Crustal magnetism is the magnetic field of the crust of a planetary body. The crustal magnetism of Earth has been studied; in particular, various magnetic crustal anomalies have been studied. Two examples of crustal magnetic anomalies on Earth that have been studied in the Americas are the Brunswick magnetic anomaly (BMA) and East Coast magnetic anomaly (ECMA). Also, there can be a correlation between physical geological features and certain readings from crustal magnetism on Earth. Below the surface of the Earth, the crustal magnetism is lost because the temperature rises above the curie temperature of the materials producing the field. On Mars the crustal magnetic fields have been noted as affecting its ionosphere. (See also

Atmosphere of Mars The atmosphere of Mars is the layer of gases surrounding Mars. It is primarily composed of carbon dioxide (95%), molecular nitrogen (2.8%), and argon (2%). It also contains trace levels of water vapor, oxygen, carbon monoxide, hydrogen, and no ...

) The magnetic fields on Mars from its rocks and crust are thought to come from

ferromagnetism Ferromagnetism is a property of certain materials (such as iron) which results in a large observed magnetic permeability, and in many cases a large magnetic coercivity allowing the material to form a permanent magnet. Ferromagnetic materials ...

and if the material is heated above its

curie temperature In physics and materials science, the Curie temperature (''T''C), or Curie point, is the temperature above which certain materials lose their permanent magnetic properties, which can (in most cases) be replaced by induced magnetism. The Cur ...

the magnetic imprint is un-done. The

Mars Global Surveyor ''Mars Global Surveyor'' (MGS) was an American robotic space probe developed by NASA's Jet Propulsion Laboratory and launched November 1996. MGS was a global mapping mission that examined the entire planet, from the ionosphere down through the a ...

(MGS) discovered magnetic stripes in the crust of Mars, especially in the Phaethontis and

Eridania quadrangle The Eridania quadrangle is one of a series of 30 quadrangle maps of Mars used by the United States Geological Survey (USGS) Astrogeology Research Program. The Eridania quadrangle is also referred to as MC-29 (Mars Chart-29). The Eridania quadr ...

s (

Terra Cimmeria Terra Cimmeria is a large Martian region, centered at and covering at its broadest extent. It covers latitudes 15 N to 75 S and longitudes 170 to 260 W. It lies in the Eridania quadrangle. Terra Cimmeria is one part of the heavily cratered, s ...

and

Terra Sirenum Terra Sirenum is a large region in the southern hemisphere of the planet Mars. It is centered at and covers 3900 km at its broadest extent. It covers latitudes 10 to 70 South and longitudes 110 to 180 W. Terra Sirenum is an upland area nota ...

). The

magnetometer A magnetometer is a device that measures magnetic field or magnetic dipole moment. Different types of magnetometers measure the direction, strength, or relative change of a magnetic field at a particular location. A compass is one such device, o ...

on MGS discovered wide stripes of magnetized crust running roughly parallel for up to . These stripes alternate in polarity, with the north magnetic pole of one pointing up from the surface and the north magnetic pole of the next pointing down. When similar stripes were discovered on Earth in the 1960s, they were taken as evidence of

plate tectonics Plate tectonics (from the la, label=Late Latin, tectonicus, from the grc, τεκτονικός, lit=pertaining to building) is the generally accepted scientific theory that considers the Earth's lithosphere to comprise a number of large ...

. Researchers believe these magnetic stripes on Mars are evidence for a short, early period of plate tectonic activity. Only roughly half of Mars seems to have a crustal magnetic field; there are several possible explanations for this, such as that an internal dynamo only affected part of the planet, or that a body struck Mars in the past destroying the magnetism. Lunar crustal magnetism has also been discovered and studied. The

Lunar Prospector ''Lunar Prospector'' was the third mission selected by NASA for full development and construction as part of the Discovery Program. At a cost of $62.8 million, the 19-month mission was designed for a low polar orbit investigation of the Moon, ...

probe of the 1990s mapped the lunar crustal magnetic field across the whole globe of the Moon for the first time. This allowed the impact on magnetic fields of previously identified impact basins to be studied. tp://ftp.lpl.arizona.edu/pub/lpl/lon/moon/mitchell08ica.pdf The impact basins Orientale and Imbrium had some of the weakest magnetic fields in the survey, and additional study puts constraints on the existence of steady ambient lunar magnetic fields in the Moon's past given the assumptions of the data and collection techniques. Remnant crustal magnetic fields are studied on Moon as in this case, and have also been examined on Earth and on Mars. However, these are the only bodies that have by the early 21st century been studied, though it is predicted other bodies will have this geological feature.

References

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External links

* tp://ftp.lpl.arizona.edu/pub/lpl/lon/moon/mitchell08ica.pdf Global mapping of lunar crustal magnetic fields by Lunar Prospector D.L. Mitchell, et al.(2008)
Elements Magazine - Crustal Magnetism, Lamellar Magnetism and Rocks That Remember
Magnetism in astronomy Geomagnetism