Ever since the Miller-Urey experiment in 1953, 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 evolution 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 current generation of space telescopes. Should such molecules be found in the future, life could indeed be common in the universe.
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 is taken with the Hubble Space Telescope Wide Field
Planetary Camera on June 28, 1999.
Photo credit: Sun Kwok, Bruce Hrivnak, and Kate Su.
Other color images can be obtained over the internet via
This work was supported by the Natural Sciences and Engineering Research Council of Canada, the Canadian Space Agency, and NASA.
For more information, please contact:
Dr. Sun Kwok
Dept. of Physics & Astronomy
University of Calgary 2
500 University Drive N.W.
office: (403) 220-5414
cell: (403) 830-8395