Dust cloud lightning in extraterrestrial atmospheres

摘要

Lightning is present in all solar system planets which form clouds in their atmospheres. Cloud formation outside our solar system is possible in objects with much higher temperatures than on Earth or on Jupiter: Brown dwarfs and giant extrasolar gas planets form clouds made of mixed materials and a large spectrum of grain sizes. These clouds are globally neutral but we argue that mineral clouds in brown dwarfs and extrasolar planets are susceptible to local discharge events and that the upper cloud layers are most suitable for powerful lightning-like discharges. We discuss various sources of atmospheric ionisation, including thermal ionisation and a first estimate of ionisation by cosmic rays, and argue that we should expect thunderstorms also in the atmospheres of brown dwarfs and giant gas planets which contain mineral clouds.