[meteorite-list] Carancas in the news PLUS GRA 06128/9

Wed Feb 27 17:09:35 EST 2008

Hi,

    For those interested in the odd Antarctic meteorites
mentioned in this MSNBC story, here's the paper on them:
http://www.lpi.usra.edu/meetings/lpsc2008/pdf/2215.pdf

    "GRA 06128 & 06129 are paired achondrites,
with unique mineral proportions (75% oligoclase),
mineral compositions, and oxygen isotope ratios. They
appear to represent alkalic igneous rock from a hitherto
unsampled differentiated parent body, modified significantly
by thermal and shock metamorphism."

    "The meteorites are slab-shaped gray rocks with
partial fusion crusts of shiny black glass. They consist
of massive rock (grain sizes ~500 micrometers)
gradational and interlayered with strongly foliated easily
split rock (grain sizes ~ 50 micrometers). The foliation is
defined by parallel fractures; no lineations were seen.
The meteorites are extensively rusted, and emit a
sulfurous odor on crushing."

    They sound a lot like Carancas, don't they?
Slabby gray rocks with shiny black glassy crusts,
troilite, sulfurous smell, heavily shocked... But
there are no chondrules in GRA and no oligoclase
in Carancas! (GRA is 75% oligoclase.)

    They are definitely weird puppies, and you know
that most weird puppies have an interesting story to
tell if you can get'em to talk. Despite the tippie-toeing
around of the circumspect authors of the paper, there
is only one class of object they could have come from:
a planet, er, OK, 'cuse me, a differentiated body.

Theory says there can be small differentiated bodies,
but we don't KNOW of any, so, a source as big or
bigger than Vesta, you know, like Venus... or Mercury.
Of course, they don't fit our expectations for those locales;
why should they? It's not like we actually knew what
Venus or Mercury's surface is like.

    There's a lot of work to be done on these two rocks:
"Additional studies in progress include reflectance spectroscopy,
bulk chemistry, Ar isotope analyses and Ar-Ar dating, and radiogenic
isotope analyses in the systems Rb-Sr, Sm-Nd, Re-Os, and Lu-Hf."
They haven't even done thin sections yet. Unknown
achondrite? It'd make me hustle a little...

    If it were from Venus (for example), the Ar isotopes
ratios would pretty much scream it out...

Sterling K. Webb
-------------------------------------------------------------------------
----- Original Message ----- 
From: "Darren Garrison" <cynapse at charter.net>
To: <meteorite-list at meteoritecentral.com>
Sent: Tuesday, February 26, 2008 10:24 AM
Subject: [meteorite-list] Carancas in the news

Messages aren't going through the list, so I'm sending this to you directly.

http://cosmiclog.msnbc.msn.com/archive/2008/02/25/701427.aspx

Meteorites spark mysteries Posted: Monday, February 25, 2008 8:20 PM by Alan
Boyle

Five months after a meteorite made an international splash in Peru, experts 
are
suggesting explanations for some of the space rock's effects - for example, 
the
sickening odor villagers smelled at the crash site, and the bubbles that 
were
seen emanating from the water-filled crater left behind. But a study due to 
be
presented next month also raises fundamental questions about the event. In 
fact,
an international research team declares that the impact "should not have
happened" at all.

Yet another study sets forth a mystery surrounding two other meteorites 
found in
Antarctica a couple of years ago. The rocks don't match any other class of
meteorite - so where did they come from?

The two studies are among hundreds submitted for the annual Lunar and 
Planetary
Science Conference, scheduled March 10-14 in League City, Texas. The 
conference
offers the cream of the crop in planetary science - focusing on topics 
ranging
from the solar wind, to Mercury and Mars, to the icy dwarfs on the solar
system's edge.

The Peruvian meteorite impact comes in for a fresh round of scientific 
scrutiny
in a study submitted by researchers from Brown University and institutes in 
Peru
and Uruguay. Just after the impact was reported, some scientists doubted 
whether
a meteorite was actually responsible for the crater - but subsequent 
analysis
proved that a stony space rock was involved (as opposed to a denser iron
meteorite).

Scientists previously thought that stony meteorites on the scale of the one 
that
hit Peru would break apart into little pieces before they hit the ground. 
The
fact that this one survived to create a 40-foot-wide crater threw the
researchers what they called a "hypervelocity curveball." They said the 
standard
model used to estimate the effects of stony meteorites will need to be 
revised
as a result.

The study does propose two possible explanations for the reports of "boiling
water" seen within the crater: The bubbles could have come from the 
compressed
air that surrounded the meteorite as it blasted into the wet earth - or it 
could
have been caused by clumps of clay that dissolved and frothed as they fell 
into
the crater.

"These two processes may have been responsible for local reports of water
bubbling up from the floor soon after impact," the researchers wrote. "While
there would have been heat generated at impact, it is unlikely that this 
could
have sustained bubbling an hour later."

Meteorite hunter Michael Farmer, who visited the site last year soon after 
the
impact, has said the sickening odor that villagers said emanated from the 
crater
was most likely caused by sulfurous compounds such as triolite interacting 
with
the ground water - and there's nothing in the latest study that contradicts 
that
suggestion.

The Peruvian meteorite may be in for another shot at fame: Just last week,
Living in Peru reported that Japanese investors are interested in building a
space museum near the impact site, and that National Geographic is planning 
a
documentary about the meteorite.

Now to the other space-rock study: Meteorite hunters from the Lunar and
Planetary Institute and NASA's Johnson Space Center reported finding a pair 
of
specimens in 2006 in Antarctica's Graves Nunataks area.

"These meteorites are not obviously like any other meteorites, so their 
origin
is unclear," the Lunar and Planetary Institute said in its media advisory. 
"The
mineralogy and chemical composition of these meteorites are so unusual that
scientists have been struggling to find the right term to describe them.
Numerous parent bodies have been proposed. Could they have come from the 
moon?
>From Venus? Scientists are currently debating these issues."

The researchers behind the study say they're not finished with their 
analysis of
the rocks, and more findings may emerge at next month's conference. So stay
tuned as the meteorite tales and other mysteries are fully brought to light.
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