Ever since the Miller-Urey experiment in 1953, most scientists have held the view that life arose on the
early Earth from simple inorganic molecules. With a suitable energy source (e.g. lightning) and a
hospitable environment (e.g. oceans), complex organic molecules such as sugars and amino acids are
thought to have originated from methane, hydrogen, and ammonia. These organic molecules then
formed the basis of life as we have today.
However, recent astronomical observations have discovered that complex organic molecules exist in
stellar environments. Using the European Space Agency’s Infrared Space Observatory, astronomers
Sun Kwok and Kevin Volk (University of Calgary) and Bruce Hrivnak (Valparaiso University) have found
signatures of organic molecules with aliphatic and aromatic structures in the circumstellar envelopes
of old stars. In a paper that they presented at the American Astronomical Society meeting today in
Atlanta, they showed that chemical synthesis can occur rapidly. Over a period of only several
thousand years, small organic molecules with aliphatic structures are shown to have evolved into
large, complex aromatic molecules. They were able to come to this conclusion by comparing the
infrared spectra of very evolved red giants, proto-planetary nebulae, and planetary nebulae. Since only
a few thousand years in evolutionary time separate these stars, their different infrared spectra give
the most direct evidence of chemical synthesis in stars.
“Although we do not understand how chemical reactions can occur so efficiently in such a low density
environment”, said Dr. Kwok, “there is no doubt that such complex molecules exist, and the stars are
able to make them with no difficulty”. In the last 15 years, Drs. Kwok and Hrivnak have pioneered the
study of proto-planetary nebulae, and these stars have turned out to be rich in complex molecules.
Since these stars are very short lived, the molecules present in their circumstellar envelopes must have
been manufactured recently. The chemical pathway begins with the synthesis of acetylene, which is
detected in the envelopes of red giants. Acetylene then serve as the building blocks for aromatic
molecules such as benzene and more complicated aromatic hydrocarbons.
Since these molecules are eventually ejected into the interstellar medium, it is quite possible that some
of them will end up on planets such as the Earth. If this is the case, life on Earth could have an easier
start than previously believed.
The detection of such complex organic molecules in stellar envelopes also leads to the speculation that
even amino acids could be synthesised, although the detection of such molecules is beyond the
capabilities of the current generation of space telescopes. Should such molecules oneday be found in
the envelopes of old stars, they could provide a pathway such that life could indeed be common in the
universe.
This work was supported by the Natural Sciences and Engineering Research Council of Canada and
NASA.
For more information, please contact Dr. Sun Kwok by telephone at 1-403-220-5414 (office),
1-403-830-8395 (cell), or by email at
kwok@iras.ucalgary.ca.
IMAGE CAPTION: [http://www.iras.ucalgary.ca/~kwok/Image1.jpg]
The Water Lily Nebula in the constellation of Ara is one of the proto-planetary nebulae where complex
organic molecules with aliphatic and aromatic structures are found. This picture was taken with the
Hubble Space Telescope Wide Field Planetary Camera on June 28, 1999. Photo credit: Sun Kwok, Bruce
Hrivnak, and Kate Su.
