Chemical synthesis of complex organic molecules, the most basic ‘building blocks’ for life, can occur rapidly in
stellar environments, according to results obtained with the European Space Agency’s infrared space
observatory, ISO, and presented last Saturday at the American
Astronomical Society meeting in Atlanta by a team of Canadian-Mexican astronomers.

Sun Kwok and Kevin Wolk, from the University of Calgary, and Bruce Hrivnak, at Valparaiso University,
studied the chemical composition of the circumstellar envelopes of old stars. They chose three types of old
stars which are actually representatives of three different stages of evolution, separated by just a few
thousand years:

* very evolved red giants — the first evolutionary step;

* protoplanetary nebula — the second stage;

* finally, planetary nebula.

By comparing their infrared spectra, in which the signature of molecules can be identified, the researchers
could trace the processes of chemical synthesis leading to different compounds in each stage of the stellar

They found that several thousand years are enough for small organic molecules to evolve into large, complex
organic molecules. For instance acetylene, which is detected in the envelope of red giants, serves as a
building block for molecules such as benzene and more complicated aromatic hydrocarbons present in the
planetary nebula.

“Although we do not understand how chemical reactions can occur so efficiently in such a low density
environment, there is no doubt that complex molecules exist, and the stars are able to make them with no
difficulty”, says Kwok.

According to this researcher, the finding of complex organic molecules in stellar envelopes might provide an
easier explanation for the beginning of life on Earth, since it is quite possible that some of these molecules will
end up on planets. Kwok also suggests that even amino acids could be synthesised in the stellar
environments, although to look for them astronomers will have to wait for future infrared space telescopes
such as ESA’s Far Infrared and Submillimetre Telescope (FIRST), to be launched in 2007.

Footnote about ISO

The European Space Agency’s infrared space observatory, ISO, operated from November 1995 to May
1998, almost a year longer than expected. An unprecedented observatory for infrared astronomy, able to
examine cool and hidden places in the Universe, ISO made nearly 30,000 scientific observations.


Martin Kessler

ISO Project Scientist

Tel: +34 91 8131253, +34 91 8131254


* AAS press release

* ISO science homepage

* More about FIRST



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.