17 Jan 2000

Sun Kwok and Kevin Wolk, from the University of Calgary (Canada), and Bruce Hrivnak, at Valparaiso University (Indiana, USA), 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.

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 aminoacids 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.

Contacts
Martin Kessler
ISO Project Scientist
mkessleriso.vilspa.esa.es
Tel: +34 91 8131253, +34 91 8131254