Credit: CC0 Public Domain

If intelligent aliens visit the Earth, it would be one of the most profound events in human history.

Surveys show that nearly half of Americans believe that aliens have visited the Earth, either in the ancient past or recently.

But best estimates place the number of space tourists — those who go to space missions or servers space travel — at between 150 and 400.

And while space flights can boost a nation's economy, they often can make us more vulnerable to natural disasters and public health crises on Earth.

Sure, people and governments claim they send covert or covertly funded UFOs to investigate, but can we trust astronomers?

View Images Collectors at The Astronomy Picture of the Day exhibit a 1931 view of Mars. Illustration by M. Scott Jussim, SkySafari; Historic A. Smithson, via The New Jersey Museum of Natural History

What type of proof is there against aliens?

Two years ago, the Hubble Space Telescope became the first spacecraft to image small brown lights—witches' eyes—that scientists suspected were on the surface of Allende, Chile (A.S. Science and Technology Representative Glen Thomson). The machine has since photographed dozens of potential relics of Martian life.

Even at the most recent congressional hearing on the Hubble science, President Obama left the following question unanswered: "Most of the UFOs that have been reported so far are very dim—can an object as luminous as a star really be lurking in the shadows of an infinite void with much greater speed and efficiency than any missile can reach them?"

As to how UFOs might be distributed and targeted, such as in the isolated backwaters of northern Canada, William Burgess, a communications teacher in Borden, Manitoba, decided to bring in the big guns—him and his amateur astronomy club. Read.me, a webpage that aggregates weather reports and weather balloons, has recently featured multi-day weather balloons from Labrador that appear to cross Canadian skies simultaneously for days at a time, and he ascribes some of the sightings to UFOs.

In Alaska, a balloon-borne television crew recently captured TV image of an unidentified object that looked like a spaceship with four triangular wings at seven-pointed-star coordinates and lasted 50 seconds.

And then there are the near-misses. When the Japanese military shot down a tiny drone hovering over Hokkaido, Japan, during World War II, UFO buffs worldwide picked up keywords like UFO violated "aerial exclusion zone," a code two Japanese pilots wanted to send to explain why the U.S. Navy plane was aligning over their airplane, and other prominent underwater murders and assassinations attributed to the Japanese Air Self Defense Force.

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