Terrestrial Accretion from the Solar Wind

Abstract

A SERIES of communications has appeared in Nature under the above title. We would like to discuss in particular those by de Turville^1,2, who has proposed that the oceans have resulted from the accretion of solar protons, and that by Frith², who summarized recent data on stratospheric water-vapour content and showed that this substantiated the hypothesis of de Turville. We will discuss three main points and cite several others, the combination of which seems to indicate that no more than a minor fraction of the water present in the world's oceans has resulted from the accretion of protons from the solar wind. Our main points are these: (1) The solar wind has been measured, and the flux is a factor 10 lower than that used by de Turville in his first communication, and a factor 100 lower than the value used in his second communication. (2) de Turville fails to consider the possibility of escape of hydrogen from the exosphere, which, even if his other assumptions were correct, means that his accretion value is only an upper limit. (3) The observed increase in the water-vapour mixing ratio in the stratosphere cited by Frith does not necessarily mean that the water is of extra-terrestrial origin. There is evidence of large-scale vertical exchange processes in the polar winter stratosphere which can transport the moisture aloft.