The picture shows the Planeterrella experiment, which allows to reproduce plasma configuration in stellar-planet interaction. Several phenomena can be seen on this picture. The violet colors on the big sphere ( the "star" ) are due to N2+, while the redish light on the little one is due to N2. Both colors are seen in actual aurorae on Earth.
The red "bow" in the middle, between the two spheres, is a bow shock similar to the magnetopause between Earth and the Sun (of course not to scale)
Finally, we can see a direct magnetic reconnection between the two spheres at the bottom.
David Bernard (distributed via imaggeo.egu.eu)