Alien Imagination

Beliefs that some unidentified flying objects are of extraterrestrial origin (extraterrestrial hypothesis), along with claims of alien abduction, are considered spurious by most scientists. Most UFO sightings are explained either as sightings of Earth-based aircraft or known astronomical objects, or as hoaxes. Some sightings have remained unexplained, in some cases having been reported by trained professionals.
Several theories have been proposed about the possible basis of alien life from a biochemical, evolutionary or morphological viewpoint.
Alien life, such as bacteria, has been theorized by scientists such as Carl Sagan to exist in the Solar System and quite possibly throughout the Universe. No samples have been found, although there is some controversy about possible traces of life in Martian material (life on Mars), of which the most famous are on the Allan Hills 84001 meteorite. The term traces its etymological roots to two Latin words: extra ("beyond", or "not of") and‎ terrestrial ("of or belonging to Earth"). Despite the term's popularity, its antonym, extracelestial ("belonging to or from Earth"), is rarely used.