[meteorite-list] GRAND CANYON METEOR

From: Matson, Robert <ROBERT.D.MATSON_at_meteoritecentral.com>
Date: Thu Apr 22 09:52:18 2004
Message-ID: <AF564D2B9D91D411B9FE00508BF1C86901B4E2E2_at_US-Torrance.mail.saic.com>

Hi Stephen,

Thank you for sharing with the list your account of a bright meteor
over Grand Canyon NP. For clarification and additional analysis,
I have a few questions for you.

> On the evening of Wednesday, August 14, appx. 9:30-9:45pm Arizona time,
> my son and I were on a nite "star" hike with an NPS ranger at Bright Angel
> Point on Grand Canyon's North Rim. A huge meteor raced across much of the
> sky, running south to north. It lasted as long as 6-8 seconds, was
> bluish-white in color, and was extremely bright.

When you say it lasted 6-8 seconds, was your view blocked from seeing
the end (e.g. behind trees) or did it just fade out? Did you notice
any fragmentation? How high up in the sky was the meteor when you
first spotted it, and was the track to the east of you, west of you,
or dead overhead as it traveled south to north?

> About 10 seconds after it disappeared, there came a loud boom that
> eventually echoed down through the Canyon.

Okay, this is probably the most important piece of information, so
I'd like to pin you down on the uncertainty if I can. Can you give
me a range of time delays that bound the uncertainty? For example,
if you're sure the sound came at least 10 seconds later, but certainly
no more than 30 seconds later, this would be helpful. If you can
narrow the uncertainty to a smaller range (e.g. "it was between 10
and 12 seconds later") great, but pick a range that you're confident
in. The reason I ask is because a 10-second delay between seeing
a meteor and hearing a sonic boom from it is simply too short. Even
if the time of the meteor's closest approach (highest elevation
angle) was close to the beginning of when you spotted it, that
would mean a delay of about 18 (8+10) seconds. This would correspond
to a meteor altitude of only about 5.5 km, which is way too low:
about a quarter of the lowest altitude you could reasonably expect.
Is there any chance it was thunder, or were your skies completely
clear?

> I was thinking that it was unlikely that it hit the Earth, and that
> the sound was just a sonic boom, but hoping that it had made contact
> somewhere just north of us. I have seen many "shooting stars", and
> many good ones, but this completely blew everything else away.

The probability that the meteoroid produced a meteorite depends
a lot on how bright it was -- was it bright enough to cast
shadows? Was it dimmer or brighter than a full moon?

> A traveler came into the ranger's office while we were speaking
> about this, and he said that he'd been staying at a lodge just up
> the road about 20 miles, and saw it as well. He said that they
> could see debris "fly up" when it landed.

I wouldn't place much stock in this traveler's description -- it
is either an embellishment of what he saw, or an inadvertent
association of two unrelated events -- the meteor in the sky, and
something else much closer to him.

> Does anybody: A. Have any information on this occurrence?

Your report was the first I heard of it, but I'll now keep an eye
out for others.

> B. Have any suggestions on where I can/should "report" this?

FIDAC. Here's a link:

http://www.imo.net/fireball/index.html

Click on the "Hints" link for some instructions for filling out the
online fireball report form.

Best,
Rob
Received on Mon 19 Aug 2002 09:10:48 PM PDT