"Meteorite lightning"

"Meteorite lightning" was the headline for the 4 December 2010 issue of "New Scientist" magazine, when it ran an item on the 16 May 2006 green fireball over Queensland, Australia.

"Space debris falling into the atmosphere may cause mysterious ball lightning.

Thousands of people have seen floating orbs of light, sometimes during thunderstorms, but their origin has never been established.

The weather was clear when Don Vernon, a farmer in Queensland, Australia, spotted two green balls descending from the sky on 16 May 2006. Oddly, the second rolled down a hill, bounced and then vanished.

Stephen Hughes, an astrophysicist at the Queensland University of Technology in Brisbane, says the first was probably a bright meteor caused by debris from comet 73P, which came closer to Earth at that time than any other comer in 20 years. The second, he says, was ball lightning triggered by the meteor.

The cometary debris ionised the atmospheric gas as it passed through, boosting the current that normally flows between the ionosphere, an electrically charged region in the upper atmosphere, and the ground. Hughes believes when the "supercharged" conduit hit the soil, it formed a plasma ball, he argues. (Proceedings of the Royal Society A, DOI 10.10.98/rspa.2010.0409.)
Impacting space junk might also produce the effect, he says.