[meteorite-list] Carancas in the pit?

From: Rob Matson <mojave_meteorites_at_meteoritecentral.com>
Date: Wed, 17 Oct 2007 23:42:01 -0700
Message-ID: <GOEDJOCBMMEHLEFDHGMMEEDODGAA.mojave_meteorites_at_cox.net>

Hi Sterling,

I'm packing for Hawai'i (vacation, yeah!), so this'll be the
last post from me for a while, but didn't want you to think I
had abandoned the discussion...

> I wasn't making a comparison between Carancas Crater and
> Meteor Crater and invoking any similarity -- vastly different
> events. But I was putting the case of D. M. Barringer
> forward as an example of the strength of the psychological
> attraction to the idea of the survival of the meteorite body.

Ahh, understood: your comparison was strictly on an historical,
psychological level w.r.t. post impact expectations.

> There is no evidence of a gentle impact in Carancas, and
> plenty of evidence of an energetic thermal event.

I would say that the "evidence" for a thermal event is largely
anecdotal at this point:

> 1. The odors, fumes, noxious vapors, etc. reported by all the
> witnesses (who may well have reacted hysterically to them) are
> easily explained by the vaporization of the troilite (5% of the
> stone), an event that requires temperatures in excess of 700
> degrees K.

Physical pulverization (of a fraction of the bolide) is also an
adequate explanation. The evidence for fumes/vaporization is
physiological and/or psychological, and thus not 100% reliable.
I should think that the meteorite fragments themselves would
offer some tangible evidence, one way or the other, for how
energetic the impact was, and what sort of thermal effects
occurred.

> 2. The various witness reports: a man knocked over at 300 meters,
> an event that requires a high level of overpressure;

Here again, the evidence is based on witness testimony, and thus
potentially subject to a bit of exaggeration in the retelling.
Not saying that the witness *is* exaggerating, just that there
is no way to know.

> ... windows broken in Desaguadero, 10,800 meters away...

A sonic boom will do that without requiring a thermal impact event.

> ... two domestic animals, closer than 300 meters, killed by the
> blast...

I've seen no evidence to support this claim.

> 3. The extreme weakness of the stone (you can break it in your
> hand using only human muscles) makes the survival of "pieces
> in the pit" very unlikely in an event with the above character-
> istics.

The counterargument is that if the stone was so fragile, how did
any of it survive in solid form? It would be one thing if spalled
fragments were found relatively distant from the impact site, but
the fragments recovered were found in the pit itself. How did
they avoid pulverization to powder?

> Rob, the absence of any evidence of fragmentation puzzles
> me as much as it seems to you. How could a big object of
> such friable material NOT drop numerous secondaries?

Seems to me it must have.

> There should be some evidence of a "shower," a kind of miniature
> Holbrook over Peru, but there isn't. This stuff should have
> disintegrated in flight.

And yet it didn't, which has me scratching my head. The initial
entry velocity had to be over 15 km/sec. In a matter of less than
10 seconds (for a relatively steep entry angle), that velocity had
to plunge by more than 12 km/sec before impact, implying an ~average~
deceleration of more than 120 Gs. (The actual peak deceleration
would have been quite a bit greater since atmospheric pressure
rises exponentially as the bolide penetrates the atmosphere.)
That's the main reason I'm skeptical that nothing significant remains
in the pit: it wasn't an air burst. Can the ground achieve what
the atmosphere could not? --Rob
Received on Thu 18 Oct 2007 02:42:01 AM PDT