GRAIL Primary Mission Gravity Maps (AGU 2012)
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- Visualizations by:
- Ernie Wright
- View full credits
The Gravity Recovery and Interior Laboratory (GRAIL) mission comprises a pair of satellites launched in September, 2011 and placed in orbit around the Moon in January, 2012. The two satellites, named Ebb and Flow, used radio signals to precisely measure their separation as they flew in formation, one following the other in the same nearly circular polar orbit. These measurements allowed mission scientists to build up an accurate and detailed gravity map of the Moon.
If the Moon were a perfectly smooth sphere of uniform density, the gravity experienced by the spacecraft would be exactly the same everywhere. But like other rocky bodies in the solar system, including the Earth, the Moon has both a bumpy surface and a lumpy interior. As the spacecraft fly in their orbits, they experience slight variations in gravity caused by both of these irregularities, variations which show up as small changes in the separation of the two spacecraft.
The free-air gravity map shows these variations directly. (Free-air
is a historical term; there is, of course, no air on the Moon.) The Bouguer gravity map subtracts the effect of the bumpy surface to show the lumpiness underneath. The elevation maps from the laser altimeter on Lunar Reconnaissance Orbiter (LRO) were used to create a model of what the gravity would be if the Moon were bumpy but not lumpy. This model was then subtracted from the free-air map to produce the Bouguer map. (Note: The Bouguer map shown here was filtered to emphasize smaller features; harmonic degrees 1 to 6 were excluded.)
The crustal thickness map is inferred from the Bouguer map: If the density of the crust is assumed to be uniform, then the gravity anomalies visible in the Bouguer gravity map can be explained by variations in the thickness of the crust. Highs in gravity indicate places where the denser mantle is closer to the surface, and hence where the crust is thinner.
While aiding navigation for future lunar missions, GRAIL's gravity measurements reveal information about the internal structure of the Moon, improving our understanding of the origin and development of not just the Moon, but also the Earth and the rest of the inner solar system.
Side-by-side rotating Moon globes showing LOLA elevation and GRAIL free-air gravity.
This video is also available on our YouTube channel.
Moon free-air gravity maps in a cylindrical projection suitable for spherical texture mapping. Centered at 0° longitude. Includes shaded relief of surface features. Versions of the map are provided which either include or omit lower harmonic degrees corresponding to large features in the gravity field.
Moon Bouguer gravity maps in a cylindrical projection suitable for spherical texture mapping. Centered at 0° longitude. Includes shaded relief of surface features. Versions of the map are provided which either include or omit lower harmonic degrees corresponding to large features in the gravity field.
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Credits
Please give credit for this item to:
NASA's Goddard Space Flight Center Scientific Visualization Studio
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Animator
- Ernie Wright (USRA) [Lead]
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Scientists
- Erwan M. Mazarico (NASA/GSFC)
- Maria Zuber (Massachusetts Institute of Technology)
Missions
This visualization is related to the following missions:Series
This visualization can be found in the following series:Papers used in this visualization
M. T. Zuber et al., Gravity field of the Moon from the Gravity Recovery and Interior Laboratory (GRAIL), Science 10.1126/science.1231507 (Dec. 5, 2012)
Datasets used in this visualization
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LRO DEM (Digital Elevation Map)
ID: 653 -
GRAIL GRAIL Free-Air Gravity (Free-Air Gravity)
ID: 766 -
GRAIL GRAIL Bouguer Gravity (Bouguer Gravity)
ID: 767 -
GRAIL GRAIL Crustal Thickness (Crustal Thickness)
ID: 768
Note: While we identify the data sets used in these visualizations, we do not store any further details, nor the data sets themselves on our site.
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