PANSPERMIA 59 



the surfaces of other heavenly bodies. If a planet is inhabited 

 by living organisms, particularly micro-organisms, then their 

 spores would be able to travel through interstellar space in 

 the same way. Arrhenius calculated that bacterial spores 

 having a diameter of 00002-0000 15 mm could travel through 

 space at a very great speed under the influence of the pressure 

 of sunlight. Fourteen months after having left the Earth 

 such a spore would pass out of our planetary system, but it 

 would be 9,000 years before it reached the nearest star, 

 a Centauri. The migration of spores can, however, take place 

 towards the Sun as well as away from it. While wandering 

 in interstellar space the germ may meet comparatively large 

 particles of cosmic dust. If the spore becomes attached to a 

 particle having a diameter of 0-0015 mm it will begin to 

 move towards the Sun, as the pressure of the light will not 

 be able to overcome the weight of the particle which will 

 be approaching the Sun under the influence of gravity. 

 Arrhenius thought that the Earth might have been colonised 

 in this way by spores of micro-organisms coming into our 

 solar system from other parts of the universe. 



According to the calculations of Arrhenius the particles 

 of cosmic dust falling on the Earth in this way would not 

 necessarily get hot and burn in the atmosphere of the Earth 

 as do meteorites. If the particles were of the size mentioned, 

 the pressure of light would check their motion and the speed 

 at which they fell would be slow enough for them only to 

 be heated through some tens of degrees, which would not 

 prevent the spores from retaining their viability. 



Arrhenius' theory received wide attention in the scientific 

 world and found many supporters both among physicists 

 and among biologists. In the U.S.S.R. in particular it was 

 supported by S. Kostychev, P. Lazarev, A. Nemilov'^" and 

 others. In fact, Arrhenius made careful enough calculations 

 and a good analysis of the mechanical aspect of the passage 

 of particles of matter from one heavenly body to another. 

 There remained, however, the unsolved problem of whether 

 the germs of bacteria could accomplish such an interstellar 

 journey and remain alive. To this aspect of the matter 

 Arrhenius and the other supporters of his theory quite 

 naturally paid special attention. 



