From 1896 to 1917 the Norwegian physicist Kristian Birkeland designed an experiment called the Terrella, which helped him to understand a great deal of the formation mechanism of the polar lights. It consisted in shooting électrons from a duct to a magnetized sphere in a vacuum. In his mind, the electron gun was representing the sun, and the magnetized sphere was naturally representing the Earth. The configuration of his experience allowed him to see also, without identifying the ring current latter on discovered by James Van Allen (which won the Crawford prize from this discovery). We now know that the Solar – terrestrial system is more complex than Birkeland imagined. However, this experiment remains fascinating.

A century later, this experience has been totally redefined by Jean Lilensten, Resarch Director (CNRS) at the Laboratory of Planetology of Grenoble, and his friends, collaborators and PhD students (M. Barthélémy, C. Simon Wedlund, G. Gronoff and P. Jeanjacquot). It has diffused toward other cities thanks to other colleagues. The new design is inspired by Birkeland’s Terrella and remains a demonstrator of the polar lights (aurora). But its great flexibility allows simulating a large amount of the different interactions between the stars and the planets : Uranus and Neptune with their inclined axes, the interaction between Ganymede and Jupiter, jets and stellar rings and even the interaction between a magnetized exoplanet and a nearby star. Therefore, this experience is now the Planeterrella.

The experiment is gorgeous. Circles or auroras fome above the magnetic poles of the sphères. Redish iridescence allow to litterally see the magnetic configurations. It is possible to visualize a ring of particles around the spheres through the production of light, a configuration which had been interpreted by Birkeland as the rings of Saturn.

To dream in front of astrophysical phenomena, to visualize cosmic phenomena ... en route to the Planeterrella !