The solar coronal exosphere (fixed at a level where the mean free path is comparable with the scale height) is shown to act like the sheath in a laboratory discharge, that builds up an excess positive charge and electric field. Equality of flux for the charged particles (protons and electrons) at the exosphere is assumed. The value of exospheric electric potential makes the protons virtually weightless. The exospheric sheath potential accelerates the thermal protons to a velocity of 258 km/sec, with which they coast to the earth. The proton density in transit varies approximately as the inverse square law. Higher velocities and densities are obtained for higher coronal temperatures. An estimate of the exospheric transition region is obtained by applying the hydrodynamic theory of ambipolar diffusion in a gravitational field to the observed coronal density distribution. (Author).

This book features several of the significant scientific debates and controversies that helped develop space science in the early space era. The debates led to significant new understandings of the constituents and processes occurring beyond Earth’s atmosphere, and often opened new research directions. Scientific speculations with their resultant debates have played an important role in the development and furthering of research in general. The book thus has broad intellectual importance in illustrating how science advances. The book includes debates in the subject areas of heliophysics (physics in the cosmic region that covers particles and magnetic fields flowing from the Sun), Earth’s moon, solar system asteroids and comets, and the origin of cosmic gamma-ray bursts. A final chapter describes two important and surprising early scientific discoveries that involved no debates. The target audience for this book includes (a) active and retired space scientists, (b) space enthusiasts, and (c) students as supplemental (or even prime) reading in an introductory astronomy and/or space science course. The topics of the debates and controversies, their resolutions, and their pointing to further research and understanding of nature are of both historical and contemporary interest, appeal, and value.