The basic molecules
of life are scattered through the universe, collecting in faraway
galactic clouds, on passing comets
and asteroids,
and on the planets here in our solar system.
But scientists
still don't know how these molecules came to be, or how they originally came
together to form life. Now, for the first time ever, astronomers have found
some of the basic
compounds necessary to build organic molecules, proteins, and DNA within
the inner regions of a planet-forming disk.
"We see prebiotic organic molecules in comets and the gas giant
planets in our own solar system and wonder, where did these chemicals come
from?" said Marc Kassis, support astronomer at the W.
M. Keck Observatory. "The Spitzer Space Telescope is letting us study these
young stellar objects in new and revealing ways, giving us exciting clues about
where life may form in the universe."
The object--IRS 46--is located in the Milky Way galaxy,
about 375 light years from Earth, in the constellation Ophiuchus.
The researchers
detected two organic compounds--acetylene and hydrogen cyanide--in amounts nearly
10,000 times higher than found in the cold interstellar gas where stars are
born. These compounds are commonly found in the atmospheres
of the giant gas planets in our solar system, the icy surfaces of comets,
and the atmosphere of Saturn's largest moon, Titan. They also detected carbon
dioxide, which is widespread in the atmospheres of Venus, Earth, and Mars.
The presence of
gas-rich disks around young stars is well known, but little is understood about
their chemical structure. The discovery of acetylene and hydrogen cyanide in
one of these disks will help astronomers better understand them and where
future solar systems may someday form and possibly result in life.
"If you add
hydrogen cyanide, acetylene and water together in a test tube, and give them an
appropriate surface on which to be concentrated and react, you'll get a slew of
organic compounds including amino acids and a DNA purine
base called adenine," said co-author Geoffrey Blake of the California
Institute of Technology in Pasadena. "Now, we can detect these same molecules
in the planet zone of a star hundreds of light-years away."
The dust and gas
surrounding a young star blocks visible light, but lets longer wavelengths,
such as infrared light, pass through. Astronomers can find out what this gas
and dust is made of by separating the light into its component wavelengths.
Astronomers have
used this technique since study molecular compounds in protoplanetary
disks of young stellar objects. The Spitzer "c2d legacy program" has looked at
more than 100 sources in five nearby star-forming regions and only IRS 46 showed clear evidence of containing the
organic compounds in the warm regions close to the star where terrestrial planets
are most likely to form.
The results also
indicate the presence of a stellar wind coming from the inner region of the
disk orbiting IRS 46. The wind may eventually blow away the dusty debris in the
disk, perhaps revealing the presence of rocky, Earth-like planets in several
million years.
"This infant
system might look a lot like ours did billions of years ago, before life arose
on Earth," said study leader Fred Lahuis of Leiden Observatory in the Netherlands and the SRON
Netherlands Institute for Space Research.
These findings will
be published in an upcoming issue of the Astrophysical Journal Letters.
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