Download found: first amino acid on a comet

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FOUND: FIRST
AMINO ACID ON A
COMET
BY MAGGIE MCKEE
An amino acid has been found on a comet for the
first time, a new analysis of samples from NASA’s
Stardust mission reveals. The discovery confirms
that some of the building blocks of life were
delivered to the early Earth from space.
Amino acids are crucial to life because they form the basis of proteins, the molecules
that run cells. The acids form when organic, carbon-containing compounds and water
are zapped with a source of energy, such as photons – a process that can take place
on Earth or in space.
Previously, researchers have found amino acids in space rocks that fell to Earth as
meteorites, and tentative evidence for the compounds has been detected in interstellar
space. Now, an amino acid called glycine has been definitively traced to an icy comet
for the first time.
“It’s not necessarily surprising, but it’s very satisfying to find it there because it hasn’t
been observed before,” says Jamie Elsila of NASA’s Goddard Space Flight Center,
lead author of the new study. “It’s been looked for [on comets] spectroscopically with
telescopes but the content seems so low you can’t see it that way.”
RAW MATERIALS
With only about 100 billionths of a
gram of glycine to study, the researchers were able to measure the
relative abundance of its carbon
isotopes. It contained more carbon-13 than that found in glycine that
forms on Earth, proving that Stardust’s glycine originated in space.
Dust collector with aerogel
CLOSE STUDY
Comets and asteroids are thought to have bombarded the Earth early in its history, and
the new discovery suggests they carried amino acids with them.
“We are interested in understanding what was on the early Earth when life got started,” Elsila told New Scientist. “We don’t know how life got started … but this adds to
our knowledge of the ingredient pool.”
Jonathan Lunine of the University of Arizona agrees. “Life had to get started with raw
materials,” he told New Scientist. “This provides another source [of those materials].”
The amino acid was found in samples returned to Earth by NASA’s Stardust mission,
which flew by Comet Wild 2 in 2004 to capture particles shed by the 5-kilometre object.
TINY SAMPLE SIZE
The samples in Elsila’s study came from four squares of aluminium foil, each about 1
centimetre across, that sat next to a lightweight sponge-like “aerogel” that was designed to capture dust from the comet’s atmosphere, or coma.
The researchers reported finding several amino acids, as well as nitrogen-containing
organic compounds called amines, on the foil in 2008. But it was not clear whether
the discoveries originated in the comet or whether they were simply contamination
from Earth.
The researchers spent two years trying to find out – a painstaking task since there
BIG HISTORY PROJECT
was so little of the comet dust to
study. In fact, there was not enough
material to trace the source of any
compound except for glycine, the
simplest amino acid.
FOUND: FIRST AMINO ACID ON A COMET “It’s a great piece of laboratory
work,” says Lunine. “It’s probably
something that couldn’t have been
done remotely with a robotic instrument – it points to the value of returning samples.”
Elsila says she would like to see
samples returned not just from a
comet’s coma but from its main
body, or nucleus. “There might be
more complex mixtures [of amino
acids] and higher levels of them in a
comet nucleus,” she told New Scientist.
Europe’s Rosetta spacecraft should
help shed light on the issue. The
first mission designed to orbit and
land on a comet’s nucleus, it will
reach the Comet 67P/ChuryumovGerasimenko in 2014 after a 10-year
journey from Earth.
Comet particle tracks in aerogel.
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Reference
Source
Cover image: A spacecraft is depicted
following a comet from within its tail.
Credit: NASA/JPL-Caltech. Public domain. http://stardust.jpl.nasa.gov/photo/
artist.html#row11
New Scientist, Found: first amino acid
on a comet https://www.newscientist.
com/article/dn17628-found-first-aminoacid-on-a-comet/
Dust collector with aerogel. Credit:
NASA/JPL-Caltech. Public domain.
http://stardust.jpl.nasa.gov/photo/spacecraft.html#aerogel1
Meteoritics & Planetary Science http://
meteoriticalsociety.org/?page_id=34
Comet particle tracks in aerogel. Credit:
NASA/JPL-Caltech. Public domain.
http://stardust.jpl.nasa.gov/news/status/060512.html
BIG HISTORY PROJECT
FOUND: FIRST AMINO ACID ON A COMET 3