Hollow moon

The Hollow moon theory is a pseudoscientific theory that suggests that the Moon is a large hollow sphere. Little published evidence exists to support the idea.

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Seismometer recordings from November 1969 are often cited as evidence. After seismometers were set up on the Moon's surface by the astronauts of Apollo XII, astronauts heading back to Earth discarded the ascent stage of the lunar module, dropping it on the moon's surface. The craft smashed and the shock waves the seismometers picked up lasted for about an hour. Seismic activity recorded since then demonstrates the presence of a core^[1].

Further evidence against the theory exists in the Moon's moment of inertia, which has been measured .394^[2]. The moment of inertia of a solid sphere is 0.4. This strongly suggests that the Moon is not hollow and possesses a small denser core.^[3] Furthermore, fine-scale variation (e.g., variation along the orbit of the Lunar Prospector orbiter) of the lunar gravitational field is consistent with geologic processes involving a crust, mantle, and core. ^[4]

The only effective ways to determine the distribution of mass within a planetary body are:

1. Moment of inertia parameters. For the moon, moment of inertia parameters have demonstrated that the core is ~1.4% of the total mass.^[4] One such parameter, the normalized polar moment of inertia, is 0.393+/-0.001,^[4] which is very close to that for a solid object with radially constant density (for comparison, Earth's value is 0.33). In other words, the moment of inertia parameters indicate that the core of the moon is both dense and small, with the rest of the moon consisting of material with nearly-constant density.
2. Seismic observations. Besides Earth, the moon is the only planetary body with a seismic observation network in place as discussed above. The lunar seismic data have helped constrain the thickness of the crust (~45 km)^[5] and mantle, as well as the core radius (~350 km).^[6]

The gravitational field of the moon would be unaffected by the radial distribution of mass within the moon if the density of the moon only varied radially. For example, had the moon been replaced with a point object of identical mass, the current gravitational field would continue to exist at distances greater than the ~1700 km^[7] lunar radius. This can be derived directly for a spherically symmetric moon by applying the integral form ^[8] of Gauss's law. Therefore, the large-scale gravitational field of a planet does not convey any information about the (radial) distribution of mass. Nevertheless, if a hollow moon is assumed, the lunar density would have to be un-physically large to generate the observed gravitational field.

Hollow moons in literature

Science fiction author Edgar Rice Burroughs wrote an adventure novel, The Moon Maid, set in the interior of a postulated hollow moon, which in his conception had an atmosphere and was inhabited. In the sequel, The Moon Men, natives of the hollow moon invaded and conquered Earth. Burroughs also wrote the series of Pellucidar novels set in the interior of a hollow Earth.

H.G. Wells's book The First Men in The Moon and the films made on the basis of it are based on the idea.

The Lomokome Papers, Herman Wouk's little-known venture into Science Fiction (1947)^[9] also uses the concept.

That Hideous Strength by C.S. Lewis takes place on Earth, but an important part of its background is the hollow Moon, known by its inhabitants as "Sulva".

References

1. ^ http://www.sciencemag.org/cgi/content/abstract/181/4094/49
2. ^ http://nssdc.gsfc.nasa.gov/planetary/factsheet/moonfact.html
3. ^ http://www-ssc.igpp.ucla.edu/personnel/russell/papers/measure(9)/
4. ^ ^{a b c} Konopliv et al. (1998), doi 10.1126/science.281.5382.1476
5. ^ Khan et al. (2002), doi 10.1029/2001JE001658
6. ^ Khan et al. (2007), doi 10.1111/j.1365-246X.2006.03200.x
7. ^ Garrick-Bethell et al. (2006), doi 10.1126/science.1128237
8. ^ Griffiths (1989), ISBN 0134813677
9. ^ see Wouk - Lomokome Papers at epinions.com