[meteorite-list] FW: Rocks from Space Picture of the Day -May 8, 2010

From: Rob Matson <mojave_meteorites_at_meteoritecentral.com>
Date: Sun, 9 May 2010 00:19:37 -0700
Message-ID: <GOEDJOCBMMEHLEFDHGMMEEDMEDAA.mojave_meteorites_at_cox.net>

Hi All,

Short opinion: manmade.

Reasoning: the inability to produce such a form purely through
atmospheric ablation. Just to remind everyone, all of the
so-called Franconia irons are nothing more than chondritic
iron that has separated from an H-chondrite fall -- either
during flight, or by terrestrial weathering processes on the
ground. Thus it has always bothered me that these irons were
given a separate meteorite name from the ubiquitous H-chondrites
at Franconia from which they derive. If my information is
outdated on this subject, someone please let me know. But many
(most?) of the people I know who have hunted Franconia and
found these irons do not pretend that they are from a separate
iron fall -- they all accept that the iron nuggets were
spalled from an H-chondrite.

So, getting back to Larry's unusual, tiny iron find. If this
iron did not start at the top of the atmospere as a very tiny
piece of iron, there would be no way to ablate it, let alone
punch a hole through it. Since the Franconia irons were once
part of a massive chondritic meteoroid, there was no opportunity
for these irons to experience independent, high altitude, high
velocity ablation. Their ablation history wouldn't have started
until the main H-chondrite body had fragmented on a gigantic
scale (e.g. terminal burst), which of course would have
occurred at comparatively low altitude.

On a final note, the H-chondrite fall at Franconia was not
a recent one. While this part of NW Arizona receives little
seasonal rainfall, I don't imagine that a 0.1-gram piece of
iron could survive more than a century. But a manmade piece
of iron, dropped there in the last 50 years, might possibly
survive terrestrial weathering.

I would love nothing more than for Larry's find to have an
extraterrestrial origin; but the physics and history of finds
at Franconia argue strongly against it.

Best wishes,
Rob
Received on Sun 09 May 2010 03:19:37 AM PDT