http://www.cnn.com/2006/TECH/science/06/02/red.rain/index.html
A bunch of red rain fell over India in 2001, and scientists didn't know why it was red. One scientist looked at it under a microscope, and has asked others, and no one knows what the hell they are. The current theory is that extraterrestrial bacteria fell from a passing comet and mixed in with the clouds and came down as rain. What do you think?