It looked like something out of The X-Files, a big hole that had opened up in the clouds over Shepton Mallet, Somerset, on Monday (News, December 2). This unearthly sight was a fallstreak hole, also called a hole-punch cloud.
One case in Russia, in October 2009, caused headlines such as “UFO hovers over Moscow”. But fear not, these holes are simply made by aircraft climbing up or descending through a layer of cloud.
The clouds consist of supercooled water droplets at about minus 15C, but they remain liquid. As an aircraft flies through the cloud, it makes the air expand and cool, and the cloud’s water droplets freeze into tiny ice particles that tumble out of the cloud leaving a large hole behind. This