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"page_type": "Visualization",
"title": "GRAIL Free-Air Gravity Map for the Cover of Science",
"description": "These print-resolution stills were created for the cover of the February 8, 2013 issue of Science. They show the free-air gravity map developed by the Gravity Recovery and Interior Laboratory (GRAIL) mission.If the Moon were a perfectly smooth sphere of uniform density, the gravity map would be a single, featureless color, indicating that the force of gravity at a given elevation was the same everywhere. But like other rocky bodies in the solar system, including Earth, the Moon has both a bumpy surface and a lumpy interior. Spacecraft in orbit around the Moon experience slight variations in gravity caused by both of these irregularities.The free-air gravity map shows deviations from the mean, the gravity that a cueball Moon would have. The deviations are measured in milliGals, a unit of acceleration. On the map, dark purple is at the low end of the range, at around -400 mGals, and red is at the high end near +400 mGals. Yellow denotes the mean.These views show a part of the Moon's surface that's never visible from Earth. They are centered on lunar coordinates 29°N 142°E. The large, multi-ringed impact feature near the center is Mare Moscoviense. The crater Mendeleev is south of this. The digital elevation model for the terrain is from the Lunar Reconnaissance Orbiter laser altimeter (LOLA). Merely for plausibility, the sun angle and starry background are accurate for specific dates (December 21, 2012, 0:00 UT and January 8, 2013, 14:00 UT, respectively). || ",
"release_date": "2013-02-08T00:00:00-05:00",
"update_date": "2025-01-05T22:20:25.616825-05:00",
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"description": "These print-resolution stills were created for the cover of the February 8, 2013 issue of Science. They show the free-air gravity map developed by the Gravity Recovery and Interior Laboratory (GRAIL) mission.
If the Moon were a perfectly smooth sphere of uniform density, the gravity map would be a single, featureless color, indicating that the force of gravity at a given elevation was the same everywhere. But like other rocky bodies in the solar system, including Earth, the Moon has both a bumpy surface and a lumpy interior. Spacecraft in orbit around the Moon experience slight variations in gravity caused by both of these irregularities.
The free-air gravity map shows deviations from the mean, the gravity that a cueball Moon would have. The deviations are measured in milliGals, a unit of acceleration. On the map, dark purple is at the low end of the range, at around -400 mGals, and red is at the high end near +400 mGals. Yellow denotes the mean.
These views show a part of the Moon's surface that's never visible from Earth. They are centered on lunar coordinates 29°N 142°E. The large, multi-ringed impact feature near the center is Mare Moscoviense. The crater Mendeleev is south of this. The digital elevation model for the terrain is from the Lunar Reconnaissance Orbiter laser altimeter (LOLA). Merely for plausibility, the sun angle and starry background are accurate for specific dates (December 21, 2012, 0:00 UT and January 8, 2013, 14:00 UT, respectively).",
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},
{
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"url": "http://archive.eso.org/ASTROM/",
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},
{
"name": "Catalog",
"common_name": "UCAC3",
"platform": "U.S. Naval Observatory",
"sensor": "Third CCD Astrograph",
"type": "Database",
"organizations": [
"USNO"
],
"description": "",
"credit": "",
"url": "",
"date_range": null
},
{
"name": "Free-Air Gravity",
"common_name": "GRAIL Free-Air Gravity",
"platform": "GRAIL",
"sensor": "Lunar Gravity Ranging System",
"type": "Analysis",
"organizations": [
"NASA"
],
"description": "",
"credit": "",
"url": "",
"date_range": "2012"
}
],
"nasa_science_categories": [
"Planets & Moons"
],
"keywords": [
"GRAIL",
"Gravity",
"Gravity Recovery and Interior Laboratory",
"Hyperwall",
"Lunar",
"Lunar Elevation Map",
"Lunar Topography",
"Moon",
"Satellites"
],
"recommended_pages": [],
"related": [
{
"id": 4014,
"url": "https://svs.gsfc.nasa.gov/4014/",
"page_type": "Visualization",
"title": "GRAIL Primary Mission Gravity Maps (AGU 2012)",
"description": "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. || ",
"release_date": "2012-12-05T12:00:00-05:00",
"update_date": "2017-01-23T12:22:42-05:00",
"main_image": {
"id": 470169,
"url": "https://svs.gsfc.nasa.gov/vis/a000000/a004000/a004014/topo_free.0200_preview.jpg",
"filename": "topo_free.0200_preview.jpg",
"media_type": "Image",
"alt_text": "Side-by-side rotating Moon globes showing LOLA elevation and GRAIL free-air gravity.This video is also available on our YouTube channel.",
"width": 1920,
"height": 1080,
"pixels": 2073600
}
}
],
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}