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Re: Extra-solar material - comets

Regarding the question:

"Don't the Murchison, Allende and Axtell (and I assume others) meteorites
contain "extra-solar" star dust?"

Hello All,

I was under the impression that Murchison was the only meteorites
(mentioned above and not) which contained true extra-solar grains. While
Allende contains pre-solar material, the CAIs are actually built from
material which existed in our region of space, but just never formally
recycled into our current solar system. The Murchison, on the other hand,
contains material not from this region of space, and in fact, from another
solar system local containing a star 1.2 times as large as our current sun.

Although pre-solar material, and maybe even comets could be considered
"local," the Murchison interstellar grains are not. As far as Axtell goes,
I have no information about it regarding pre or extra-solar origin and
would appreciate some enlightenment.

For those new to this List, there was an series of excellent posts about
the interstellar nature of Murchison. Below is a roughly edited post of the
points made by those involved in the discussion, primarily Frank Stroik. I
agree with Frank, the profoundness of some of the statements here must
cause a rethinking of what consider our comfort-zone in time and space.
After reading the latest measurements of the age of our universe, I wonder
if (assuming the 10.6 by age is even remotely accurate), the interstellar
grains in Murchison are as old as we can get, unless we can undo the
singular nature of the big bang, and play around even farther back in time?

Sincerely,

Martin


The Murchison Carbonaceous Chondrite

We all know of the Murchison carbonaceous chondrite.  Most of us have it in
our collections.  We too, are also aware of amino acids, and organic
compounds found in the meteorite as well. Here is some information on amino
acids in the Murchison meteorite.

1. They are believed to be formed by inorganic processes in the early solar
nebulae.

2.  Life on Earth may have had formed by a gentle layering of organic rich
cometary debris. This would provide a means of getting material through the
atmosphere with out destroying by heat. This only one explanation though,
that adequately argues for life forming by extraterrestrial processes.

3.  There are 79 identified amino acids identified in the Murchison meteorite.

4.  Data indicate that these were formed by low temperature solutions with
water in the parent body of Murchison.

5. And finally, the nature of the amino acids in the Murchison meteorite is
unclear, even after 20 years of research.

Within the last couple of years, research has shown that the Murchison
meteorite also contains an agglomeration of extra-solar grains. These
grains are of a rare chemical solid called silica carbide (SiC).  It has
been found only in diamond deposits here on Earth. The isotope composition
in these grains does not coincide with the Solar System's, but does fit
well with observed data from stars.

These grains probably originated from many different types of stars
including: Wolf-Rayet (These stars are hot, and are expelling dust at an
incredible rate, forming planetary nebulae), Carbon burning stars, Novae
(exploding stars), and Supernovae.  The SiC grains are now being used to
determine the age of the Galaxy we inhabit.

These grains date to about 6 billion years before the origin of the Solar
System. This gives a lower limit on the age of the Milky Way Galaxy of
about 10.5 billion years.  The age of Murchison is still constrained.

The interstellar grains in Murchison are small. They can barely be seen
with the naked eye.  Typically, they are about .002-10 micrometers in size.
There are four main types: 1) Graphite, 2) Diamond, 3) Silicon Carbide, 4)
Corundum, and one less well known type with Silicon bonded to Nitrogen.
These grains are not abundant in the meteorite. There are only about five
to ten grains per gram. They occur in the black matrix, and are not
collected into inclusions as  the CAI's are.

What I am about to say is rather profound. It might be, to me at least, the
single most awe-inspiring concept I have ever encountered. The corundum
grains were formed in a supernovae explosion of a star 1.2 times the size
of our Sun. This is determined by Oxygen isotope ratios that indicate that
these grains were derived from a star with a lower metal content than ours.
This reveals that the star must have been at least 1.2 times larger than
our sun. The age of the grains is determined by the fact that a star with
1.2 times the mass of the Sun, "lives" for about 6 billion years. This
indicates the grains were formed at the end of a star's cycle. Now, to get
the age of the Milky Way, take into account the 4.6 billion year history of
our Solar system, and add it to the fact that the grains formed in the
death of a star with a 6 billion year life. You will come up with a value
of 10.6 billion years. They had to form in the outer arm in which we
inhabit, because if they were from another arm of the galaxy, the distance
would be too far to travel in a few million years.
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