|
Shortly
after Siegfried Haberer had secured the first
samples of Almahata Sitta / Asteroid 2008 TC3, I had the opportunity to
inspect
several samples with Siegfried and Dr. Jürgen Otto, a seasoned
meteoriticist
from Freiburg, Germany. It soon became obvious that the recovered
material was
pretty heterogenous, with some samples representing the anomalous
ureilite described by
Jenniskens et al. However, there were also samples which showed much
more texture,
and other samples that didn't look like an ureilite at all.
I
remember that I was taken aback when I inspected a
slice which looked like a light-colored, ultra-fresh equilibrated
chondrite. If
it wasn't for the fact that some samples had shown more than one of
these
lithologies I would have thought that we were looking at different
unrelated
meteorite finds. Could it be that this unusual polymict ureilite was
actually
that polymict? I had never seen anything that weird! Both Dr. Otto and
me urged
Siegfried to have his samples studied further, and I'm more than glad
that he
did. Now if you look at Dr. Bischoff's findings in the following
abstract you
will find out why. Almahata Sitta is not only special because it is the
first
predicted meteorite fall, and it's not only extraordinary because it
represents
an anomalous member of a rare class of achondrites. In fact, its nature
seems
to be much more complicated than that: it seems to represent a fall
comprised
of several meteorite types, including different ureilitic lithologies,
E
chondrites, ordinary chondrites, plus a so-far unknown type of
unequilibrated
chondrite. How can that be?
Just
think of regolith breccias such as howardites or
some polymict eucrites. Some contain clasts of carbonaceous chondrites,
and
other exotic inclusions. The surface areas of meteorite parent bodies -
such as
our own Moon - are constantly bombarded by meteorite impacts, with
meteoritic
material of other types that gets mixed with the original material of
the parent
body to form a surface regolith, a polymict layer of heterogenous
material
which can contain all kinds of stuff. Almahata Sitta / Asteroid 2008
TC3 seems
to represent such a case, a real smorgasbord of different meteorite
types. That
is at least my take at this moment as I have no other explanation as to
why a
polymict asteroid such as 2008 TC3 came into existence in the first
place.
In
any case, Almahata Sitta and its various lithologies
do represent a real bonanza, a stroke of fortune as they allow us to
re-think
what we all believe we know about meteorites and meteorite parent
bodies. The
possible implications are vast and manifold. I immediately thought of
the many
desert strewnfields that we have searched in the past. On several
occasions we
have found several different types of meteorites in more or less the
same place
- something that was easily explained by overlapping strewnfields of
different
meteorite falls. Or maybe not? The case of Alamahata Sitta clearly
shows us
that this is only one explanation that might be true for the majority
of
strewnfields, falls and finds, but it also provides us with a weird
exception,
with the possibility that different meteorite types might arrive within
the
same fall! This is extraordinary and thought-provoking! I'm looking
forward to
future studies on Almahata Sitta which might help to solve all these
mysteries,
and I hope that it will provide us with more answers than with
questions.
Norbert Classen
President of
IMCAInc.
|
