A gravity map is a map that depicts

gravity In physics, gravity (), also known as gravitation or a gravitational interaction, is a fundamental interaction, a mutual attraction between all massive particles. On Earth, gravity takes a slightly different meaning: the observed force b ...

measurements across an area of space, which are typically obtained via

gravimetry Gravimetry is the measurement of the strength of a gravitational field. Gravimetry may be used when either the magnitude of a gravitational field or the properties of matter responsible for its creation are of interest. The study of gravity c ...

. Gravity maps are an extension of the field of

geodynamics Geodynamics is a subfield of geophysics dealing with dynamics of the Earth. It applies physics, chemistry and mathematics to the understanding of how mantle convection leads to plate tectonics and geologic phenomena such as seafloor spreading, ...

. Readings are typically taken at regular intervals for surface analysis on

Earth Earth is the third planet from the Sun and the only astronomical object known to Planetary habitability, harbor life. This is enabled by Earth being an ocean world, the only one in the Solar System sustaining liquid surface water. Almost all ...

. Other methods include analysis of

artificial satellite A satellite or an artificial satellite is an object, typically a spacecraft, placed into orbit around a celestial body. They have a variety of uses, including communication relay, weather forecasting, navigation ( GPS), broadcasting, scienti ...

orbital mechanics Orbital mechanics or astrodynamics is the application of ballistics and celestial mechanics to rockets, satellites, and other spacecraft. The motion of these objects is usually calculated from Newton's laws of motion and the law of universal ...

, which can allow comprehensive gravity maps of planets, as has been done for

Mars Mars is the fourth planet from the Sun. It is also known as the "Red Planet", because of its orange-red appearance. Mars is a desert-like rocky planet with a tenuous carbon dioxide () atmosphere. At the average surface level the atmosph ...

NASA The National Aeronautics and Space Administration (NASA ) is an independent agencies of the United States government, independent agency of the federal government of the United States, US federal government responsible for the United States ...

. Gravity maps typically are based on depictions of gravity anomalies or a planet's

geoid The geoid ( ) is the shape that the ocean surface would take under the influence of the gravity of Earth, including gravitational attraction and Earth's rotation, if other influences such as winds and tides were absent. This surface is exte ...

Creation of gravity maps

Measurements are typically taken via measuring ground stations with surveys conducted at regular intervals. For surface mapping of gravity, placement of instruments can be randomized. Surface gravity mapping is often used to map out gravity anomalies such as a Bouguer anomaly or isostatic gravity anomalies. Derivative gravity maps are an extension of standard gravity maps, involving mathematical analysis of the local

gravitational field In physics, a gravitational field or gravitational acceleration field is a vector field used to explain the influences that a body extends into the space around itself. A gravitational field is used to explain gravitational phenomena, such as ...

strength, to present data in analogous formats to a

geological map A geological map or geologic map is a special-purpose map made to show various geological features. Rock (geology), Rock units or stratum, geologic strata are shown by color or symbols. Bed (geology), Bedding planes and structural features such ...

. Gravity maps, in a "heat" context, typically represent intensity being representative of concentrations of

mass Mass is an Intrinsic and extrinsic properties, intrinsic property of a physical body, body. It was traditionally believed to be related to the physical quantity, quantity of matter in a body, until the discovery of the atom and particle physi ...

in a given area, which correlates to that area having a stronger gravitational field; an example would be a

mountain range A mountain range or hill range is a series of mountains or hills arranged in a line and connected by high ground. A mountain system or mountain belt is a group of mountain ranges with similarity in form, structure, and alignment that have aris ...

. In the inverse, geological structures such as

oceanic trenches Oceanic trenches are prominent, long, narrow topographic depressions of the ocean floor. They are typically wide and below the level of the surrounding oceanic floor, but can be thousands of kilometers in length. There are about of oceanic t ...

or landmass depressions such as those caused by

glaciers A glacier (; or ) is a persistent body of dense ice, a form of rock, that is constantly moving downhill under its own weight. A glacier forms where the accumulation of snow exceeds its ablation over many years, often centuries. It acquires ...

fault lines In geology, a fault is a planar fracture or discontinuity in a volume of rock across which there has been significant displacement as a result of rock-mass movements. Large faults within Earth's crust result from the action of plate tectonic f ...

will depict lower gravitational field values, due to the lower underlying amount of mass in the area. Other methods include analysis of satellite orbital mechanics, which can allow comprehensive gravity maps of planets, as has been done for

. Goddard Mars Model (GMM) 3 is a gravity map of the gravitational field on the planet Mars. Three orbital craft over Mars, the

Mars Global Surveyor ''Mars Global Surveyor'' (MGS) was an American Robotic spacecraft, robotic space probe developed by NASA's Jet Propulsion Laboratory. It launched November 1996 and collected data from 1997 to 2006. MGS was a global mapping mission that examined ...

