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"?

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    $\begingroup$ This article has some information on how Mars has a magnetic field. Can't find too much beyond that. $\endgroup$ – Phiteros Jul 24 '18 at 3:49
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    $\begingroup$ Not an answer because I only know one of the three pieces, but - the bow shock in this case is produced by solar winds slamming into the atmosphere. It isn't the same phenomenon for each planet: Earth's is a plasma sheath protecting the gaseous region we'd call the atmosphere, whereas Mars's is more the shape that plasmas create as gas ionizes and is sandblasted away. Both fit the term "bow shock", though, in that the solar wind has a discontinuity before the planet and that region trails out behind it. svs.gsfc.nasa.gov/cgi-bin/details.cgi?aid=4393 $\endgroup$ – Bear Jul 24 '18 at 16:38
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    $\begingroup$ Hydrogen Corona - It's quite outside my knowledge level. But might be a fit for you :). Has a lot to do with something called a "hydrogen line" called the Lyman-alpha $\endgroup$ – Magic Octopus Urn May 13 at 20:42

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