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As conspiracy theories go, believing that the Moon is hollow is up there
with thinking its made out of cheese. The Hollow Moon hypothesis suggests that the
moon might be the product of an alien civilisation and could be a giant spacecraft or space station.
However, as with all the best conspiracy theories, the idea is based on some elements of truth.
So lets see how Sci-fi storeys, misinterpreted information and the Apollo missions gave rise
to the hollow moon theory and why you should look a little further than just the headline.
We can trace the idea of the hollow moon hypothesis back to HG wells
and his 1901 novel The first men in the Moon. In it, a businessman moves to a small cottage
in the country only to discover that his neighbour has created a material which he calls calvorite,
which can negate the force of gravity. The two go on to use it to build a spacecraft to travel to
the moon. Here they discover a sophisticated extraterrestrial civilisation of insect-like
creatures they call "Selenites" who live under the surface of the moon.
Wells himself had borrowed the idea first raised by Edmond Halley in 1692 that the Earth may hollow
and the 1741 novel by Ludvig Holberg called Niels Klim's Underground Travels about a hollow earth.
In 1965, professor and author Isaac Asimov noted that it seemed remarkable that the
moon was a perfect fit to just cover the sun during a full solar eclipse and that
this sheer coincidence should only occur on the earth, and none of the other planets given all
the variables of the distance of the sun to the earth and the moon to the earth.
Later, Conspiracy theorists would use this as evidence that the moon was an artificial
object even though astronomers have pointed out that the angular diameters of Sun and Moon
vary over time by several per cent making eclipse’s not so perfect as once thought.
In 1965, astronomer Wallace Eckert attempted to calculate the lunar
moment of inertia factor using an unusual analysis of the Moon's perigee and node.
The moment of inertia is a number, ranging from 0 to 0.67, that represents the distribution
of mass in a spherical body. When Eckert did his calculations,
the result came back of that of a hollow body, something which he rejected as ridiculous. It
was later found that he had not taken into account the nonuniformity of Earth's rotation
in the orbital theory of the Moon. By 1968 other methods had calculated
the value to 0.394, very close to the value of a sphere with a equal distribution of mass of 0.4.
In 1970, Michael Vasin and Alexander Shcherbakov, of the Soviet Academy of Sciences suggested that
the moon could be a spacecraft built by unknown beings. They came to this idea because of the
shape of some of the large craters which are thought to be meteor impacts were too
shallow with flat or even convex bottoms whereas smaller impacts produce more of a cup-like crater.
They proposed that the larger impacts were shallow because they were going
down through the rocky surface and hitting the armoured hull of a giant spacecraft.
It was suggested that this was more likely an attempt by the atheist Soviet
Government to undermine the West’s faith in religion than a real scientific explanation.
So, It is with this background of conflicting or just inaccurate information that conspiracy
theorists would be drawn to when the Apollo moon landings started.
Putting a man on the moon might have been the highlight for the U.S. government to show the
world that democracy could outdo communism, but for NASA and thousands of scientists around the
world, they also wanted to find out more about the moon, what it was really made out of,
could it be made habitable and how had it formed. In order to find out more about the structure
of the moon all the Apollo missions carried seismographic measuring systems
which were part of the Apollo Lunar Surface Experiments Package or ALSEP.
On Apollo 11 they left behind the Passive Seismic Experiment or PSE
to record Seismic activity and meteor impacts and a magnetometer to measure
the moon’s magnetic field to see if it had a molten core like the earth.
The PSE was meant to work for about a year but failed just over 4 weeks later,
it was believed from overheating from the sunlight of the very long lunar day. During its operation,
it recorded between 100 - 200 seismic events which could have been moonquakes or meteor hits.
On Apollo 12, NASA sought to find out more by creating a large shock waves on the surface.
After the ascent module had returned the crew from the surface to the command module,
it was deliberately crashed into the surface of the moon with the equivalent explosive power
of about 1 ton of TNT to create shockwaves which could be picked up by the ALSEP seismic devices.
Moonquakes were an unexpected discovery from seismometers,
and the shockwaves from these were both larger and echoed around the moon for much
longer than was expected indicating that it was less dense than thought.
On Apollo 13, 14, 15, 16 and 17, the Saturn third stage which had to taken
the command model to the moon and was now exhausted was deliberately crashed into the
moons surface to create a moonquake. These were picked by all the seismic
detectors which had been left by the current and previous missions apart from Apollo 11 and 13.
The results which they sent back to NASA confirmed the moon’s lower density.
The seismic detectors continued to work up until 1977, when they were switched off by NASA five
years after the landing of the final Apollo 17. In that time they picked up more seismic activity
than was originally anticipated with some of the moonquakes measured upto 5.5 on the Richter scale.
It was found that there were four types of moonquakes. (1) deep moonquakes about 700 km
below the surface, (2) vibrations from the impact of meteorites; (3) thermal quakes caused by the
expansion of the supercooled crust when first illuminated by the morning sun after two weeks
of lunar night; and (4) shallow moonquakes only 20 or 30 kilometres below the surface.
In a 2005, Clive Neal, professor of civil engineering and geological sciences at the
University of Notre Dame was going over the data from 1970s to see how lunar habitats
would react to moonquakes and made a comment that was taken out of context and got the
conspiracy theorists all worked up again. In his paper he said that the first 3
types of moonquakes were quite mild but the shallow ones were the worst
and lasted much longer than they would on earth. Once they started, they just kept going, up to 10
minutes compared to about 2 minutes on earth. “The moon was ringing like a bell” he said, and this
was where some people took his words literally. If the moon was ring like a bell, then it must
be hollow like a bell and made of metal or some other non-rocky material they deduced.
The “ringing like a bell” metaphor meant that the vibrations lasted much longer like
the resonance of a bell or tuning fork. The reason for this is that the moon is
dry with very little water content compared to the earth. The water on
the earth has a weathering effect on rocks and expanding the structure of different minerals
When the shock waves from an earthquake hit these materials it acts like a shock
absorber dampening the energy and greatly reducing the ringing effect.
The moon, however, is dry, cool and mostly rigid, like a chunk of stone or iron. So
moonquakes set it vibrating like a tuning fork. Even if a moonquake isn't intense,
"it just keeps going and going," Neal says. And for a lunar habitat, that persistence could be
more significant than a moonquake's magnitude. This is where things just took on a life of
their own and conspiracy theories grow and mutate like Chinese whispers. The moon isn’t hollow but
it is less dense due to the smaller iron core. Rock samples containing stable-isotope ratios
of lunar and terrestrial rock are identical which shows that they have a common origin
and the moon is not a foreign or alien object or spacecraft from outside our solar system.
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