The Life Cycle of Organic Matter The interstellar medium, with its molecules and dust particles, represents the raw material for forming future generations of stars which may develop planetary systems like our own. The discoveries of protoplanetary disks (see the images) around other stars show that our solar system is no longer the only known example of a planetary system in the Universe. This is supported by the detection so far of about 70 exoplanets circling other stars. Organic matter: from stars to planets, comets and meteorites The life cycle of organic matter (in gaseous form and as solids) is closely connected with the evolution of stars and planets. During star formation, interstellar molecules and dust become the building blocks for protostellar disks, from which planets, comets, asteroids and other macroscopic bodies form. Hyakutake in 1996 and Hale-Bopp in 1997), the chemical composition of comets has been better determined and has been found to be remarkably similar to that found in star-forming clouds. Over a century ago, it was established that some meteorites - other relics from the formation of our solar system - contain carbonaceous material. These carbonaceous chondrites contain a few percent of carbon and some of them exhibit a large variety of organic compounds. Isotopic analysis shows that grains found in primitive meteorites are formed in stellar atmospheres and thus represent samples of ancient stardust. Pristine material in the solar system Small bodies in the solar system, such as comets, asteroids and their fragments (e.g. meteorites, interplanetary dust particles) carry pristine material left over from the solar system formation process, thus sampling the molecular cloud material out of which the sun and planets formed. To search for organic matter in the different space environments therefore allows us to address the basic questions of our existence and to determine the nature of the material which impacted the young planets. External delivery of organic material is now widely accepted as an alternative or additional pathway to the internal production of such material on the early Earth and it may have contributed to the start of life, see the schematic diagram to the right.

Numerous protoplanetary disks have been imaged with the Hubble Space Telescope (HST) indicating that the formation of extrasolar systems similar to our own solar system is a rather common process. The cycle of organic molecules in the universe. Interstellar organics are formed in the interstellar gas, in stellar outflows and on dust grains. This organic material is integrated in the Solar System, is partly chemically processed and/or destroyed. In the final stage of stars, dust and elements are returned to the interstellar medium. Organic molecules formed during this dust cycle may have seeded the young Earth.