According to news reports, an Austrian farmer discovered a mysterious, deep, perfectly round hole that apparently had appeared in his field overnight. And, of course, extraterrestrial activity was assumed.

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Intrigued, Knoglinger used a rope to lower a magnet into the hole, and he concluded that whatever was at the bottom was metallic. This only deepened the puzzle, and soon the mystery drew local, national and, finally, international attention. Curiosity-seekers, geologists and UFO buffs flocked to the farm to see the hole for themselves. A buried UFO became a favorite explanation.

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Part of the answer is that an extraterrestrial craft has become a default explanation in recent years for any large unknown (and presumably round and/or metallic) object. For example, a large round object was recorded on sonar on the ocean floor by a Swedish archaeology team last year. The image has not been confirmed as real (and many experts suspect it's actually a false reading), but by far the most popular explanation is that the round object is a spacecraft. Human imagination almost always creates far more exotic and interesting possibilities than reality can provide, and anything just out of reach, be it deep underwater or underground, can conjure visions of alien spaceships.

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