Exobiology 



— Space Station Cosmic Dust Collection Facility 



— Space Station Gas Grain Simulation Facility. 



The Life Sciences, Solar System Exploration, and Astrophysics Divisions in 

 OSSA should enhance their support of ground-based interdisciplinary 

 research on the biogenic elements and compounds through ongoing 

 astronomical observations, laboratory and computer simulations of organic 

 cosmochemical processes, and investigations into the origins of biogenic 

 compounds and phases in meteorites and cosmic dust. 



Prebiological Evolution 



This evolutionary epoch spans the time from the formation of Earth to the origin 

 of life. The research goals for this period are twofold: 1) to understand what 

 conditions were like on the early Earth at the time of the origin of life and how 

 these conditions developed as a result of planetary processes operating over time; 

 2) to understand how metabolic and genetic systems originated and were 

 incorporated into primitive cellular life forms under conditions that prevailed on 

 the primitive Earth. Opportunities to seek evidence of chemical evolution or the 

 possible origin of life on other planets will be provided by the Titan/Cassini, Mars 

 Observer, and Mars Rover/Sample Return Missions. Use of the Great Observa- 

 tories and an Astrometric Telescope or a Circumstellar Imaging Telescope will 

 permit the detection of extra-solar planetary systems. Opportunities to learn about 

 conditions on the prebiotic Earth are also likely to be obtained from missions to 

 Mars, the Moon, and other bodies in the solar system. 



A gap in the geological record exists between the formation of Earth 4.5 billion 

 years ago and the oldest rocks, with ages of 3.8 billion years. Fossil evidence from 

 3.5-billion-year-old sediments indicates the existence of diverse marine microbial 

 ecosystems, thus pointing to the origin of life much earlier in the first billion years 

 of Earth history. The lack of a record for this time means that the environmental 

 conditions must be inferred by extrapolation backward in time from the existing 

 record and forward in time from models of planetary formation and early 

 evolution, or through comparative study of extraterrestrial bodies — Mars, Venus, 

 the Moon, the primitive asteroids and comets, and the satellites of the Giant 

 Planets, especially Titan. 



Data obtained from the Viking missions to Mars are widely interpreted to signify 

 the absence of extant life. The recently detected fluvial features and apparently 

 layered sedimentary deposits, however, have been attributed to the action of liquid 

 water in the first billion years of the planet's history. These observations indicate 

 that Mars was more Earth-like early on. And they hold open the exciting 

 possibility that life also arose on Mars during a more clement climatic period, but 

 then became extinct as the climate changed. For this reason, samples returned to 

 Earth from Mars would be of enormous scientific value for the Exobiology 

 Program. Not only would their analysis permit a more thorough determination of 

 the possible origin of life on Mars, but they would also be invaluable in helping 



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