[meteorite-list] Posts yesterday related to possible Peruvian bolide from 2/2/2004

From: Matson, Robert <ROBERT.D.MATSON_at_meteoritecentral.com>
Date: Fri, 2 Mar 2007 14:50:09 -0800
Message-ID: <A8044CCD89B24B458AE36254DCA2BD070321B5EB_at_0005-its-exmp01.us.saic.com>

Hi All,

Now that I've figured out the problem, let me re-post a number of
messages
that were exchanged between myself and Randall Gregory yesterday
regarding
the possible Peruvian bolide from 2/2/2004. (Apologies in advance when
those html messages show up in another day or two.) Here was the first
that was cc'ed to the list from yesterday by Randall (which has my
message
below it that he was replying to):

- - - -
3/1/2007 7:48am

Rob,
 
Do you really believe that a dust-devil the size of a F3* tornado,
eyewitnesses to a streak leaving a trail, and a 4.0 earthquake event
just happened to occur simultaneously at exactly 12:00 is just a
coincidence? Isn't that stretching Occam's Razor just a tweak?
 
You probably know about this software program to estimate impact
characteristics aptly named Earth Impact Effects Program.
 
http://www.lpl.arizona.edu/impacteffects/
 
It give a rough approximation to the expected effects of a large mass
impacting the earth's surface. I tried adjusting the variables to
approximate a 4.0 seismo. The results are at the lower levels of impact.
This program indicated that there probably would not have been
impactites created but would have produced small cratering. It also
indicates that meteorites would have a much higher velocity than you
stated. You indicated a couple of hundred meters per second. The actual
velocity I believe would be closer to 15 kilometers/sec. Would that be
sufficient to create superheated air? I believe there would be
atmospheric heating of an object this size and the program
substiantiates it.
 
This of course is all debatible. We both know scientists are in a
constant state of debate.:)
 
Randall

 
* Please don't get picky on me. I know F3 relates to wind velocity and
damage on the Fujita scale. Just using this for relative size
comparison. OK? ;)

"Matson, Robert" <ROBERT.D.MATSON at saic.com> wrote:
Hi Randall,
 
> Thank you for your insightful post. Yes, that may be true for many
> sightings. But I want to ask you a big question. How many of the
> sightings you mentioned occurred during the day? How many had a
> mountain range in the background? This happened at noon.
 
Well, most observed bright meteors naturally occur at night when they
are more apt to be noticed. From a meteorite survival standpoint, late
afternoon to early evening is best since these meteors will be slower
and thus the deceleration will be less severe on the meteoroid body.
 
> But this was unique because the "polvera" or columnar dust cloud was
> located just before a set of mountains giving a quite accurate
location
> to the indicated impact.
 
> The polvera rose thousands of meters in the air and was visible to the
> people in the city of Aplao. What was really interesting was when I
> interview the witnesses, they all indicated a column, rather than a
> mushroom cloud. This is my theory, but please remember that it's just
> a theory. I believe that the meteorite created a column of
super-heated
> and expanded air. The impact dust/debris followed the path of least
> resistance and remained in columnar form. My theory.

Unfortunately, what you are describing is not consistent with a modest
bolide fall. Meteoroids lose their cosmic velocity well above the
surface
of the earth, and then freefall at (much lower) terminal velocity for
the
final 2-4 minutes before hitting the ground. During that time, the
meteoroid (or meteoroids if there has been a break-up) have no effect on
the atmosphere. The atmosphere is not heated by the passage rocks in
freefall, and the eventual ground impact velocity depends solely on the
individual masses of the meteorites produced and their bulk densities.
Typical impact velocities are on the order of a couple hundred meters
per second.
 
The only place where "superheated" air can occur is when the bolide
still has appreciable cosmic velocity, and this only occurs when its
altitude is still at least 15 km (and more often not below 20 km). To
have superheated
air all the way down to the ground implies cosmic velocity all the way
down
to the ground. If this happens, you aren't talking a kiloton impact,
you're
talking many megatons (like Tunguska).
 
Seems to me a more likely explanation for a daytime columnar cloud is
just a dust-devil.
 
> Peru is a earthquake prone country and has an extensive seismic net.
> They work closely with the Japanese and have state-of-the-art
equipment.
> I have seismic waveforms data captured from six stations on the net,
if
> you're interested.
 
Well, if you've got the coordinates and altitudes of each of the
stations,
and the times of the seismic (or in the case of a bolide, acoustic)
waveforms, you have all you need to triangulate a burst location. If it
was a bolide undergoing a terminal burst, that will be immediately
apparent from the seismometers, since the delays between individual
stations will be much larger than for an earthquake or ground impact.
 
--Rob
Received on Fri 02 Mar 2007 05:50:09 PM PST