the discs, where they cool and re- form, Raquel Salmeron, who
led the team, said.
The scientists said that their theory challenged old assumptions
about the formation of chondrules.
For decades it has been assumed that jets could only form
chondrules through the heating of materials in the vicinity of the
Sun, followed by their transportation into protostellar discs,
Salmeron said in a varsity release.
We believe that our new theory explains how chondrules -- among the
earliest materials in the solar system -- reached the temperatures
required for melting, even though the early solar nebula was cold.
It also explains the fairly uniform size of chondrules and provides
a means for them to mix and combine with unheated material,
Salmeron added.
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