Lightning: Thunderbolts from space

 作者:贾涠陔     |      日期:2019-03-15 08:09:01
By Anna Gosline IN THE time it takes to blink, there are 10 flashes of fork lightning in the Earth’s atmosphere. Each bolt travels at around a third of the speed of light, reaches temperatures as hot as the sun’s corona, and carries about 10,000 times as much current as a household circuit. No wonder lightning triggers more than a third of North America’s power cuts each year, and kills hundreds of people worldwide. The sheer electrical power of lightning has had researchers baffled. In 1752, Benjamin Franklin flew a kite into a storm cloud and showed that it became electrically charged. But how the comparatively modest build-up of charge in a cloud has the strength to set off such an impressive light show has been something of a mystery. “Nobody understands what’s going on here. You have a lot of people guessing, but we are really clueless. After a couple of hundred years, it’s actually quite embarrassing,” says Joe Dwyer, who studies lightning at the Florida Institute of Technology in Melbourne. Now the mystery is about to be solved. X-ray emissions detected from lightning bolts have provided the first confirmation of a surprising and once controversial theory: that lightning comes from outer space. Lightning is the release of pent-up charge stored in an electric field. In a thundercloud, electric fields are generated by collisions between ice particles (see “Icy origins”). The bulk of the charge is negative,