[meteorite-list] meteorite question-direction of fall

From: E.L. Jones <jonee_at_meteoritecentral.com>
Date: Thu Apr 22 10:25:40 2004
Message-ID: <3EC1C5AF.7080403_at_epix.net>

The answer is maybe, sometimes, and yes, but not always precisely....

Theoretically and historically, the "direction of fall" can be
determined to within a few degrees and the "angle of fall" might be
estimated. To my knowledge, we have had very few strewn fields mapped
since the advent of desktop computers, GPS Units, and sophisticated
statistical packages. So what I am about to say may be overcome by
events.

In the old days.... When a strewn field was mapped and mathematically
converted to a "distribution ellipse"* an apparent long axis and
lateral axis would become apparent. Physics dictate that the larger
fragments will lie at the far end of the strewn field(usually). So back
tracking the long axis away from the larger fragments indicates the
direction from which the fall arrived. The greater the angle of fall,
the less reliable the direction may be ascertained.

A relatively long ellipse indicates a more shallow angle of fall. The
more narrow the ellipse, the more accurate the direction will be
estimated. If the fall was from a high angle, the ellipse will tend to
be more circular(i.e as long as wide) and the rule about heaviest
fragments at the long axis of the strewn field may not always apply.

The reason that larger masses tend to fall long in a shallow angle of
falls, is that they are have more momentum to dissipate. Air resistance
has longer to influence the flight path of all fragments however,
smaller masses are slowed more quickly by the atmosphere. The lower the
angle of fall the longer the time spent in increasingly thickening air.

In a high-angle fall, the air resistance doesn't have the flight time to
aerodynamically sort the sizes and they tend to land largely unsorted
and the ellipse is more circular.

If there are several large fragmenting bodies or, an extended, episodic
fragmentation (.i.e. Peekskill where over 70 fragments were counted to
have shed over 200+ miles), the ellipse might map to some exotic shape
but still might retain some useful data as to direction of fall.
I am unaware of comparative strewn field studies which I can pass along.
  Maybe someone else has an example in their database.

*More about the use of a distribution ellipse: Early on, upon recovery
of several fragments an ellipse is computed to give searchers an area on
the ground to concentrate recovery efforts. It is refined more masses
are recovered until the field is searched out. As I recall, depending on
the statistical treatment, an ellipse will give an area where 95% of the
fragments should be found within.

Regards,
Elton



WAHLPERRY_at_aol.com wrote:
> Hi List,
>
> I was discussing this with a friend and hope one of you may be able to
> answer this. Is it possible to tell what direction a meteorite came from
> by the way the fragments are found in relationship to the larger piece
> of the same stone?
>
> Thanks,
>
> Sonny Clary
Received on Wed 14 May 2003 12:27:27 AM PDT