[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
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.
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
> Meteorite-list mailing list
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Received on Sat 31 Mar 2001 03:50:55 PM PST