1. Wow! Signal

SETI recently announced that they’re going offline due to lack of funding. Our systematic search for intelligent life elsewhere in the universe is about to end. The Wow! Signal is the one instance where SETI found something, which unfortunately was never repeated or seen again. These six letters, circled and annotated “Wow!” have been the cause of rampant speculation and excitement, but remain elusive as to their meaning and origin. It was a narrowband radio signal, sent for 72 seconds, bearing all the hallmarks of extrasolar and extraterrestrial broadcast. It was never repeated. Nothing like it was ever spotted again. That may (or may not) have been the only contact with extraterrestrial intelligent life that we’ll ever see.