[meteorite-list] Inspecting an asteroid that hit Earth

From: Michael Groetz <mpg4444_at_meteoritecentral.com>
Date: Tue, 6 Oct 2009 08:17:00 -0400
Message-ID: <ad733150910060517k225bd1d1x860674ec582e65bf_at_mail.gmail.com>

http://www.sciencenews.org/view/generic/id/48063/title/Inspecting_an_asteroid_that_hit_Earth_

Body looked like a loaf of bread, contained amino acids and may have
been blasted off a larger objectBy Ron Cowen Web edition : Monday,
October 5th, 2009

Scientists have recreated what the asteroid 2008 TC3 looked like just
before it slammed face-first into Earth on October 7, 2008. An
artist?s illustration shows, in 12-second intervals, only the
flattened part of the asteroid that faced Earth as it fell. The
horizontal line at top shows actual observations of the asteroid. P.
Scheirich, P. Jenniskens FAJARDO, Puerto Rico ? Planetary scientists
have reported a slew of new findings about the first asteroid ever
spotted before pieces of it fell to Earth. The space rock contained a
number of amino acids, had a flattened shape and appears to have been
blasted off the surface of a larger body, researchers reported October
5 at the annual meeting of the American Astronomical Society?s
Division for Planetary Sciences.

The asteroid, 2008 TC3, first came into the limelight in 2008 when
researchers spotted the body just 19 hours before it broke apart in
Earth?s atmosphere and crashed into northern Sudan. Planetary
scientists tracked the intact asteroid as it fell to the ground as
meteorites (SN: 4/25/09, p. 13).

As observed through a telescope during the last two hours of its
journey to Earth, the small asteroid appeared only as a flickering
point of light. But by analyzing the variations in brightness of the
rock as it tumbled through space, along with information culled from
fragments on the ground, Peter Scheirich of the Czech Academy of
Sciences in Ondrejov and his colleagues have now reconstructed what
the asteroid would have looked like up close. The space rock resembled
a flattened loaf of bread, Scheirich reported.

Further analysis of the shape of the asteroid, along with estimates of
the asteroid?s mass and the reflectivity of the recovered meteorites,
could reveal whether the rock is solid through and through or porous,
like a loosely held rubble pile, he adds.

The rock entered Earth?s atmosphere ?like the Apollo space capsule,
flat face forward,? says Peter Jenniskens of the SETI Institute in
Mountain View, Calif., who led an effort to recover some 300
meteorites in Sudan in October 2008.

Structures in the meteorites ? pores lined with fine-grained crystals
of a mineral called olivine ? suggest that the asteroid was blasted
off the surface of a larger rock, reported Michael Zolensky of NASA?s
Johnson Space Center in Houston. That means it should be relatively
easy to use the properties of these meteorites to understand the
properties of thousands of observed asteroids in space, which only
reveal clues about their surfaces through telescope images and
spectra, he says.

Other studies, also reported October 5, reveal that the meteorites
contain amino acids, the building blocks of proteins, that must have
come from 2008 TC3, reported Michael Callahan of NASA?s Goddard Space
Flight Center in Greenbelt, Md.

The meteorites belong to a rare type called ureilites, which contain
microscopic diamonds. ?To my knowledge this is the first report of
amino acids in any ureilite-type meteorite,? said Daniel Glavin of
NASA-Goddard, who collaborated with Callahan and other colleagues on
the analysis.

The researchers identified 18 amino acids, including
alpha-aminoisobutyric acid and isovaline. Because they are uncommon on
Earth, Glavin said, ?it is highly likely that these two amino acids
were formed in space.?

?The discovery of amino acids in [2008 TC3] provides additional
support for the idea that organic matter delivered by asteroids could
have seeded the early Earth with the raw ingredients for life,? he
noted. At the same time, the presence of the amino acids is puzzling,
Glavin added.

Evidence suggests that 2008 TC3 was heated to temperatures as high as
1,300? Celsius billions of years ago, yet amino acids are destroyed at
temperatures above 500?600?C, Glavin said. Other researchers,
including Richard Zare, Amy Morrow and Hassan Sabbah of Stanford
University in Palo Alto, Calif., reported that they had found common
components of soot known as polycyclic aromatic hydrocarbons in the
meteorites. This soot is interspersed with amino acids, Zare said.

?The big mystery now is how did these complex organic compounds
survive such high temperatures?? notes Glavin.

One possibility is that the amino acids or their precursors were
incorporated into the asteroid?s parent rock during its formation and
survived the heating and melting that would have occurred when the
parent rock was blasted into pieces. Another possibility, he notes,
is that amino acids formed inside 2008 TC3 itself much later on, after
it cooled to temperatures below 500?600?C.

To help settle these and other questions, Jenniskens plans to return
to Sudan this December to pick up more specimens.
Received on Tue 06 Oct 2009 08:17:00 AM PDT