[meteorite-list] More Asteroids Could Have Made Life's Ingredients

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu, 20 Jan 2011 17:48:47 -0800 (PST)
Message-ID: <201101210148.p0L1mlvW021225_at_zagami.jpl.nasa.gov>

http://www.nasa.gov/topics/solarsystem/features/left_hand_aminoacids.html

More Asteroids Could Have Made Life's Ingredients
Goddard Release No. 10-006

Nancy Neal-Jones
NASA's Goddard Space Flight Center
Greenbelt, Md.
301-286-0039
Nancy.N.Jones at nasa.gov

Bill Steigerwald
NASA's Goddard Space Flight Center
Greenbelt, Md.
301-286-5017
william.a.steigerwald at nasa.gov

01.18.11
 
A wider range of asteroids were capable of creating the kind of amino
acids used by life on Earth, according to new NASA research.

Amino acids are used to build proteins, which are used by life to make
structures like hair and nails, and to speed up or regulate chemical
reactions. Amino acids come in two varieties that are mirror images of
each other, like your hands. Life on Earth uses the left-handed kind
exclusively. Since life based on right-handed amino acids would
presumably work fine, scientists are trying to find out why Earth-based
life favored left-handed amino acids.

In March, 2009, researchers at NASA's Goddard Space Flight Center in
Greenbelt, Md., reported the discovery of an excess of the left-handed
form of the amino acid isovaline in samples of meteorites that came from
carbon-rich asteroids. This suggests that perhaps left-handed life got
its start in space, where conditions in asteroids favored the creation
of left-handed amino acids. Meteorite impacts could have supplied this
material, enriched in left-handed molecules, to Earth. The bias toward
left-handedness would have been perpetuated as this material was
incorporated into emerging life.

In the new research, the team reports finding excess left-handed
isovaline (L-isovaline) in a much wider variety of carbon-rich
meteorites. "This tells us our initial discovery wasn't a fluke; that
there really was something going on in the asteroids where these
meteorites came from that favors the creation of left-handed amino
acids," says Dr. Daniel Glavin of NASA Goddard. Glavin is lead author of
a paper about this research published online in Meteoritics and
Planetary Science January 17.

"This research builds on over a decade of work on excesses of
left-handed isovaline in carbon-rich meteorites," said Dr. Jason Dworkin
of NASA Goddard, a co-author on the paper.

"Initially, John Cronin and Sandra Pizzarello of Arizona State
University showed a small but significant excess of L-isovaline in two
CM2 meteorites. Last year we showed that L-isovaline excesses appear to
track with the history of hot water on the asteroid from which the
meteorites came. In this work we have studied some exceptionally rare
meteorites which witnessed large amounts of water on the asteroid. We
were gratified that the meteorites in this study corroborate our
hypothesis," explained Dworkin.

L-isovaline excesses in these additional water-altered type 1 meteorites
(i.e. CM1 and CR1) suggest that extra left-handed amino acids in
water-altered meteorites are much more common than previously thought,
according to Glavin. Now the question is what process creates extra
left-handed amino acids. There are several options, and it will take
more research to identify the specific reaction, according to the team.

However, "liquid water seems to be the key," notes Glavin. "We can tell
how much these asteroids were altered by liquid water by analyzing the
minerals their meteorites contain. The more these asteroids were
altered, the greater the excess L-isovaline we found. This indicates
some process involving liquid water favors the creation of left-handed
amino acids."

Another clue comes from the total amount of isovaline found in each
meteorite. "In the meteorites with the largest left-handed excess, we
find about 1,000 times less isovaline than in meteorites with a small or
non-detectable left-handed excess. This tells us that to get the excess,
you need to use up or destroy the amino acid, so the process is a
double-edged sword," says Glavin.

Whatever it may be, the water-alteration process only amplifies a small
existing left-handed excess, it does not create the bias, according to
Glavin. Something in the pre-solar nebula (a vast cloud of gas and dust
from which our solar system, and probably many others, were born)
created a small initial bias toward L-isovaline and presumably many
other left-handed amino acids as well.

One possibility is radiation. Space is filled with objects like massive
stars, neutron stars, and black holes, just to name a few, that produce
many kinds of radiation. It's possible that the radiation encountered by
our solar system in its youth made left-handed amino acids slightly more
likely to be created, or right-handed amino acids a bit more likely to
be destroyed, according to Glavin.

It's also possible that other young solar systems encountered different
radiation that favored right-handed amino acids. If life emerged in one
of these solar systems, perhaps the bias toward right-handed amino acids
would be built in just as it may have been for left-handed amino acids
here, according to Glavin.

The research was funded by the NASA Astrobiology Institute (NAI), which
is administered by NASA's Ames Research Center in Moffett Field, Calif.;
the NASA Cosmochemistry program, the Goddard Center for Astrobiology,
and the NASA Post Doctoral Fellowship program. The team includes Glavin,
Dworkin, Dr. Michael Callahan, and Dr. Jamie Elsila of NASA Goddard.

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Received on Thu 20 Jan 2011 08:48:47 PM PST