2000 Annual Science Report
NASA Ames Research Center Reporting | JUL 1999 – JUN 2000
Chemical Building Blocks
We are making significant progress in our studies on the photochemistry of realistic interstellar and cometary ice analogs. Ultraviolet irradiation of these ices at temperatures close to absolute zero, the temperature in deep space, produces a mixture of organic molecules which are far more complex than the simple parent species. We believe this mixture, a refractory organic residue, is similar in nature to the complex organics that potentially rain down on habitable planets in interplanetary dust particles (IDPs), comet dust particles and perhaps even in some meteorites. The key question is, “Could these have played a role in the origin of life?” Until recently this seemed a very long shot. This conclusion is now being reconsidered and our results are an important part of this reconsideration.
Our ice studies proceed along two fronts. Ice studies which contain polycyclic aromatic hydrocarbons (PAHs) and those which do not. PAHs are widespread throughout the interstellar medium and we are the first to study their ice photochemistry under interstellar and early Solar System conditions. In non-PAH containing ices, we find that compounds are produced which self-organize into vesicles (primitive protocells) when the residue is exposed to liquid water, in a fashion similar to that when, say, an IDP falls down into water on a habitable planet. Further, other compounds produced luminesce, they capture ultraviolet light and internally convert that energy into other states. That is, we make compounds that have the ability to harvest energy from the environment. Both vesicle formation and energy harvesting are considered critical in the origin of life, and we have shown that this chemistry takes place under the harshest conditions imaginable in deep space. Thus, the implication is that this level of chemical complexity is widespread throughout the cosmos. We do not yet know the identity of these compounds and have just started this aspect of the investigation, looking specifically for biogenic compounds. In our study of the photochemistry of PAHs in water ice we have shown that biogenic compounds used in living systems today are produced. All of these results have very important implications for the origin of life.
PROJECT MEMBERS:Louis Allamandola
RELATED OBJECTIVES:Objective 1.0
Determine whether the atmosphere of the early Earth, hydrothermal systems or exogenous matter were significant sources of organic matter.
Develop and test plausible pathways by which ancient counterparts of membrane systems, proteins and nucleic acids were synthesized from simpler precursors and assembled into protocells.
Determine (theoretically and empirically) the ultimate outcome of the planet-forming process around other stars, especially the habitable ones.
Define an array of astronomically detectable spectroscopic features that indicate habitable conditions and/or the presence of life on an extrasolar planet.