UFOlogists have proposed that the moon, believed to be a natural satellite of Earth, is, in fact, a huge spaceship, a gigantic UFO, parked in orbit around the Earth by an advanced technological civilization.
The proposal that the moon is an artificial satellite of Earth, specifically an alien spaceship, a massive UFO, parked in orbit around the Earth, is known as the Spaceship Moon Theory, Artificial Moon Theory, or Alien Moon Theory.
According to proponents of the Spaceship Moon Theory in the UFO community, there is evidence to suggest that the moon was built by an alien civilization with science and technology much more developed than ours.
The Spaceship Moon Theory claims that the moon, as an alien UFO parked in orbit around the Earth, has a hollow inside. In other words, the moon is a hollowed-out artificial structure containing an underground base serving also as the interior of a gigantic UFO spaceship.
The startling hypothesis was first proposed in 1970 by two Russian scientists, members of the Soviet Academy of Science, Michael Vasin and Alexander Shcherbakov, in an article, "Is the Moon the Creation of Alien Intelligence?"
Vasin and Shcherbakov suggested that the moon was a natural space body converted into an artificial structure by alien engineers who melted the original solid core, deposited the molten lava on the lunar surface, and created an inner lunar space protected by an artificial shell below the outer shell we know as the lunar surface.
The alien race then placed their gigantic UFO in orbit around the Earth for reasons we can only speculate about.
Part of evidence that Vasin and Shcherbakov presented in support of the theory that the moon has an inner shell made of strong high-tensile engineering material was that lunar craters formed from impact of large space rocks are generally shallower than expected and that the bottoms of the craters tend to be flat or convex.
According to the theorists, this suggests that large meteors impacting on the lunar surface are unable to dig deeper because they hit an impenetrable inner shell made of a high-tensile material.
Vasin and Shcherbakov thus suggested that the moon consists of a natural rocky outer layer that is only about five miles thick and an inner shell that is up to 20 miles thick. Below the inner shell is a cavity that could contain an "atmosphere" to support alien life.
Other proponents of the hollowed-out Spaceship Moon Theory include Don Wilson, who published a book Our Mysterious Spaceship Moon in 1975, and George H. Leonard in his 1976 book, Someone Else is On the Moon.
One of the major reasons for believing the moon is hollow, according to Spaceship Moon theorists, is its calculated mean density of 3.3gm/cm3, compared with Earth's 5.5 gm/cm3.
Proponents of the Spaceship Moon Theory claim that the unexpectedly low mean density of the moon caused NASA Scientist Gordon MacDonald to remark, "[T]he data require that the interior of the Moon is more like a hollow than a homogeneous sphere."
MIT's Sean C. Solomon is also quoted as having written that "the Lunar Orbiter experiments vastly improved our knowledge of the Moon's gravitational field... indicating the frightening possibility that the Moon might be hollow."
An incident that Spaceship Moon theorists often cite as proof that the moon is hollow occurred on November 20, 1969, when the Apollo 12 crew conducted the Passive Seismic Experiment by crashing the Apollo 12 Lunar Module into the Moon. The impact created an artificial moonquake that caused the moon to reverberate "like a gong" for nearly an hour.
A similar observation was made during the Apollo 13 mission, with instruments recording reverberations that lasted for more than three hours, compared with a few minutes for the Earth, even in large earthquakes.
According to a NASA document relating to the 1970 Apollo 13 mission, "Nothing comparable happens when objects strike Earth."
"Back in November 1969, the Apollo 12 astronauts had sent their Lunar Module crashing into the Moon following their return to the command craft after the lunar landing mission. That Lunar Module struck with a force of one ton of TNT. The shock waves built up to a peak in eight minutes and continued for nearly an hour. The information from these two artificial moonquakes led to reconsideration of theories proposed about the lunar interior. Among puzzling features are the rapid build- up to the peak and the prolonged reverberations. Nothing comparable happens when objects strike Earth."
Spaceship Moon theorists claim that as a natural satellite, the moon is an outrageous anomaly, being obviously too big to have been captured naturally in the Earth's orbit, as Isaac Asimov acknowledged in his book Asimov on Astronomy, published in 1974.
The video below, produced by a Spaceship Moon theorist, lists some of the moon anomalies claimed to indicate that the moon is a gigantic alien spaceship.
The debate about the origin of the moon, supposedly a natural satellite of the Earth, continues to rage, and proponents of the Spaceship Moon theory point out that the seemingly intractable difficulties in accounting for the moon as a supposed natural satellite of the Earth point to its artificial, or more precisely, alien technological origin.
As far as UFOlogists are concerned, recent sightings of UFO fleets over the moon suggest there could be a massive underground hangar for spacecraft in the moon.
UFOlogists poring over Google Moon images claim regular discoveries of anomalies on the lunar surface that indicate that the moon has a hollow inside that serves as an alien base and interior of a giant UFO spaceship.
Below are examples of such images that UFOlogists believe debunk arguments by skeptics that moon anomalies in NASA images are only pixelation glitches.
UFOlogists have also held that the reason why NASA has not returned to the moon since the Apollo missions is that aliens are there.