If you've ever seen a plane flying overhead, you're probably familiar with the cloud-like path they leave in their wake. They're condensation trails (or "contrails" for short) made up mostly of ice crystals -- but to conspiracy theorists, they're something far more sinister. They call them "chemtrails" and they're supposedly filled with harmful chemicals... According to most major conspiracy theory news sources, chemtrails are a real and persistent threat to human existence. However, beyond that overarching theme, the specific allegations of what's in them are diverse, and frankly quite bizarre. The general idea is that these chemtrails are being used by the government to dump harmful biological agents on the unsuspecting population. Why exactly they're doing that depends on which school of "chemtrail thought" you fall under.

There have long been theories of a mystery Planet X in our solar system, but so far, there is no evidence or proof that Nibiru exists.

So if none of their claims can be backed up scientifically, what do these "chem heads" offer as proof of their theories?

Well, photos like the one above, for example. Several pictures like this have been making their way around the Internet for years. However, they're also not proof of chemtrails. These are just ballast barrels placed on a test plane to collect data on proper weight distribution.