Recent observations by the Infrared Space Observatory (ISO) have found
evidence of rapid synthesis of complex organic molecules in the late
stages of stellar evolution. The chemical synthesis begins with the
formation of acetylene, the first building block of benzene, in carbon
stars. In a following proto-planetary nebulae stage, emission features
corresponding to stretching and bending modes of aliphatic compounds
are detected. When these objects evolve to become planetary nebulae,
aromatic C-H and C-C stretching and bending modes become strong. These
results show that complex carbonaceous compounds can be produced in a
circumstellar environment over a period of only a few thousand years.
Isotopic analysis of meteorites and interplanetary dust collected in the upper atmospheres have revealed the presence of pre-solar grains similar to those formed in evolved stars. This provides a direct link between star dust and the solar system and raises the possibility that the early solar system was chemically enriched by stellar ejecta.