The interstellar medium, the space between the stars, is composed primarily of H and He and constitutes a few percent of the galactic mass. Investigating their organic composition often indicates the nature of the parental body ( Hiroi et al. They are fragments of cometary and asteroidal bodies. 2007 Sephton 2002 Septhon and Botta 2005 for reviews). Carbonaceous chondrites (meteorites) and micrometeorites do contain a variety of organics (e.g., see Alexander et al. Many small organic molecules observed in cometary comae probably originate wholly or partially from the decomposition of larger molecules or particles, indicating that large polymers such as polyoxymethylene and HCN-polymers are present in comets ( Ehrenfreund et al.
More than 50 molecules have been identified in cometary comae ( Crovisier et al.
Organic molecules in the solar system are found in planetary atmospheres and on the surface of many outer solar system moons (e.g., Cruikshank et al.
Circumstellar envelopes are regarded as the largest factories of carbon chemistry in space ( Kwok 2004, 2009). In the denser regions of interstellar space, the so-called interstellar clouds, active chemical pathways form simple and complex carbon molecules from carbon atoms ( van Dishoeck and Blake 1998). 2003).Ĭarbon in space was first produced in stellar interiors in fusion reactions and was later ejected into interstellar and intergalactic space during stellar collapse and supernova explosions. Large carbon abundances are already extrapolated from observations of the strong C and CO lines in the hosts of the most distant quasars ( Bertoldi et al. The first chemical enrichment of the universe may likely be connected to the first generation of stars ( Spaans 2004). Astronomical observations in the last decade have shown that carbonaceous compounds (gaseous molecules and solids) are ubiquitous in our own as well as in distant galaxies ( Ehrenfreund et al. How elements are formed, how complex carbonaceous molecules in space are, what their abundance is and on what timescales they form are crucial questions within cosmochemistry.Ĭarbon is found in space in all its allotropic forms: diamond, graphite, and fullerene ( Cataldo et al. The large quantities of extraterrestrial material delivered to young planetary surfaces during the heavy bombardment phase may have played a key role in life's origin ( Chyba and Sagan 1992, Ehrenfreund et al. The remnant planetesimals in the form of comets and asteroids impacted the young planets in the early history of the solar system ( Gomes et al. During the formation of the solar system, this interstellar organic material was chemically processed and later integrated in the presolar nebula from which planets and small solar system bodies formed. Gas and solid-state chemical reactions form a variety of organic molecules in circumstellar and interstellar environments. Figure 1 shows the cycle of organic molecules in the universe. Our understanding of the evolution of organic molecules-including such compounds-and their voyage from molecular clouds to the early solar system and Earth provides important constraints on the emergence of life on Earth and possibly elsewhere ( Ehrenfreund and Charnley 2000). Carbon is a key element in the evolution of prebiotic material ( Henning and Salama 1998), and becomes biologically interesting in compounds with nitrogen, oxygen and hydrogen.
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