Static electricity in the atmosphere will not increase during the giant comet's approach, nor afterwards, but during the passage lightning will seem to be almost constant in some places. Humans are familiar with arcing, where two poles or points are electrified, carrying an electric current, and suddenly the air between them is filled with a minor lightning bolt - zap. This is, of course, what causes lightning in the first place, an uneven distribution of electricity between natural conductors, between a buildup in the clouds and the water table below the Earth. What allows lightning to find its path? It is using a little understood path formed by sub-atomic particles, electrical waves of a sort, that have not been measured yet by Earth's human scientists. These emanate from any highly electrified field, and when they touch the arc is now possible.
The path between the Earth and its passing brother, the giant comet known as the 12 Planet, will be so electrified at points, and because the Earth's upper atmosphere will be in motion, bombarded by the comet's tail, static electricity accumulates. This would be devastating to the Earth if the static electricity had accumulated on the passing 12th Planet, a monster compared to the Earth, but the opposite is the case. The static electricity passes from the Earth to her brother, and causes fantastic lightning displays in his upper atmosphere. As this planet is primarily a water planet, this seldom presents a danger to the inhabitants. This period when static electricity can pass is brief, a few hours, and occurs when the Earth's inhabitants are, essentially, fighting for their lives, so they barely take notice. How does a lightning bolt pass some 14 million miles across space? It doesn't, not in that form. In space, not having water vapor and other particles to interact with, there is no spontaneous release of light and heat, no flash and crackle, just the passage of electric particles in all the various sub-atomic components that comprise an electrical current.