[meteorite-list] HUGE Meteor Sighting in Cottonwood AZ - Stats from fall

From: Steinar Midtskogen <steinar_at_meteoritecentral.com>
Date: Mon, 14 Apr 2014 21:20:33 +0200
Message-ID: <87tx9viupq.fsf_at_latinitas.org>

Chris Peterson <clp at alumni.caltech.edu> writes:

> The majority that produce _falls_, yes, but not _finds_, I think. That
> is, your typical find (either a single individual or several pieces)
> probably didn't come from a spectacular meteor event. Of course, finds
> in large strewn fields are a different matter.

Yes. A meteor travelling at 11 km/s only has a 1/4 of the energy of
an equally sized meteor travelling at 22 km/s.

The fall of the two most recent meteorite finds in Norway can be
dated, but none had reports of sound. Most of these meteorite
dropping fireballs are not bright enough to be detected because of
clouds or daylight, and anything audible can easily be mistaken for
thunder or human activity anyway.

> Atmospheric entry models demonstrate that it's not difficult for a
> small body to drop a few rocks on the ground without ever depositing
> the sort of energy into the atmosphere we associate with bright
> fireballs lasting several seconds and producing audible acoustics at
> ground level.

The most recent find in Norway, a 4,5 kg chondrite, seems to have come
from this innocent looking fireball, seen from about 200 km:

  http://norskmeteornettverk.no/bilder/2013/ildkule-20120203.mp4

The brightness normalised to 100 km distance seems to be around -10,
and it was visible for 3.3 seconds, not very impressive. It was
photographed by two cameras and the bearings match very well (but
there is a ?25 km or so uncertainty, so there is a slight possibility
that the fireball is unrelated). The speed was 13 km/s, angle of
incidence 57 degrees, and it burned out between 25 and 30 km altitude.
I originally dismissed it as a somewhat unlikely meteorite candidate,
but when a meteorite was found by chance 16 months later, I'm much
less sure and I rather lean towards that it did produce this
meteorite.

-- 
Steinar

Received on Mon 14 Apr 2014 03:20:33 PM PDT