Gravitation of the Moon

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Radial gravity anomaly at the surface of the Moon in Gal (acceleration)

The gravitational field of the Moon has been determined by the tracking of radio signals emitted by orbiting spacecraft. The principle used depends on the Doppler effect, whereby the line-of-sight spacecraft acceleration can be measured by small shifts in frequency of the radio signal, and the measurement of the distance from the spacecraft to a station on Earth. Since the gravitational field of the Moon affects the orbit of a spacecraft, it is possible to use these tracking data to invert for gravity anomalies. However, because of the Moon's synchronous rotation it is not possible to track spacecraft much over the limbs of the Moon, and the far-side gravity field is thus only poorly characterized. The acceleration due to gravity on the surface of the Moon is 1.6249 m/s2, about 16.6% that on Earth's surface.[1] Over the entire surface, the variation in gravitational acceleration is about 0.0253 m/s2 (1.6% of the acceleration due to gravity). Because weight is directly dependent upon gravitational acceleration, things on the Moon will weigh only 16.6% of what they weigh on the Earth.

Gravity acceleration at the surface of the Moon in m/s2. Near side on the left, far side on the right. Map from Lunar Gravity Model 2011.


The origin of mascons are in part due to the presence of dense mare basaltic lava flows that fill some of the impact basins.[3] However, lava flows by themselves cannot explain the entirety of the gravitational variations, and uplift of the crust-mantle interface is required as well. Based on Lunar Prospector gravitational models, it has been suggested that some mascons exist that do not show evidence for mare basaltic volcanism.[4] The huge expanse of mare basaltic volcanism associated with Oceanus Procellarum does not possess a positive gravity anomaly.

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  1. ^ C. Hirt and W. E. Featherstone (2012). "A 1.5 km-resolution gravity field model of the Moon". Earth and Planetary Science Letters. 329–330: 22–30. Bibcode:2012E&PSL.329...22H. doi:10.1016/j.epsl.2012.02.012. Retrieved 2012-08-21. 
  2. ^ P. Muller and W. Sjogren (1968). "Mascons: Lunar mass concentrations". Science 161 (3842): 680–684. Bibcode:1968Sci...161..680M. doi:10.1126/science.161.3842.680. PMID 17801458. 
  3. ^ Richard A. Kerr (12 April 2013). "The Mystery of Our Moon's Gravitational Bumps Solved?". Science 340: 128. 
  4. ^ A. Konopliv, S. Asmar, E. Carranza, W. Sjogren and D. Yuan (2001). "Recent gravity models as a result of the Lunar Prospector mission". Icarus 50: 1–18. Bibcode:2001Icar..150....1K. doi:10.1006/icar.2000.6573.