A new research paper from a team at Harvard University and the University of Montana suggests that aliens have likely visited Earth—and could still be living among us in secret.

The peer-reviewed report more specifically argues that the scientific community should be open to the possibilities presented by Unidentified Anomalous Phenomena (UAP). The researchers explored the “cryptoterrestrial hypothesis,” a subset of a theory that UAP sightings may be activities of intelligent beings.

“UAP may reflect activities of intelligent beings concealed in stealth here on Earth (e.g., underground), and/or its near environs (e.g., the moon), and/or even ‘walking among us’ (e.g., passing as humans,” the authors explain.

“Fundamentally, UAP constitute an extraordinary empirical mystery, which science is surely obligated to investigate, yet has rarely done so—at least in an open, public, visible way,” the report adds.

UAP can appear in different forms, including strange lights in the sky or objects moving over or under the surface of Earth’s oceans. Most commonly, these events are labeled as Unidentified Aerial Phenomena (UAP)—or Unidentified Flying Objects (UFOs)—that witnesses describe as drones or even alien spaceships.

The report did not directly assert or deny the existence of extraterrestrial life but asked the scientific community to be open to the idea—including the possibility that aliens could be living in underground bases on Earth and the moon.

“Although this idea is likely to be regarded skeptically by most scientists, such are the nature of some UAP,” the researchers declared. “We argue this possibility should not be summarily dismissed, and instead deserves genuine consideration in a spirit of epistemic humility and openness.”

Their work was published in the open-access journal Philosophy and Cosmology, an international, double-blind peer-reviewed outlet of the International Society of Philosophy and Cosmology. The report was authored by Tim Lomas, Brendan Case, and Michael Masters, who did not respond to a request for comment from Decrypt.

A “double-blind” or “double anonymized” peer review is a process used by academic journals to ensure that articles are fairly reviewed by experts in the field while concealing the identity of both the authors and the reviewers, with only the editor knowing who they are.

The paper broke down four categories of the cryptoterrestrial hypothesis: Human cryptoterrestrials would be an advanced ancient human civilization, like the mythical Atlantis, destroyed in an apocalypse. Hominids and theropod cryptoterrestrials would be animals that evolved in stealth, as portrayed in movies and TV shows like Land of the Lost or more recently in Legendary Pictures’Monterverse. Former extraterrestrials, or extratemporal cryptoterrestrials, include aliens or future descendants who arrived on Earth via time travel, such as those depicted in the BBC television series Primeval. The final category is magical cryptoterrestrials, entities resembling earthbound or fallen angels that interact with humans in seemingly magical ways.

The possibility of extraterrestrial life on or around Earth ramped up in 2023 as the U.S. government released classified documents related to UAP sightings. Last year, during a congressional hearing before the House Oversight Subcommittee on National Security, witnesses who claim to have seen UAPs firsthand said they pose a serious national security threat.

"If UAPs are foreign drones, it's an urgent national security problem; if it's something else, it's an issue for science," executive director of Americans for Safe Aerospace Ryan Graves told the committee. "In either case, unidentified objects are a concern for flight safety, and the American people deserve to know what is happening in our skies."

For decades, the U.S. government has been accused of hiding the existence of alien life, to which Tennessee Rep. Tim Burchett said Congress has had enough.

“We’re done with the cover-ups,” he said.

In January, Congressman Robert Garcia (D-CA) and Congressman Glenn Grothman (R-WI) introduced the ‘Safe Airspace for Americans Act’ to make it easier for civilian pilots and personnel to report UAPs. On Tuesday, Garcia announced his proposed amendments to the National Defense Authorization Act were blocked in the House.

Despite witness testimony, the U.S. Department of Defense’s All-domain Anomaly Resolution Office (AARO) released a separate report in March regarding UAPs, concluding there was no evidence of visitors from the stars.

"AARO has found no verifiable evidence that any UAP sighting has represented extraterrestrial activity," AARO acting Director Tim Phillips said during a briefing at the Pentagon. "AARO has found no verifiable evidence that the U.S. government or private industry has ever had access to extraterrestrial technology. AARO has found no indications that any information was illegally or inappropriately withheld from Congress."

Edited by Ryan Ozawa.