Hollow Moon

Schematic illustration showing a cross-section of the currently accepted internal structure of the Earth's Moon, as opposed to the "Hollow Moon" hypothesis.

The Hollow Moon hypothesis proposes that Earth's Moon is either wholly hollow or otherwise contains a substantial interior space. No scientific evidence exists to support the idea; seismic observations and other data collected since spacecraft began to orbit or land on the Moon indicate that it has a thin crust, extensive mantle and small, dense core, although overall it is much less dense than Earth.

The Hollow Moon concept is similar to the better-known Hollow Earth hypothesis, and was a recurring plot device in pre-spaceflight science fiction.

Hollow Moon adherents can be broadly grouped in two major camps, neither of which is considered by the scientific community to be supported by evidence:

Scientific perspective

A 2011 NASA press release, and a single 1976 scientific study on the internal structure of the Moon speculate on the possibility of a solid internal structure with a thin crust, an extensive mantle and a small denser core.[1][2] This is based on:

  1. 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]
  2. 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.
  3. 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.

Conflicting arguments

University of Notre Dame Professor of Civil Engineering and Geological Sciences Clive R. Neil described the Moon as "ringing like a bell," leading to arguments that it must be hollow like a bell. Lunar seismology experiments since then have shown that the lunar body has shallow "moonquakes" that act differently from quakes on Earth, due to differences in texture, type and density of the planetary strata, but no evidence of any large empty space inside the body.[10]

The Moon's density is 3.34 g/cm3 (3.34 times an equal volume of water) whereas the Earth's is 5.5. Proponents argue that this indicates the Moon must have a large cavity inside it.

Some proponents argue that lunar craters are too shallow to be easily explained. A recent study indicates that larger craters on the near side may be a reflection of the thickness of the crust.[11]

In literature

References

  1. ↑ Measurements of the lunar induced magnetic moment in the geomagnetic tail: Evidence for a lunar core?
  2. ↑ BASA Research: Moon has Earth-like core
  3. ↑ 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.
  4. ↑ 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. Bibcode:2007GeoJI.168..243K. doi:10.1111/j.1365-246X.2006.03200.x. ISSN 0956-540X.
  5. ↑ 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. Bibcode:1973Sci...181...49N. doi:10.1126/science.181.4094.49. ISSN 0036-8075. PMID 17769823.
  6. 1 2 3 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. Bibcode:1998Sci...281.1476K. doi:10.1126/science.281.5382.1476. PMID 9727968.
  7. ↑ NASA Moon Fact Sheet
  8. ↑ Garrick-Bethell, I.; Wisdom, J; Zuber, MT (2006). "Evidence for a Past High-Eccentricity Lunar Orbit". Science 313 (5787): 652–655. Bibcode:2006Sci...313..652G. doi:10.1126/science.1128237. ISSN 0036-8075. PMID 16888135.
  9. ↑ Griffiths, David B. (1989). Introduction to electrodynamics. Englewood Cliffs, N.J: Prentice Hall. ISBN 0-13-481367-7.
  10. ↑ NASA Science News: "Moonquakes"
  11. ↑ MIT: "Researchers find that huge craters on the near side of the moon may overstate the intensity of asteroid impacts about 4.1 billion years ago."
  12. ↑ see Wouk - Lomokome Papers at epinions.com
  13. ↑ Run (Awolnation album)

External links

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