I just saw the NASA video Mars Proton Aurora below and I'm confused, (which by itself is unremarkable).
Without a planetary magnetic field, what force produces a bow shock in the solar wind at Mars, thereby producing a "proton aurora"? Is it just fluid dynamics and proton-proton collisions? Is large (planetary) scale Coulomb repulsion important as well? Does the dynamics also produce a weak secondary magnetic field that participates?
And what (the heck) is a "hydrogen corona"?