The Seeds of Life - Exogenous Delivery of Organics to Earth
Pascale Ehrenfreund (Space Policy Institute)
The variety of interstellar environments offers many chemical pathways that lead to the formation of carbon compounds. Observations throughout the electromagnetic spectrum show a large variety of organic molecules in interstellar clouds. Simple molecules such as CO, CH, CN, OH, C2, C3 as well as more complex organics including nitriles, aldehydes and alcohols are identified. The most abundant interstellar carbon fraction, macromolecular carbon and polycyclic aromatic hydrocarbons, is produced in interstellar and circumstellar regions. Our solar system was formed about 4.6 Gyr ago through the gravitational collapse of an interstellar cloud. Recent data from the Stardust mission confirmed large-scale mixing in the solar nebula. Thus, the carbonaceous inventory of our solar system represents a mixture of materials including: (i) highly processed material that was exposed to high temperature and radiation (ii) newly formed compounds and (iii) relative pristine material with strong interstellar heritage. Small bodies, such as comets, asteroids and their fragments, meteorites and interplanetary dust particles (IDPs) bear witness of processes occurring at the time of solar system formation. Carbonaceous meteorites exhibit evidence of thermal and aqueous alteration on their parent bodies. Their insoluble carbon fraction is composed of macromolecular aromatic carbon; their soluble carbon fraction contains carboxylic acids, hydrocarbons, and several of the key prebiotic compounds such as amino acids, nucleobases and polyols. Small bodies delivered large quantities of extraterrestrial material to young terrestrial planetary surfaces in the early history of our solar system that may have provided the material necessary for the emergence of life.