Carbon forms in stars and is ejected into the surrounding space at the end of the star's life. The first organic compounds (such as PAHs) form as a by-product of this stellar death. Following ejection, this carbon-containing material disperses into the surrounding diffuse interstellar medium , where it is modified by different physical and chemical processes. Eventually, much of this material becomes concentrated in "dense" molecular clouds environments that are "dense" for space, but still essentially vacuum compared to normal conditions on the Earth. Stars form in these huge "dense" molecular clouds tens of light years across, but are comprised of microscopic grains of ice. Since it is from these clouds that Suns and ultimately planets form, these grains are the true primoridal material, and Infrared spectroscopy has revealed much of their composition. It turns out that these grains contain many interesting organic compounds - compounds composed primarily of carbon, some like those seen in living systems.

How do life-like molecules form in the depths of space at the freezing temperatues of these clouds, just a few degrees above absolute zero? In the Astrochemistry Laboratory we carry out experiments that reproduce space chemistry in the laboratory. These studies have demonstrated that when one reproduces the ionizing radiation that is common in space, this can cause complex chemistry to occur. The UV photolysis (or cosmic ray irradiation) of even very simple ices can make complex mixtures of complex organics, including compounds that may be of great prebiotic interest. For example, compounds that form membranes, amino acids, from which proteins and thus all life is currently composed, and other molecules such as naphthoquinones, that play important roles in biochemistry, and are believed to have been among the first UV shields used by life on Earth.

The production of prebiotic molecules in the interstellar medium is of little consequence to the origin of, and search for, life unless these molecules can be delivered intact to habitable planets. This requires that they survive the transition from the dense cloud to protostellar nebula and subsequent incorporation into planetesimals, followed by delivery to a planetary surface. The presence of deuterium (heavy hydrogen) in certain molecules in meteorites and cometary and asteroidal dust particles demonstrate that some interstellar organic species do, in fact, survive planetary accretion, and are arriving here at Earth where NASA has collected them. In fact. the molecules mentioned above, as well as sugars and nucleic acid bases are known to be present in meteorites and are probably also present in asteroidal and cometary dust as well.

We are tracing our chemical heritage, from the interstellar cloud that made the Solar System to the start of life on Earth. The molecules from which planets and life are composed originate in the interstellar medium. They are modified on incorporation into the solar nebula, and delivered to the surface of planets by meteorites and dust from asteroids and comets. Of course, once at the surface, many terrestrial processes take over. This image was made by Jason Dworkin back when he was still working with us at NASA Ames.

It is believed that the rate at which the Earth swept up such material may have been a million times higher in the distant past, when life was first arising. Thus, most scientists now believe that extraterrestrial organic molecules may have played a role in setting the stage for Life on Earth by adding reduced carbon materials to the Earth's inventory of prebiotic organics. We, and many other scientists, go a step further and propose that Perhaps this matter from space did more than simply deliver carbon as a starting ingredient for the primordial soup. Rather, we think that the specific molecules may matter, having properties that were of relevance to the rise of life on Earth. Please read our other easy-to-read articles on this subject from the July 1999 issue of Scientific American and the on-line web zineStrange Horizons.

The production of these more complex organics from such simple starting materials as ices of H₂O, CH₃OH, and NH₃ is an observation of great importance. Dense molecular clouds are seen to exist throughout our galaxy, and all planetary systems are believed to form from this material. Thus, the processes being studied in our and other laboratories are universal ones, i.e., the universe is in some sense hardwired to produce large quantities of prebiotic organic materials. The result is the virtual assurance that when new planetary systems are formed, prebiotic organics will be present in the starting materials. We are currently making some very interesting progress in this area and we invite you to keep your eye on this page in the future! Check out this recent article about the origin of life at The economist online.

For more detailed information on our laboratory work on the organics produced by the UV photolysis of astrophysical ices, see:

Bernstein, M. P., Dworkin, J. P., Sandford, S. A., Cooper, G. W., & Allamandola, L. J. (2002). Racemic amino acids from the ultraviolet photolysis of interstellar ice analogues. Nature 416, 401-403.

Dworkin J.P., D. W. Deamer, S. A. Sandford, L. J. Allamandola “Self-Assembling Amphiphilic Molecules: Synthesis in Simulated Interstellar/Precometary Ices” Proceedings of the National Academy of Science, USA. 98: 815-819.

Bernstein, M. P., Sandford, S. A., Allamandola, L. J., Gillette, J. S., Clemett, S. J., & Zare, R. N. (1999). UV Irradiation of Polycyclic Aromatic Hydrocarbons in Ices: Production of Alcohols, Quinones, and Ethers. Science 283, 1135-1138.

Salama, F. (1998). The Diffuse Interstellar Bands: A Tracer For Organics in the Diffuse Interstellar Medium? Origins Life Evol. Biosphere 28, 349-364.

Allamandola, L. J., Bernstein, M. P., & Sandford, S. A. (1997). Photochemical evolution of interstellar/precometary organic material. In Astronomical and Biochemical Origins and the Search for Life in the Universe, C.B. Cosmovici, S. Bowyer, & D. Werthimer (eds.), Proc. 5th International Conf. on Bioastronomy, IAU Coll. #161, Capri, 1-5 July 1996, (Editrice Compositori: Bologna), pp. 23-47.

Bernstein, M. P., Sandford, S. A., Allamandola, L. J., Chang, S., & Scharberg, M. A. (1995). Organic Compounds Produced by Photolysis of Realistic Interstellar and Cometary Ice Analogs Containing Methanol. Astrophys. J. 454, 327-344.

Allamandola, L. J., Sandford, S. A., & Valero, G. (1988). Photochemical and thermal evolution of interstellar/pre-cometary ice analogs. Icarus 76, 225-252.