Hollow Moon
The Hollow Moon theory is a pseudoscientific hypothesis proposing that Earth's Moon is either wholly hollow or otherwise contains a substantial interior space. No scientific evidence exists to support the idea.
The concept is related to or derived from the better-known Hollow Earth theory, and was an infrequent but recurring plot device in pre-spaceflight science fiction.
Two versions
The Hollow Moon theory never gained enough popularity for any major quasi-scientific hypothesis attempting to rationalize it to become notable. Modern Hollow Moon adherents can however be broadly grouped in two major camps:
- the Moon's formation process produced a hollow sphere through natural means. Details vary widely; the proposed mechanism is usually an undefined or pseudoscentific factor in accretion-disk dynamics. Some proponents of this view maintain that the Moon is not exceptional, but that all planetary bodies are hollow.
- the Moon's hollowness stems from its being an artifact. This view (the "Spaceship Moon Theory") usually correlates with other beliefs such as UFOs or ancient astronauts.
The scientific community considers both sub-theories to be entirely unsupported by evidence.
Scientific perspective
Mainstream scientific opinion on the internal structure of the Moon overwhelmingly supports a solid internal structure with a thin crust, an extensive mantle and a small denser core.[1][2] This is based on:
- Seismic observations. Besides Earth, the Moon is the only planetary body with a seismic observation network in place. Analysis of lunar seismic data have helped constrain the thickness of the crust (~45 km)[3] and mantle, as well as the core radius (~350 km).[4][5]
- Moment of inertia parameters. For the Moon, moment of inertia parameters have demonstrated that the core is ~1.4% of the total mass.[6] One such parameter, the normalized polar moment of inertia, is 0.393+/-0.001.[6][7] This is very close to the value for a solid object with radially constant density, which would be 0.4 (for comparison, Earth's value is 0.33). The normalized polar moment of inertia for a hollow Moon would have a higher value, closer to 0.67. 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.
- Fine-scale variation (e.g., variation along the orbit of the Lunar Prospector orbiter) of the lunar gravitational field, which is consistent with geologic processes involving a crust, mantle, and core.[6]
The large-scale gravitational field of the Moon, however, is unaffected by the internal distribution of mass if the internal density is assumed to vary only 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[8] lunar radius. This can be derived directly for a spherically symmetric Moon by applying the integral form[9] of Gauss's law. Therefore, the large-scale gravitational field of the Moon does not convey any information about the internal radial distribution of mass. Hollow Moon proponents would, however, have to account for the incredible density of the Moon's crust if it were in fact hollow. As gravitational pull is determined by mass, a hollow moon would require an inordinately dense crust to achieve observed gravitational values.
In literature
- In H.G. Wells's book The First Men in The Moon (1901), Wells describes the insect-like "Selenites" who live inside a hollow Moon.
- Edgar Rice Burroughs wrote an adventure novel, The Moon Maid (1922), set in the interior of a postulated hollow Moon which had an atmosphere and was inhabited. In the sequel, The Moon Men, natives of the hollow Moon invade and conquer Earth. Burroughs also wrote the Pellucidar series, set in the interior of a hollow Earth.
- That Hideous Strength (1945) by C.S. Lewis takes place on Earth, but a hollow Moon is an important part of the novel's background, and is known by its inhabitants as "Sulva."
- The Lomokome Papers, Herman Wouk's little-known venture into science fiction (1947),[10] also uses the concept.
- Neznaika on the Moon, (1965), by Russian author Nikolay Nosov.
References
- ^ Measurements of the lunar induced magnetic moment in the geomagnetic tail: Evidence for a lunar core?
- ^ BASA Research: Moon has Earth-like core
- ^ Khan, A. (2002). "An inquiry into the lunar interior: A nonlinear inversion of the Apollo lunar seismic data". Journal of Geophysical Research 107 (E6): 5036. Bibcode 2002JGRE..107.5036K. doi:10.1029/2001JE001658. ISSN 0148-0227.
- ^ Khan, A.; J. A. D. Connolly, J. Maclennan, K. Mosegaard (2007). "Joint inversion of seismic and gravity data for lunar composition and thermal state". Geophysical Journal International 168 (1): 243–258. doi:10.1111/j.1365-246X.2006.03200.x. ISSN 0956540X.
- ^ Nakamura, Y.; D. Lammlein, G. Latham, M. Ewing, J. Dorman, F. Press, N. Toksoz (1973). "New Seismic Data on the State of the Deep Lunar Interior". Science 181 (4094): 49–51. doi:10.1126/science.181.4094.49. ISSN 0036-8075. PMID 17769823. http://www.sciencemag.org/cgi/content/abstract/181/4094/49.
- ^ a b c Konopliv, A. S.; Binder, AB; Hood, LL; Kucinskas, AB; Sjogren, WL; Williams, JG (1998). "Improved Gravity Field of the Moon from Lunar Prospector". Science 281 (5382): 1476–1480. doi:10.1126/science.281.5382.1476. PMID 9727968.
- ^ NASA Moon Fact Sheet
- ^ Garrick-Bethell, I.; Wisdom, J; Zuber, MT (2006). "Evidence for a Past High-Eccentricity Lunar Orbit". Science 313 (5787): 652–655. doi:10.1126/science.1128237. ISSN 0036-8075. PMID 16888135.
- ^ Griffiths, David B. (1989). Introduction to electrodynamics. Englewood Cliffs, N.J: Prentice Hall. ISBN 0-13-481367-7. http://isbndb.com/d/book/introduction_to_electrodynamics_a01.html.
- ^ see Wouk - Lomokome Papers at epinions.com
See also