Unidentified flying object

An Unidentified Flying Object was a term in use on Earth during the 20th and 21st centuries to explain the presence of an object in Earth's atmosphere or in orbit that could not be explained by the technology in use at the time. Many incidents of UFO sightings were later revealed to be vessels from the 23rd or 24th centuries that had traveled back in time.

In 1947, a vessel owned by Quark crashed in the New Mexico desert near the city of Roswell after being sent back in time from 2372. Considered a UFO by the United States Army, the vessel was impounded by the American forces, and the crew - consisting of Quark, Rom, and Nog - were held by the Americans at Roswell Army Air Field. Odo had also accompanied the Ferengi, but as he was disguised was able to evade capture. With the assistance of Faith Garland and Jeffrey Carlson the visitors from the 24th century were able to escape. The United States later covered up the entire incident by claiming a weather balloon had crashed. (DS9 episode Little Green Men).

The USS Enterprise (NCC-1701) had traveled back in time to the mid 1960s after escaping the gravity of a black star. They had finally regained control of the vessel while in Earth's atmosphere. Meanwhile, United States Air Force officials on the ground were tracking the Enterprise, and sent Captain John Christopher up to investigate this large UFO in Earth's upper atmosphere. (TOS episode Tomorrow is Yesterday).

In 1986, a Klingon Bird of Prey under command of the late USS Enterprise (NCC-1701) decloaked in the Bering Sea. This ship, named the HMS Bounty, was able to prevent the humpback whales George and Gracie from being killed by a whaler operating in the area. A tracking station in Nome, Alaska tracked the Bounty as it left Earth's atmosphere. (Novelization of Star Trek IV: The Voyage Home).