A couple points to ponder. Several state of discharge in plasma: dark mode (no visible light is generated; other wavelengths may be), glow mode (a "step up" from dark mode; more energetic; visible light is emitted) and arc mode (ostensibly the highest "level" of discharge; akin to lightning, electric sparks, etc.).27. Why the poles cannot discharge the “Big Lightning”, like the Aurora does? The aurora discharge the “electricity” that comes from the sun, which is much more intense then any “fly-by planet”. So why the “Big Lightning” go to the Grand Canyon and not to the aurora?
Auroras, sprites, neon and fluorescent lights are example of "glow mode" discharges.
( Sprites, Elves, and Glow Discharge Tubes)
http://scitation.aip.org/journals/doc/P ... 41_1.shtml
They're "excited" enough to fluoresce, but not "so excited" they can't take it and "pop" (transitioning to "arc mode" and discharging lots of electricity at once in a big, axially confined spark). The "magnetic flux ropes" connecting the sun/Earth in an electrical circuit would be in "dark mode." We generally can't see those, because they're not emitting light (though I wouldn't be surprised if they might emit a bit in other parts of the spectrum...).
The auroras get enough electrical input to enter "glow mode," but not to enter "arc mode," so no big lightning at the poles, currently. As to why Earth and Mars might have chosen what is currently the equator of each as discharge points, I don't know. You'd probably have to ask them (geologically and electrically speaking). An interesting point to note is Earth's EEJ [Equatorial Electrojet] and radiation belts centered around the equator. Might it be that these were part of an interacting circuit? Unknown, but interesting to note nonetheless...
Also, proximity may play a factor. If two charged objects are brought into proximity, their behavior may differ based upon relative charges and distance. IE, as you bring objects closer together or increase their charge at the SAME distance, they may be more likely to discharge, one to the other. So, in that case, if a planet were a charged body, and were to pass increasingly close to another charged body, the closer they get, the more likely they may be to engage in a mutual discharge. In other words, changing the length of the "spark gap" may directly influence ability or proclivity to discharge. Same principle as static electricity on your hand versus a door knob. If you're standing 5 feet away from the door knob, your hand and the door knob could hardly care less about each other. As you walk toward the door and stretch out your hand toward the knob, you decrease the relative spark gap. Once your hand passes a critical point, the difference in charges becomes strong enough to initiate a "discharge." IE, you get within a few inches or centimeters of the knob and suddenly you get an unpleasant shock.
If two bodies came into proximity, the discharge may simply go on wherever is more convenient (where the bodies are closest and the electric field / voltage drop is the greatest)...
It's a good question though, and may help to constrain certain theories based on the stuff being discussed on the Mythology forum. IE, does the fact that EDM gouging may have taken place at the equators constrain where the involved bodies were with respect to each other when the discharge(s) took place? IE, which sides were facing at the time, how close / far they were with respect to each other, relative charge, etc?
Hope that helps a little. Again, I've only skimmed the thread and have to get going, but may check back at some point to see if I've managed to clarify anything (hope so) or simply added confusion (hope I've not made things worse?)...
Cheers,
~Michael Gmirkin