Radiation pressure hypothesis

The idea that microbes could migrate across the universe was supported by scientists with a worldwide reputation, such as H. von Helmholtz, W. Thomson (later Lord Kelvin) and Svante Arrhenius. This hypothesis was still accepted by Arrhenius in the year 1927, when he reported in the Zeitschrift fur Physikalische Chemie on his assumption that thermophilic bacteria could be transported within a few days from Venus (with a calculated surface temperature of 320 K) to the Earth by the radiation pressure of the sun (Arrhenius, 1927). The panspermia hypothesis, which seemed to have disappeared in the intervening decades, was reintroduced in the ideas of Francis Crick (Crick and Orgel, 1973). It still exists in a modified form (see Sect. 11.1.2.4). 

We seem, therefore, to have proved conclusively that, at least in this one reaction, radiation cannot alone be responsible for the process of activation. This experiment, together with the recent observations of Hinshelwood and Thompson, Hinshelwood, Ramsperger and Rice and Ramsperger, which show that typical unimolecular reactions do suffer a diminution in specific reaction rate with decreasing pressure and thus render invalid the powerful argument of Perrin, appears to remove all support from the radiation hypothesis. 

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