The scientific legacy of Hannes Alfvén

Abstract

This year marks 70 years since the publication of a paper with far‐reaching consequences for space and plasma physics: the 1942 letter to Nature by Hannes Alfvén, “Existence of electromagnetic‐hydrodynamic waves.” The letter, which was only half a page long, described a new type of low‐frequency oscillation of a magnetized plasma. The paper was long disregarded or openly rejected, as the new waves that it described could not be demonstrated experimentally at that time. But as experimental techniques improved in the laboratory and experiments in space became possible, it became evident that what are now called Alfvén waves are of fundamental importance in plasma physics in general and space plasma physics in particular. In fact, they constitute a cornerstone of a new field of physics: magneto‐hydrodynamics. Alfvén waves are found in just about every space plasma, such as the Sun, the solar corona, and the solar wind, as well as in magnetospheres of the Earth and other magnetized planets.