(MGS),

Mars Odyssey ''2001 Mars Odyssey'' is a robotic spacecraft orbiting the planet Mars. The project was developed by NASA, and contracted out to Lockheed Martin, with an expected cost for the entire mission of US$297 million. Its mission is to use spectro ...

(ODY), and the

Mars Reconnaissance Orbiter The ''Mars Reconnaissance Orbiter'' (''MRO'') is a spacecraft designed to search for the existence of water on Mars and provide support for missions to Mars, as part of NASA's Mars Exploration Program. It was launched from Cape Canaveral on Au ...

(MRO) assisted in the creation of the GMM 3 by the study of their orbital flight paths. Their travel times and the

Doppler shift The Doppler effect (also Doppler shift) is the change in the frequency of a wave in relation to an observer who is moving relative to the source of the wave. The ''Doppler effect'' is named after the physicist Christian Doppler, who described t ...

of radio communications between the respective craft and

parabolic antenna A parabolic antenna is an antenna that uses a parabolic reflector, a curved surface with the cross-sectional shape of a parabola, to direct the radio waves. The most common form is shaped like a dish and is popularly called a dish antenna or p ...

s belonging to the

Deep Space Network The NASA Deep Space Network (DSN) is a worldwide Telecommunications network, network of spacecraft communication ground segment facilities, located in the United States (California), Spain (Madrid), and Australia (Canberra), that supports NASA' ...

, and incremental variations of the communication timing of radio signals and travel times of the craft allowed for the creation of an accurate GMM 3. The Martian gravity map was generated using more than sixteen years of data.

External links

World Gravity Map Project (WGM)

References

{{Reflist, 1, refs= {{Cite web, date=October 1997, title=FS-239-95, Introduction to Potential Fields: Gravity, last1=Wellerstein, first1=Alex , url=https://pubs.usgs.gov/fs/fs-0239-95/fs-0239-95.pdf, access-date=2024-09-02, url-status=live, website=

United States Geological Survey The United States Geological Survey (USGS), founded as the Geological Survey, is an agency of the U.S. Department of the Interior whose work spans the disciplines of biology, geography, geology, and hydrology. The agency was founded on Mar ...

, archive-url=https://web.archive.org/web/20240415011119/https://pubs.usgs.gov/fs/fs-0239-95/fs-0239-95.pdf, archive-date=2024-04-15 4 {{Cite web, date=2016-04-05, title=GMM-3 Mars Gravity Map - Goddard Mars Model 3 map of the gravity field of Mars , url=https://datarepository.wolframcloud.com/resources/GMM3-Mars-Gravity-Map , url-status=live, website=

Wolfram Research Wolfram Research, Inc. ( ) is an American Multinational corporation, multinational company that creates computational technology. Wolfram's flagship product is the technical computing program Wolfram Mathematica, first released on June 23, 1988. ...

; Wolfram Data Repository, archive-url=https://web.archive.org/web/20240807065358/https://datarepository.wolframcloud.com/resources/GMM3-Mars-Gravity-Map, archive-date=2024-08-07 {{Cite web, date=2016-03-16, title=New Gravity Map Gives Best View Yet Inside Mars , last1=Steigerwald, first1=William, url=https://www.nasa.gov/missions/new-gravity-map-gives-best-view-yet-inside-mars/ , url-status=live, website=

, archive-url=https://web.archive.org/web/20240615025412/https://www.nasa.gov/missions/new-gravity-map-gives-best-view-yet-inside-mars/, archive-date=2024-06-15 {{Cite web, date=2004-03-30, title=Gravity Recovery And Climate Experiment (GRACE); Gravity Anomaly Maps and The Geoid , url=https://earthobservatory.nasa.gov/features/GRACE/page3.php, url-status=live, website=

NASA Earth Observatory NASA Earth Observatory is an online publishing outlet for NASA which was created in 1999. It is the principal source of satellite imagery and other scientific information about the climate and the environment which are being provided by NASA for ...

, archive-url=https://web.archive.org/web/20240313090810/https://earthobservatory.nasa.gov/features/GRACE/page3.php, archive-date=2024-03-13 Geophysics Gravimetry