Aliens might be living among us, according to a study by Harvard academics.

A new paper suggests extraterrestrials could also be living underground or in a base inside the Moon.

The study by Harvard University’s Human Flourishing program further puts forward the idea that UFOs, or unidentified aerial phenomena (UAP), may be spaceships visiting their Earth-based alien friends.

The researchers have investigated so-called ‘cryptoterrestrials’.

These could be disguising themselves as humans to fit in, may have come from Earth’s future or might have descended from intelligent dinosaurs.

The study was created to offer an alternate “unconventional” explanation for UAP sightings and to hypothesize what they might mean, and “the possibility that UAP may involve forms of non-human intelligence (NHI) that are already present in Earth’s environment in some sense” that exist “alongside us in distinct stealth”.

The paper reads: “The author became increasingly aware of the depth of evidence and theory that also tentatively supports another ultraterrestrial explanation: the “cryptoterrestrial” hypothesis (CTH) – our focus here – which holds that UAP may reflect activities of NHIs concealed here on Earth (e.g., underground) and its environs.”

Four theories on aliens living near humans are investigated.

The first are human cryptoterrestrials: A technologically advanced ancient human civilisation that was largely destroyed long ago (e.g. by flood), but continued to exist in remnant form.

The second are hominid or theropod cryptoterrestrials: A technologically advanced non-human civilisation consisting of some terrestrial animal which evolved to live in stealth (e.g., underground). The paper suggests these could be an ape-like hominid descendant, or descendants of “unknown, intelligent dinosaurs”.

The third cryptoterrestrials are former extraterrestrial or extratempestrial cryptoterrestrials. These would have arrived on Earth from elsewhere in the cosmos or from the human future, respectively, and concealed themselves in stealth, such as in the Moon.

Theory four, dubbed CTH 4, are “magical Cryptoterrestrials”: Entities which are less like homegrown aliens and more like “earthbound angels”.

The paper says these relate to the world inhabited by humans in ways that are less technological than magical, giving the examples of “fairies, elves, nymphs”.

The academics do conclude that their theories, especially the elves suggestion, might be hard to take by many people.

They add: “The principal weakness of CTH 4, by contrast, is its utter strangeness, particularly for readers schooled to limit themselves to modes of explanation within the bounds of, say, the standard model of physics.

“While belief in extraterrestrials is tenable, belief in (something like) fairies is simply not a live option for many scientists.”

The paper, “The cryptoterrestrial hypothesis: A case for scientific openness to a concealed earthly explanation for Unidentified Anomalous Phenomena” is not yet peer-reviewed.