Cetacean Probe

The Cetacean Probe was a probe of unknown origin that visited Earth in 2286. It attempted to establish communications with the extinct humpback whales, and when it received no answer, began to vaporize Earth's oceans. Realizing that the only way to stop the probe was to answer it, Admiral James T. Kirk of the HMS Bounty traveled back in time to 1986 and retrieved George and Gracie to respond to the Probe. (TOS movie: Star Trek IV: The Voyage Home)

A year later, the crew of the USS Enterprise-A encountered the Probe again during a joint Federation-Romulan archeological expedition. (TOS novel: Probe)