Hi, Graham, List,
They raise that possibility and discuss it (and the
details of that discussion have fallen right out the little
hole in the bottom of my brain where recent knowledge
drains out).
The interesting question (to me) was the possibility
of bodies large enough (like Vesta) to differentiate and
THEN be completely disrupted until the biggest piece
is less than 10 kilometers.
Another consideration is this: there are over 80 unique
iron cores in the Zone; you need that many to produce
all the differing elemental compositions of iron meteorites
we know about. So, there must have been over 80 bodies
big enough to differentiate.
There is a recent study that says these "cores" seem
to have come from the inner solar system, so the guess is
that they were battered to cores there and then the cores
were "migrated" to the Zone by dynamic interactions.
However, it could also be that whole terrestrial planetoids
were displaced to the Zone and battered apart there, and it's
implied by a study like this, that finds some basaltic remains.
Now if they continue and find more (and more) unrelated
basaltic small bodies, one of the questions that arises is "how
big does a body have to be to differentiate?" We know (obviously)
that a body as big as Vesta does, but how about smaller bodies?
Some (by no means all) theorists believe that bodies as small
as 100 kilometers can differentiate.
How could they do that? Well, IF they formed early enough,
they would have enough short-lived isotopes to really get
cooking! At the supernova-mediated start of the solar system,
there were lots of "hot" isotopes available but they decayed very
rapidly. So, the question really is "how fast did planetesimals
and planetoids form?"
Sort of a burning issue in cosmology, actually, the subject of
controversy and the occasional awkward fistfight...
Here's what they say about HED's:
"Regarding this point, the oxygen isotope data
provide evidence that most of the HEDs derive
from a common well-mixed pool. However,
more detailed studies recently indicate that some HEDs
would be inconsistent with a unique origin. Among
these we can mention the eucrites Northwest
Africa 011 (Yamaguchi et al., 2002), Ibitira, Pasamonte,
Caldera and ALHA 78132 (Wiechert et al., 2004).
In particular, the fairly typical eucrite Ibitira has an
17O value indistinguishable from the angrites, which
is another suite of ancient basaltic meteorites. These
meteorites are geochemically distinct from the HEDs
and are clearly resolved on the basis of oxygen isotopes
as well. The meteorite collection could actually represent
several dozen parent bodies, considering also the
abundance of iron meteorites which should have been
part of the nucleus of distinct differentiated bodies
(Burbine et al., 2002). In short, the diversity in the
collection of basaltic meteorites requires more than
one basaltic parent body, which is consistent with
the abundance of differentiated parent bodies implied
by the iron meteorites. In a recent work, Bottke et al.
(2006), demonstrated that small differentiated parent
bodies (and their fragments) should be common in
the Main Belt."
Obviously they lean toward the "small-body" theory.
And, once you got a monstrous amount of data (by going
there probably), you could match basaltic fragments with
their cores by comparing the REE abundances in the irons
with the iron in the basalts...
Sterling K. Webb
---------------------------------------------------------------------
----- Original Message -----
From: "ensoramanda" <[EMAIL PROTECTED]>
To: "Sterling K. Webb" <[EMAIL PROTECTED]>;
<[email protected]>
Sent: Wednesday, August 22, 2007 5:47 PM
Subject: Re: [meteorite-list] Strange Asteroids Baffle Scientists
Hi Sterling/All,
Missed this in April and only just read the recent report.
So does this mean a re-evaluation of the HED group of meteorites that
have up to now been associated with Vesta?
Are there some HED's that show different characteristics and could
therefor be seperated out from the rest as possible candidates to fit
these new basaltic asteroids?
Graham Ensor, Nr Barwell UK
Sterling K. Webb wrote:
Hi,
The original paper on this, "Two new basaltic asteroids
in the Outer Main Belt?" by R. Duffard and F. Roig, published
in April, 2007, can be found in its entirity at:
http://arxiv.org/PS_cache/arxiv/pdf/0704/0704.0230v1.pdf
These are very small asteroids (Kumted in orbits
that mean they could never have been chips off the old Vesta (nor
apparently members of any other asteroidal "family."
They used a wide survey (the Sloan Digital Sky Survey) to find
candidates for closer examination. These two are from the first
three examined closely, which suggests the rest of the list may
well contain a lot more small basaltic bodies from as-yet-unknown
differentiated parent bodies that were totally disrupted.
Sterling K. Webb
------------------------------------------------------------------------------
----- Original Message -----
From: "Courtois Julien" <[EMAIL PROTECTED]>
To: <[email protected]>
Sent: Wednesday, August 22, 2007 10:18 AM
Subject: [meteorite-list] Strange Asteroids Baffle Scientists
From: http://www.space.com/scienceastronomy/070821_basalt_asteroid.html
Two space rocks in our solar system's outer asteroid belt might
contain mineral evidence for a new class of asteroids or long eroded
mini-worlds.
The asteroids, (7472) Kumakiri and (10537) 1991 RY16, were found to
contain basalt, a grey-black mineral that forms much of the crust on
Earth and the other inner planets.
Basalt has also been found in space rocks shed by Vesta, the third
largest object in the asteroid belt, located between the orbits of
Jupiter and Mars. The presence of basalt is evidence that an object
was once large enough to sustain internal heating.
"We need now to observe both objects in the near-infrared range to
confirm whether they have a basaltic surface," said study leader Rene
Duffard of the Institute of Astrophysics of Andalusia in Grenada,
Spain. "If they do, we will need to try to work out where they came
from and the fate of their parent objects. If they do not, we will
have to come up with a new class of asteroid."
[...]
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