[meteorite-list] Fwd: (meteorobs) 2012/02/01 TX Fireball

From: Mike Hankey <mike.hankey_at_meteoritecentral.com>
Date: Wed, 8 Feb 2012 21:47:03 -0500
Message-ID: <CAJak_qU_VEGt2XHZ=YvVkrrZQmO7CaCF6ae4sQ02bg79hqcfHg_at_mail.gmail.com>

---------- Forwarded message ----------
From: Bill Cooke <cookewj at comcast.net>
Date: Wed, Feb 8, 2012 at 9:42 PM
Subject: Re: (meteorobs) 2012/02/01 TX Fireball
To: Meteor science and meteor observing <meteorobs at meteorobs.org>


We have spent the last few days analyzing the Sandia camera videos
kindly provided by James Beauchamp and Kevin Palivec (also thanks to
Esko Lyytinen for his insight and comments). These have enabled us to
determine a decent trajectory for the meteor; unfortunately the meteor
entered at a shallow angle and its path/duration was so long (18.5
seconds) that the linear approximation used in the trajectory codes
(MILIG, courtesy of J. Borovicka, and SMETS) is not valid, resulting
in a possible error of several (~5) kilometers in the final position.
Consequently, we did not attempt the dark flight calculations needed
to determine the impact zone, as an error of 5 kilometers in position
at 30-40 km altitude would translate to over a hundred square
kilometers of uncertainty in the meteorite fall area. I can say that a
solution using the first hundred frames of video (meteor is above 65
km altitude) yields a trajectory consistent with the Edgewood doppler
returns; all other solutions
?put the meteor path about 20 km to the north of the radar signature.

Here are the beginning and end coordinates of the meteor, based on a
solution involving all 976 points (frames) from the 3 videos:

Meteor beginning point: 99.176 W, 32.108 N at an altitude of 92 km
Meteor end point: 96.357 W, 32.745 N at an altitude of 43 km

Mean residuals in trajectory fit (residuals show systematic trends due
to breakdown of linear path approximation)

Coleman: -0.045 km vertical, 0.703 km horizontal
Hawley: -1.889 km vertical, -1.711 km horizontal
OKC: +1.302 km vertical, -0.123 km horizontal

Again, the end point is NOT the impact location; it represents the
meteor position in the last frame in the OKC all sky camera video.

Average speed is 16.3 +/- 1.4 km/s
Initial meteor speed: ~18 +/- 1 km/s
End meteor speed: 9.8 +/- 4 km/s

I am confident this meteor produced meteorites. Seen by our camera way
over in New Mexico, it was very bright, with peak absolute magnitude
around -14 (lower limit). Mass estimates from the light curve range
from about 20 kg to just over a metric ton (1017 kg), depending on
whose equations/technique you use. I consider a few hundred kg likely,
but would find it hard to argue against the metric ton figure. How
much mass made it to the ground is anyone's guess, but be assured that
this was a BIG rock that blazed across the Texas sky.

The gory details are in this pdf file:
http://www.billcooke.org/events/20120202_0157.pdf
The complete meteor trajectory (text file) is here:
http://www.billcooke.org/events/smets.txt

Reference for MILIG: Borovicka J.: The comparison of two methods of
determining meteor trajectories
from photographs. Bull. Astron. Instit. Czechoslovakia, 41, 391-396 (1990)

Regards,
Bill Cooke
NASA Meteoroid Environment Office
Marshall Space Flight Center
Email:william.j.cooke at nasa.gov
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Received on Wed 08 Feb 2012 09:47:03 PM PST