A UFO is said to have left this triangular mark after landing in a Norwegian fjord. Cases in which UFOs reportedly interact with the environment in some way are called close encounters of the second kind.

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UFOs have been reported for thousands of years. Of course, this raises the question, "Where's the proof?" The great challenge to those who study UFOs is to sort out the bogus claims from the worthwhile UFO reports. Investigators and ufologists have examined everything from old cave paintings to crash sites to modern-day photographs and video footage. And in light of the many UFO hoaxes that have surfaced over the years, they are right to be wary of outrageous claims.

In the past, the government has taken the search for UFO evidence seriously. After the Roswell crash, government research teams like Project Sign and Project Blue Book were charged with investigating high-profile UFO sightings. This active role in UFO research lasted until the Condon Report, which advised that no further investigation was needed.

But while the government's role may have "officially" ended, who knows what investigations they undertake away from the public eye? Conspiracy theorists might have you believe they've been holding the evidence all the while.­

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