http://www.nasa.gov/mission_pages/stardust/news/stardust_amino_acid.html
NASA
August 17, 2009
NASA scientists have discovered glycine, a fundamental building block of
life, in samples of comet Wild 2 returned by NASA's Stardust spacecraft.
"Glycine is an amino acid used by living organisms to make proteins, and
this is the first time an amino acid has been found in a comet," said
Dr. Jamie Elsila of NASA's Goddard Space Flight Center in Greenbelt, Md.
"Our discovery supports the theory that some of life's ingredients
formed in space and were delivered to Earth long ago by meteorite and
comet impacts."
Elsila is the lead author of a paper on this research accepted for
publication in the journal Meteoritics and Planetary Science. The
research will be presented during the meeting of the American Chemical
Society at the Marriott Metro Center in Washington, DC, August 16.
"The discovery of glycine in a comet supports the idea that the
fundamental building blocks of life are prevalent in space, and
strengthens the argument that life in the universe may be common rather
than rare," said Dr. Carl Pilcher, Director of the NASA Astrobiology
Institute which co-funded the research.
Proteins are the workhorse molecules of life, used in everything from
structures like hair to enzymes, the catalysts that speed up or regulate
chemical reactions. Just as the 26 letters of the alphabet are arranged
in limitless combinations to make words, life uses 20 different amino
acids in a huge variety of arrangements to build millions of different
proteins.
Stardust passed through dense gas and dust surrounding the icy nucleus
of Wild 2 (pronounced "Vilt-2") on January 2, 2004. As the spacecraft
flew through this material, a special collection grid filled with
aerogel – a novel sponge-like material that's more than 99 percent empty
space – gently captured samples of the comet's gas and dust. The grid
was stowed in a capsule which detached from the spacecraft and
parachuted to Earth on January 15, 2006. Since then, scientists around
the world have been busy analyzing the samples to learn the secrets of
comet formation and our solar system's history.
"We actually analyzed aluminum foil from the sides of tiny chambers that
hold the aerogel in the collection grid," said Elsila. "As gas molecules
passed through the aerogel, some stuck to the foil. We spent two years
testing and developing our equipment to make it accurate and sensitive
enough to analyze such incredibly tiny samples."
Earlier, preliminary analysis in the Goddard labs detected glycine in
both the foil and a sample of the aerogel. However, since glycine is
used by terrestrial life, at first the team was unable to rule out
contamination from sources on Earth. "It was possible that the glycine
we found originated from handling or manufacture of the Stardust
spacecraft itself," said Elsila. The new research used isotopic analysis
of the foil to rule out that possibility.
Isotopes are versions of an element with different weights or masses;
for example, the most common carbon atom, Carbon 12, has six protons and
six neutrons in its center (nucleus). However, the Carbon 13 isotope is
heavier because it has an extra neutron in its nucleus. A glycine
molecule from space will tend to have more of the heavier Carbon 13
atoms in it than glycine that's from Earth. That is what the team found.
"We discovered that the Stardust-returned glycine has an
extraterrestrial carbon isotope signature, indicating that it originated
on the comet," said Elsila.
The team includes Dr. Daniel Glavin and Dr. Jason Dworkin of NASA
Goddard. "Based on the foil and aerogel results it is highly probable
that the entire comet-exposed side of the Stardust sample collection
grid is coated with glycine that formed in space," adds Glavin.
"The discovery of amino acids in the returned comet sample is very
exciting and profound," said Stardust Principal Investigator Professor
Donald E. Brownlee of the University of Washington, Seattle, Wash. "It
is also a remarkable triumph that highlights the advancing capabilities
of laboratory studies of primitive extraterrestrial materials."
The research was funded by the NASA Stardust Sample Analysis program and
the NASA Astrobiology Institute. NASA's Jet Propulsion Laboratory,
Pasadena, Calif., manages the Stardust mission for NASA's Science
Mission Directorate, Washington. Lockheed Martin Space Systems, Denver,
developed and operated the spacecraft.
To learn more about the mission, visit http://stardustnext.jpl.nasa.gov/
For more about the NASA Goddard astrobiology team, visit
http://astrobiology.gsfc.nasa.gov/analytical
