It is likely that Carl Sagan was one of the pioneers to adopt the ancient astronaut theory. NASA funded him to conduct research and write an academic paper exploring the possibility of extraterrestrial visits to Earth in the past, in addition to discussing intergalactic travel and other related topics. Written in 1962, the paper is archived at the Library of Congress, although information suggests that NASA and the Pentagon may have influenced efforts to restrict its release.
Professor Avi Loeb is famous not only for his bold conjectures regarding extraterrestrial hypotheses but also for his courage in addressing topics typically avoided by other scientists. He has remained firm in his controversial statements despite criticism from the scientific community. The mystery of our potential solitude in the universe and the possibility of extraterrestrial intelligences have inspired Loeb to explore unconventional ideas.
Previously, astrophysicist Carl Sagan had meticulously discussed and studied this very issue. A renowned name in the scientific community, Sagan was known for his skepticism toward UFOs and extraterrestrial beings. However, his early work suggests that he seriously considered the existence of advanced alien civilizations, their ability to engage in interstellar travel, and even the viability of ancient astronaut visits from other worlds that influenced human history and progress.
His study titled “Establishing Direct Galactic Connections via Relativistic Interstellar Space Travel” addressed topics such as alien life, interstellar travel, and extraterrestrial contact in remote eras—an unconventional subject for the time.
“We assume that there exists in the Galaxy a loosely coherent community of various civilizations collaborating in the exploration and investigation of astronomical objects and their inhabitants. If each advanced civilization sent an interstellar ship annually, the average time between visits to a typical star would be 10^5 years, while for a planetary system with intelligent life it would be 10^4 years, and for another advanced civilization it would be 10^3 years.
Thus, there is a statistical probability that Earth has been visited by an advanced extraterrestrial civilization at least once during its history. Proving this contact through historical records and ancient iconography faces significant challenges. However, legends that could be explored with purpose in this context do exist. Moreover, the possibility of bases or artifacts from interstellar spacefaring civilizations in other parts of the solar system cannot be ruled out. The conclusions of this paper should be considered provisional.”
Although it may seem trivial to some, this is the suggestion made by the renowned astrophysicist in one of his papers. In his analysis, Sagan explained that humanity needs to find a way to thrive in the future, employing advanced technology and avoiding nuclear conflicts. According to the paper, Sagan estimates that there are currently about one million advanced civilizations in the Milky Way.

In the 18-page paper, Sagan provides mathematical equations to support his speculation about intergalactic travel, along with historical references and sources that corroborate the “Ancient Astronauts” theory. This theory posits that advanced extraterrestrial civilizations visited humanity over thousands of years.
The Ancient Aliens theory originated in the 1950s, long before Erich von Däniken wrote his book Chariots of the Gods?. Sagan disagreed with that book, but he did not dismiss the possibility of extraterrestrial civilizations visiting Earth. As a scientist, he proposed that the idea of extraterrestrial encounters discussed in the book was not based on solid theory. The Drake and Fermi equations were an initial step in this theory. If alien life exists and intergalactic travel is feasible, then it is logical that, at some point in the past, we might have been visited by beings from other planets. Investigating historical records of possible encounters becomes relevant.
The paper written by Sagan mentions several specifics present in Sumerian traditions, which could be interpreted through the lens of his theory. These ideas earned Sagan mockery from colleagues and friends. He faced obstacles at Harvard and other institutions, which is surprising given his intellectual level. There were indications that NASA, influenced by the Pentagon, attempted to control Sagan.
Donald L. Zygutis, a scholar with 40 years of experience analyzing Carl Sagan’s work, wrote the book The Sagan Conspiracy, in which he presents a convincing argument pointing to a possible suppression by the Pentagon and NASA, who might have concealed Sagan’s work shortly after it was written.
But why would NASA and the Pentagon care? The academic community holds a fundamental rule: intergalactic travel is impossible. Anyone who challenges the establishment’s norms is often rejected. John E. Mack, a psychiatrist and Nobel Peace Prize laureate, wrote the book Abductions: Human Encounters with Aliens. The opposition to him exceeded what would be proportionate for a respected academic.
Surprisingly, in 2014, NASA itself published a book titled Archaeology, Anthropology, and Intergalactic, which explores extraterrestrial interference in human history. The book suggests the possibility that certain representations of rock art on Earth may have extraterrestrial origins. The work was edited by Douglas Vakoch, director of the Search for Extraterrestrial Intelligence (SETI).

Douglas Vakoch, in his work, raises concerns about the complexities that might arise with the potential first contact with an alien civilization.
“If, in a modern SETI experiment, we capture a radio signal, we might confirm the existence of another intelligence, but the content of the message will remain uncertain. Rapid fluctuations and information-laden encoding in radio signals could be attenuated when capturing weak signals over long periods, increasing the probability of detection but sacrificing the content these signals carry.
Even if we managed to identify a civilization orbiting a nearby star, their signals would have traveled billions of kilometers, reaching Earth after years of travel.”
“To go beyond merely detecting such intelligence and actually have a chance of understanding it, we can learn much from the approaches adopted by researchers facing similar challenges on our own planet. Just as archaeologists reconstruct distant civilizations from fragments of evidence, SETI researchers aspire to reconstruct civilizations that are separated from us by vast expanses of space and time. Similarly, just as anthropologists seek to understand other cultures despite linguistic barriers and differences in social customs, as we attempt to decipher and interpret alien messages, we will be compelled to understand the thought processes of a species that is fundamentally different.”
On page 272, Vakoch discusses the feasibility of establishing symbolic/linguistic communication with extraterrestrial intelligence (ETI). He draws instructive parallels with human experience that continue to challenge us. One of these examples is “rock art,” which involves patterns or forms carved into stones millennia ago.
These ancient stone carvings are found in various countries, and the example shown above comes from Doddington Moor, Northumbria, England. Little or nothing can be said about the meaning, reason for their carving, or their authorship. Effectively, they could have been created by extraterrestrial beings. Unless we find a comprehensible interpretation of these patterns from the time they were created, we will never be able to definitively state what these patterns represent.