Answer: Martians

During his early radio experiments Nikola Tesla encountered unusual patterns that didn’t match any of the previous signals he had encountered when observing electrical storms and other natural phenomenon. The patterns registered on his radio as a series of clicks that he interpreted as a numerical sequence.

Tesla’s take on these new and unidentified patterns was that they were evidence of his theories that radio waves could be used for interplanetary communication and were potentially Martian in origin. While it’s quite possible Tesla was observing an unidentified natural phenomenon, it’s equally possible that he was picking up radio signals from the only other person on Earth simultaneously experimenting with radio: Guglielmo Marconi.

Although Tesla was criticized in scientific circles of the day for suggesting the phenomenon he observed was a Martian broadcast, history has–in a roundabout way–redeemed him. Nearly a century later, the United States put scientific equipment on Mars that did in fact broadcast back to Earth using the very radio signals Tesla had proposed were suitable for interplanetary communication.