The Whale Probe, also known as "The Traveler," was an enormous cylindrical probe sent to Earth to make contact with humpback whales. Who sent it and why was a mystery. Without contact with the great sea mammals, it experienced great pain and sorrow. It emitted high-pitched transmissions of whale songs in its attempt to contact the cetaceans and in the process could disrupt and shut down any starship or space station.
Because humpback whales had been hunted to extinction, the Traveler was unable to contact any on Earth. The Traveler had maintained contact with the whales over vast distances of space, and came to Earth because, during their extinction, it heard their songs of suffering. Misunderstanding the lack of response, and not realizing its transmissions were harmful to humans, it boosted the power of the songs to the point where it began destroying Earth's ionic atmosphere and vaporizing the oceans.
Admiral Kirk and his crew stopped the Traveler by traveling back in time and finding two humpback whales, George and Gracie, and bringing them back to the future. George and Gracie, released into the sea, answered the Traveler's calls. After a lengthy "conversation" wherein the two whales and the Traveler exchanged songs, the probe departed, and menaced the Earth no further.
- The probe's alternate nomenclature of "The Traveler" comes from Vonda N. McIntyre's novelization of Stark Trek IV: The Voyage Home, as does the fact it experiences sadness and pain without contact with whales.