Comets are electrical discharges in the thin plasma that permeates the solar system. Because they spend most of their time far from the Sun, their rocky nuclei are in equilibrium with the voltage at that distance. But as they accelerate in toward the Sun, their voltage is increasingly out of equilibrium with the voltage and increasing density of the solar plasma. A plasma sheath forms around them—the coma and tail. And filamentary currents—jets—between the sheath and the nucleus erode, particle by powdery particle, the circular depressions with terraced walls that are typical of electrical discharge machining. As the discharge channels move across the surface of the comet, they burn it black.

Originally posted by MrPenny
reply to post by internos

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In the full-res image from jpl, that sure does, kinda' sorta', almost, look like the same type of reflection created by the bright objects in the top of the image. Could its apparent movement be created by the motion? With the reflection being cast across the lense?

I wish we had some sober idea what the object in question actually is. I'm leaning toward an optical reflection of the object in the top of the image.