Observations from above the atmosphere are needed for a number of small 

 molecules in both diffuse and dense interstellar clouds. Not only are observa- 

 tions of molecules of direct exobiological interest such as H 2 and 2 needed, 

 but many other molecules whose study is important to obtain an understanding 

 of the chemical and physical conditions in interstellar space are unobservable 

 from the ground. 



The unambiguous observation of increasingly complex molecules in the 

 interstellar medium will not be achieved easily. Difficulties exist in every region 

 of the electromagnetic spectrum considered. In the realm of radio astronomy, 

 the most likely wavelength region appears to be at low frequencies. These fre- 

 quencies do not require telescopes on satellite platforms, but are quite accessible 

 from the Earth. Certainly, as current receiver technology improves, it should be 

 possible to extend the size of the molecules currently detected in the microwave 

 range. In addition, it might be possible to detect functional groups of complex 

 species or even the species themselves via low-resolution infrared spectroscopy, 

 and even visible and ultraviolet studies will be significantly enhanced via space- 

 based observatories such as HST, SI RTF, and LDR. The more complex the 

 organic chemistry detected in interstellar clouds, the more interesting the inter- 

 stellar medium becomes to exobiologists. 



Suggestions for Further Reading 



Irvine, W. M.; Schloerb, F. P.; Hjalmarson, A.; and Herbst, E.: In Protostars 

 and Protoplanets II, D. C. Black and M. S. Matthews, eds., University of Arizona 

 Press, Tucson, 1985. 



Winnewisser, G.; and Herbst, E.: Organic Molecules in Space. Topics in 

 Current Chemistry, vol. 1 39, 1 987, p. 1 1 9. 



Herbst, E.: On the Formation and Observation of Complex Interstellar 

 Molecules. Origins of Life, vol. 16, 1985, p. 3. 



3.10 Interstellar Dust 



Small, solid particles (dust) must have played an important role in determin- 

 ing which biogenic compounds were incorporated into the early solar nebula and 

 at which stage of chemical processing. The exact role dust played cannot be 

 understood until the nature of interstellar and circumstellar dust has been deter- 

 mined. Was dust the bulk source of carbon? Was the dust siliceous but coated 

 with an icy organic mantle? What volatiles were trapped within grains? How big 

 were the grains before and after passage through the accretion shock? Collected 

 specimens of interstellar dust particles and remote observations of many physi- 

 cally different environments may answer these questions. Interstellar dust can 

 be studied through its interaction with electromagnetic radiation by measuring 



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