[meteorite-list] Oxygen Isotope Ratios was Lunar velocities...

From: meteorites_at_space.com <meteorites_at_meteoritecentral.com>
Date: Thu Apr 22 09:44:44 2004
Message-ID: <20010331205055.29534.cpmta_at_c000.snv.cp.net>

On Sat, 31 March 2001, Kelly Webb wrote:

> Dear Elton, Darryl, Robert, and List,
> Oxygen isotope ratios are indicative of the composition of the
> original material from which a body condensed and accreted. The values
> for material from the Earth and the Moon, on a log (or sigma) graph,
> occupy a little common island centered on the terrestrial fractionation
> line. Oxygen isotope ratios cannot distinguish between lunar and
> terrestrial materials.
> EH and EL meteorites are also on the terrestrial fractionation line
> in an island that overlaps the Earth/Moon island. SNC's have their own
> island of values just above that line; achondrites and stoney-irons just
> below that line. The H, L, and LL chondrites each have an island of
> values further above the terrestrial line. Carbonaceous chondrites have
> a fractionation line all their own, with a different slope entirely.
> All this "proves" is that the Earth and the Moon condensed and
> accreted from the same region of the forming solar system. It also
> strongly implies that the original material of the inner (at least, and
> probably outer) solar system was not well-mixed, was strongly zoned by
> composition, and that the inner system bodies were rapidly assembled
> from fairly narrow accretion zones.
> If, as is currently believed, the Moon was formed in a low-speed
> impact (<5000 m/sec) with the Earth, the two bodies would have had to
> have similar orbits before collision (otherwise the collision wouldn't
> have been so low-speed). This would fit the scenario above.
> Oxygen ratios identify lunar achrondrites because their values are
> not "meteoritic." The values for tektites are earth/moon-like, but fall
> in a very narrow range (+/- 4%) of values, a much smaller range than
> terrestrial surface rocks, for example. This points to a) an unique
> source material, or b) formation by an unique process. Of course, we
> knew that already. We just don't know the what, where, when, how, and
> all those other little details that make life interesting.
> The big picture: this is all based on data from physical samples
> that a) we have in hand and b) whose origin is known. When you consider
> that, you realize that we're operating in near darkness here. Make a
> list of all the solar system bodies and then check off whether or not we
> have a sample of them. Mercury, no. Venus, no. Earth, yes (duh). Moon,
> yes. Near Earth asteroids (Atens, Apollos, Amors), no (?). Mars, yes
> (but not enough). Comets, no. Some asteroids (Vesta, M, C, E, ?), yes.
> Other classes of asteroids, no (uncertain). From here on out, it's all
> no, no, no. It's like being given ten random words from a full page of
> text and being asked to reconstruct that text.
> Sterling K. Webb
> --------------------------------------------
> "E.L. Jones" wrote:

The unique enstitite meteorite ABEE has certain properties that some interpret as possibly coming from the reaches of the inner Solar System.

Mercury ?

At least that is what Russel Kempton... and others seem to say.


Steve Schoner, AMS

> >> I ask again , are the oxygen isotope ratios (O16-O17
> >> -O18) in tektite glass indicitive of a lunar origin or an
> >> Earthly origin? If this analysis hasn't been done ..Why
> >> Not? It is good enough for evidence of lunar origin in
> >> meteorites-- why not tektites?
> >>
> >> Regards,
> >> Elton
> >>
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Received on Sat 31 Mar 2001 03:50:55 PM PST

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