I hope everyone will keep an eye on this question over the coming months, while also watching for well-focused glow discharge on the surface. Perhaps even visible and sustained electrical arcing where image resolution is sufficient.
Sorry, what? Electrical arcing (or "glow discharge") from what to what? Across parts of the comet, or from the comet into space?
If into space: "arcing" from an isolated object (i.e., one not plugged into a power supply) is a capacitor-discharge problem. If you start off with extra charge, a "current" means the charge is going away (that's what the arc is, it's a current, i.e. charge moving towards a lower voltage.) Given this fact (I call it a "fact" because it's familiar in the laboratory, familiar in space, AND strictly obeys the so-far-known laws of E&M):
a) what makes you say "sustained arcing"? "Sustained" for how long? Please show how you predicted "sustained" time, in light of the standard (again, standard means "repeatedly lab- and space-tested") law of charge conservation.
b) Please show your analysis of the electrical power associated with these discharges. How much power is being dissipated by the visible phenomenon you're predicting? (Please express as a product of voltage and current.) What is the original source for this power? Can you walk us through the *coupling* of this source-power and its conversion to discharge-power, attempting to convince us that energy is conserved and all relevant E&M laws are obeyed at each step?
c) If I am in a laboratory vacuum chamber and interested in knowing where there are voltages, currents, and/or charged particle streams, I would not "look for glow discharges". Instead, I would use standard lab current and field-measuring instruments. Rosetta has a large suite of such instruments, as did Giotto. Do you think the comet is in an charged-up state severe enough to produce "discharges", but somehow invisible to all magnetometers and plasma probes? Please describe this state, including the numbers that motivated you to ignore the plasma instruments AND the numbers that motivated you to claim to make this visible-light "discharge" prediction.

