Extraterrestrial lightning phenomena
Lightning, when you get right down to it, is essentially nothing but static electricity on a grand scale. Rising water vapor condenses into droplets or tiny ice crystals, which acquire a static electric charge as they pass through the air. This mechanism is responsible for all the forms of lightning found in thunderstorms–cloud to cloud lightning, cloud to ground lightning, and in-cloud lightning that you'll see during a storm.
The same mechanisms work anywhere water vapor exists in cloud formations. Lightning flashes have been observed in the upper atmospheres of both Jupiter and Saturn, albeit on a far grander scale than the lightning flashes on earth. These gas giants have water vapor in their atmospheres, along with methane, ammonia, and elemental hydrogen and helium. The clouds found on gas giants tend to form in layers, with each layer composed predominantly of different chemical compounds; the outer layer of Jupiter's clouds, for example, is predominantly ammonia, with a second cloud layer beneath it made up mostly of ammonium hydrosulfide (NH4SH), and below that, a layer of water clouds. Jupiter's atmosphere is extraordinarily turbulent, creating plenty of friction for massive lightning discharges in the water cloud layer.
This is interesting stuff, but not all that surprising. The mechanisms for lightning on Jupiter and lightning on earth are very similar, despite the radical differnces in the composition and size of the planets. Water vapor forms clouds, motion of water droplets in the clouds creates static electricity, you get lightning. Neat, but not earth-shaking.
Very recently, however, the European Space Agency's Venus Express probe has confirmed a suspicion many astronomers have had for a long time: You don't need water vapor for lightning. Clouds of sulphuric acid will do just as well.
The ESA's probe has discovered evidence of lightning on Venus, our (relatively) nearby neighboring planet. Venus is an inhospitable place, with high surface temperatures, a crushing atmosphere, and clouds of acid streaming by overhead in ceaseless windstorms stronger than the strongest terrestrial hurricane. And, apparently, lightning.
This artist's conception of cloud to ground lightning on Venus shows a lightning bolt descending from the haze of acidic clouds overhead. The probe only recorded direct evidence of cloud to cloud lightning, high in the sky at an altitude of 55 kilometers, but if the processes underlying lightning on earth are similar, cloud to ground lightning is possible as well.
These findings are significant for two reasons. First, lightning played a strong role in shaping the chemistry of our atmosphere early in our planet's history, and lightning almost certainly has changed the atmospheric composition of Venus as well; understanding Venus' atmosphere requires understanding the lightning that occurs there.
Second, we now know that the process by which water clouds form static electrical potentials is not unique to water. The method by which electrical charges become segregated in thunderheads is not entirely understood, but knowing that the same kind of charge segregation can happen in clouds of sulphuric acid helps give us insight into the process here at home.
Besides, lightning on Venus is just plain cool.