[meteorite-list] Strange Asteroids Baffle Scientists

From: ensoramanda <ensoramanda_at_meteoritecentral.com>
Date: Thu, 23 Aug 2007 01:20:15 +0100
Message-ID: <46CCD2BF.6020308_at_ntlworld.com>

Thanks Stirling,

Interesting relationships to the iron meteorites. I had naver considered
that they indicated so many large differentited bodies.

Is it not possible that one body may have an iron core that has a range
of nickel iron mixes thus producing several classes of iron meteorites
from the same source?. Surely a large core would have areas that cooled
at different rates producing fine and coarse irons with different
chemical makeups.

Graham

Sterling K. Webb wrote:

>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" <ensoramanda at ntlworld.com>
>To: "Sterling K. Webb" <sterling_k_webb at sbcglobal.net>;
><Meteorite-list at meteoritecentral.com>
>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" <ivlianvs at gmail.com>
>>To: <Meteorite-list at meteoritecentral.com>
>>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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Received on Wed 22 Aug 2007 08:20:15 PM PDT