Exobiology 



How does water interact with organic and inorganic matter in the interstellar 

 medium? What gas and dust species survive transit from their circumstellar site of 

 origin to the ISM? Progress in obtaining answers to these and other questions will 

 require astronomical observations with airborne and spaceborne telescopes, as well 

 as theoretical studies aimed at elucidating the relationship between physical 

 conditions in these environments and the nature and abundance of observed 

 species. 



Astronomical observations and theories of solar system origin indicate that 

 formation of stars and, presumably, associated planetary systems occurs in dense 

 regions of the ISM typically where organic matter and water are seen as 

 molecules in the gas phase and as components of dust grains. The theories 

 suggest, moreover, that physical conditions during evolution of the solar nebula 

 would allow material from the parent interstellar cloud to survive in the outer 

 nebular regions and become incorporated in primitive bodies, such as comets and 

 asteroids. 



Studies of Comet Halley have revealed a variety of simple organic compounds and 

 a fascinating, but poorly characterized, complex mixture of higher molecular 

 weight particles, composed only of various combinations of the elements C, H, O, 

 and N. The simple compounds, including hydrogen cyanide and formaldehyde, 

 are among the most abundant in the interstellar clouds, thus underscoring the 

 probability that comets contain components of interstellar origin. Establishing such 

 origin will require automated spacecraft investigations of comets, as planned for 

 the Comet Rendezvous Asteroid Flyby (CRAF) Mission, and detailed analysis in 

 terrestrial laboratories (see below) of samples returned from the nucleus of a 

 comet, as envisioned for the Rosetta Mission. 



Recent analyses of carbonaceous meteorites and cosmic dust revealed that some of 

 the organic matter in them, including amino and carboxylic acids in one meteorite, 

 contains anomalously high ratios of deuterium to hydrogen approaching those 

 seen only in molecules observed in the ISM. Additional research on samples of 

 meteorites and dust needs to be conducted to determine how widespread such 

 deuterium anomalies are among the classes of organic compounds and among 

 types of samples. These studies should also be expanded to seek anomalies in 

 other biogenic elements. Whether the organic matter containing these isotopic 

 anomalies originated in the ISM or was formed as secondary products in the solar 

 nebula or in the asteroidal parent bodies of the meteorites from interstellar 

 chemical precursors is a central issue that remains to be elucidated. To help 

 resolve this question, more laboratory and computer experiments should be 

 undertaken to simulate the chemistry of these environments. These investigations 

 should yield isotopic and molecular structural criteria suitable for use in 

 distinguishing between various mechanisms and environments of formation when 

 applied to data obtained by astronomical observations and sample analyses. 

 Opportunities to carry out some of these experiments under the microgravity 

 conditions of the Space Station should be exploited (2,4). 



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