The universe might not be infinite, but it continues to expand (at a rate of around 73 kilometers per second per megaparsec) — if that tells you anything. The observable universe is already 93 billion light-years in diameter, and scientists believe there is much more space outside that area. 

Knowing this, it is hard to believe we are alone in the universe, and many scientists think we are not. This doesn't mean they believe in the existence of "little green men," though. Alien life can take many forms. In fact, NASA Chief Scientist Ellen Stofan expects to find evidence of extraterrestrial microbes in about 20-30 years.

In the meantime, people want answers, leading them to find evidence for alien life through scientific, pseudoscientific, or even bizarre means.

Here are some of the most debated and controversial claims of evidence for alien life.

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