[meteorite-list] FW: Lunar origin of tektites

[Matson, Robert]

Resending this message, which as usual did not post to the IMCA
message group.  I'm CCing Meteorite Central in case it fails to
show up at IMCA a second time.  --Rob

-----Original Message-----
From: Matson, Robert 
Sent: Thursday, March 24, 2005 11:47 PM
To: 'meteoritecollectorsassociation at yahoogroups.com '
Subject: Lunar origin of tektites


Hi Doug and List,

Some of you (most of you?) are probably already aware of my position
on the lunar origin of tektites, but for those who don't I'll throw
in my two cents from the dynamics standpoint.  Short answer:  no dice.

Years ago I didn't have an opinion or a vested interest one way or
the other -- I was honestly curious if the lunar origin could be
dynamically supported.  So I modeled it and ran millions of Monte
Carlo simulations to see where either volcanic or lunar impact
ejecta material would end up.  The answer is:  if an intercept is
possible, it rains down on more than a hemisphere of the earth (as
well as significant portions either back on the Moon or in solar
orbit).  There is no natural way to favor a geographic region on
the earth when the Keplerian trajectory origin is on the Moon.  The
angular tolerances are just too tight.

Lunar volcanism is an even more restrictive case since it requires
the initial velocity vector to not only deviate significantly from
the local lunar zenith direction, but in exactly the correct direction
for an earth intercept.  Anything other than a direct intercept
path on a pencil-thin beam results in tektites scattered over more
than a hemisphere.

> I am eating up Norm's comment that some bona fide Indochinite
> researcher out there (an endangered species), is mulling over the
> possibility of Lunar origin for Indochinites as this is EXACTLY
> what I was implying in my last post about all glass not being
> equal and a certain tektite not-so-hypothetically being proven
> to be of Lunar origin.

Not one researcher has offered a scenario by which a lunar impact
results in tektites scattered on the earth in not only a limited
geographic area, but with a non-elliptical pattern.  The earth is
a tiny enough target from the Moon's distance; to generate the
limited (and non-elliptical) distribution of tektite finds requires
a reasonable dynamic mechanism.  None has been offered that can
be mathematically reproduced.

Norm wrote:

> ... Dean Chapman's  1971 article  in the Journal of Geophysical
> Research ... looked  at australasian  distribution patterns and
> demonstrated that they are  consistent with  theoretical
> distributions of ejecta from a particular  ray of crater  Tycho
> is more than a statement of  opinion.

I studied the special case of Tycho precisely because of Chapman's
paper.  Ignoring for the moment that the Tycho crater is believed
to be about 100 million years old, I found the results irreproduce-
able.  Would love to see Chapman's source code to see what assumptions
he made, but based on the lunar latitude and longitude of Tycho,
and the azimuth angle of the Rosse ray, I do not come up with a
direct intercept solution for the earth, no matter what one chooses
for the local lunar elevation angle and initial velocity of the
tektite precursor fragments.

--Rob