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Ancient astronaut theories center around the proposal that the Earth has at some point in the distant past been visited by intelligent extraterrestrial beings, and that furthermore such contact is linked to either the origins of, or their developmental influence on, human cultures, technologies, and religion. Indeed, part of the theory suggests that gods from most, if not all religions, are actually extraterrestrial beings and technologies mistaken for divine entities by primitive man. While no peer-reviewed scientific journals validate any such claims, these theories have been popularized (particularly in the latter half of the 20th century) by authors such as Erich von Däniken and Zecharia Sitchin, among others. Typically proponents of these theories put forward as evidence their interpretations of various archaeological artifacts which they deem to have been anachronistic or 'beyond the (presumed) technical capabilities' attributed to the historical cultures they are associated with (see "OOPArt"). Another common theme relies upon the interpretation of depictions in certain ancient artworks as being representations of actual extraterrestrial visitors as realised by the contacted cultures.

Gaps in the historical and archaeological records and the corresponding absence of definitive explanations in certain contexts from the archaeological sciences are sometimes seized upon by these theorists, as being suggestive that these alternative ideas have a valid basis. Critics of these theories maintain however that such gaps in contemporary knowledge of the past are in no way any kind of demonstration that such alternative accounts are a necessary, or even plausible, conclusion to draw from the (lack of) available data. A number of ancient astronaut claims are made in direct opposition to the consensus scientific interpretation of evidence in situations where there are alternatives supported by more widely accepted theories.
The Dogū (土偶) is speculated to be an Ancient Astronaut that visit earth during the Jomon period, it shows features resembling a space suit, goggles and a space helmet.
The Dogū (土偶) is speculated to be an Ancient Astronaut that visit earth during the Jomon period, it shows features resembling a space suit, goggles and a space helmet.

Ancient astronaut theories may be considered a subset of paleocontact theory, a hypothesis that intelligent extraterrestrials have visited Earth. Carl Sagan, I.S. Shklovskii, and Hermann Oberth are three notable scientists who have seriously considered this possibility.

The scientific community remains generally skeptical and the dominant view is that the evidence for "ancient astronaut" and paleocontact theories is undemonstrated, and that the promotion of these ideas amounts to little more than an exercise in pseudoscientific speculation.[1]