Mysterious Whirlwinds

Have flying saucers landed on Earth? Besides the hundreds of reports of weird lights in the night sky and bizarre flying machines seen by day; people convinced that creatures from outer space are constantly visiting our planet have pointed to one incontrovertibly objective piece of evidence for their claim: the curious round, flattened areas found in fields of crops all over the world.

Discoveries of 'crop circles' have often coincided with reports of unidentified flying objects (UFOs). And the circles usually seem to be made at night. So some believers in UFOs say the circles are the traces of secret landings by alien spacecraft. This is a more plausible explanation than another theory put forward in Britain: that vast herds of hedgehogs had tramped out the circles.

Meteorologists have noted that crop circles bear the classic marks of minor tornadoes: they show clear signs of a circular motion in whatever made them, and a sharp cut-off point between affected and untouched areas. But tornadoes are extremely destructive, and the crops, although flattened, are left undamaged. And tornadoes move along the ground - whatever causes this phenomenon leaves no other trace of its passing.

Nonetheless, scientists from Britain's Tornado and Storm Research Organisation believe that some form of atmospheric vortex or whirlwind, for it seems to consume all its energy as it strikes the ground. They say that it may take decades to work out exactly what makes the circles.