154 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1963 



Hawkins. The results of this study can be correlated with meteorite 

 size and velocity distributions from other investigations. 



MeteoritiG science. — The solar system contains much meteoric 

 matter. The Observatory applies a vast range of teclmiques and 

 instrumentation in its broad meteoritic research progi-am. Investi- 

 gations include the nature of meteoritic matter in the solar system, 

 the theory of meteors in the earth's atmosphere, observation of meteors 

 by optical and radar instruments, mineralogical analyses of meteor- 

 ites, metallurgical analyses of meteorites, and finally observations of 

 artificial bodies simulating meteorites. 



During the past year Dr. Whipple has made new calculations of 

 the frequencies of small bodies near the earth and their penetrating 

 powers on thin surfaces in space. The measurements made in a NASA 

 satellite have confirmed the general order of magnitude of the new 

 calculations, which have reduced the meteoritic hazard by some three 

 orders of magnitude since early calculations. In these and other 

 overall studies of meteoric matter in the solar system. Dr. Wliipple 

 draws on specific results from the diverse meteoritic investigations 

 in which he cooperates as director of the Observatory. 



Dr. Richard B. Southworth has formulated a convenient quantita- 

 tive description for the steady-state space distribution of particles 

 under the Poynting-Robertson effect. Using this description and 

 results from analyses of Comet Arend-Roland, he is studying genera- 

 tion of the zodiacal cloud by cometary dust. 



Robert E. Briggs is now extending previous work on the space 

 distribution of interplanetary particles to include a study of velocity 

 distributions. 



Research into the concentration of micrometeorites in the vicinity 

 of the earth continues. The many-pronged effort of Drs. Colombo 

 and Lautman consists of: (a) Evaluation of the amount of dust 

 placed into orbit aromid the earth as a result of meteors colliding 

 with the m.oon and ejecting material; (b) gravitational focusing of 

 interplanetary particles by the earth, the direct capture of inter- 

 planetary particles moving mider the influence of the gravitational 

 fields of the sun and earth, and the Poynting-Robertson effect; and 

 (c) capture of particles by the combined effects of gravity, atmos- 

 pheric drag, and radiation pressure. 



When particles from space plunge into the earth's atmosphere, 

 they generate a trail of luminosity and ionization. Several scientists 

 of the Observatory continue to work on the physical theory of meteors. 

 Theoretical studies are being made by Drs. Cook, Hawkins, Richard 

 E. McCrosky, and Franco Verniani. Most of these studies are closely 

 linked with analyses of observational data.^' ^' ^ 



I 



See footnotes on p. 164. 



