Magnetic field of the Moon


Magnetic field of the Moon
Total magnetic field strength at the surface of the Moon as derived from the Lunar Prospector electron reflectometer experiment.

The external magnetic field of the Moon is very weak in comparison to that of the Earth. Other major differences are that the Moon does not currently have a dipolar magnetic field (as would be generated by a geodynamo in its core) and the varying magnetization that is present is almost entirely crustal in origin. One hypothesis holds that the crustal magnetizations were acquired early in lunar history when a geodynamo was still operating. The small size of the lunar core, however, is a potential obstacle to this theory. Alternatively, it is possible that on an airless body such as the Moon, transient magnetic fields could be generated during large impact events. In support of this, it has been noted that the largest crustal magnetizations appear to be located near the antipodes of the giant impact basins. It has been proposed that such a phenomenon could result from the free expansion of an impact-generated plasma cloud around the Moon in the presence of an ambient magnetic field.[1]

Roughly once every moon orbit, the Moon passes through Earth's magnetotail for approximately 6 days. Interaction with the plasma sheet causes the Moon's surface to become negatively charged. On the Moon's dayside this effect is counteracted to a degree by sunlight: ultraviolet photons knock electrons back off the surface, keeping the build-up of charge at relatively low levels. But on the nightside electrons accumulate and surface voltages can climb to hundreds or thousands of volts.

There's growing evidence that fine particles of moondust might actually float, ejected from the lunar surface by electrostatic repulsion. This could create a temporary nighttime "atmosphere" of dust. The moondust atmosphere might also gather itself into a sort of diaphanous wind. Drawn by differences in global charge accumulation, floating dust would naturally fly from the strongly negative nightside to the weakly negative dayside. This "dust storm" effect would be strongest at the Moon's terminator. Much of these details are still speculative, but the Lunar Prospector spacecraft detected changes in the lunar nightside voltage during magnetotail crossings, jumping from -200 V to -1000 V. The plasma sheet is a very dynamic structure, in a constant state of motion, so as the Moon orbits through the magnetotail the plasma sheet can sweep across it many times with encounters lasting anywhere from minutes to hours or even days.[2]

The Chandrayaan-1 spacecraft mapped a "mini-magnetosphere" at the Crisium antipode on the moon's far side, using its Sub-keV Atom Reflecting Analyzer (SARA) instrument. The mini-magnetosphere is 360 km across at the surface and is surrounded by a 300-km-thick region of enhanced plasma flux that results from the solar wind flowing around the mini-magnetosphere.[3]

See also

References

  1. ^ Hood, L. L., and Z. Huang, L. L.; Huang, Z. (1991). "Formation of magnetic anomalies antipodal to lunar impact basins: Two-dimensional model calculations". J. Geophys. Res. 96: 9837–9846. Bibcode 1991JGR....96.9837H. doi:10.1029/91JB00308. 
  2. ^ NASA - The Moon and the Magnetotail
  3. ^ M. Wieser, et al. (2010), First observation of a mini‐magnetosphere above a lunar magnetic anomaly using energetic neutral atoms, Geophys. Res. Lett., 37, L05103, doi:10.1029/2009GL041721.

Wikimedia Foundation. 2010.

Look at other dictionaries:

  • Near side of the Moon — The names of the major seas and some craters on the near side of the Moon The near side of the Moon is the lunar hemisphere that is permanently turned towards the Earth, whereas the opposite side is the far side of the Moon. Only one side of the… …   Wikipedia

  • Gravitation of the Moon — 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… …   Wikipedia

  • Topography of the Moon — The topography of the Moon has been measured by the methods of laser altimetry and stereo image analysis, most recently from data obtained during the Clementine mission. The most visible topographic feature is the giant far side South Pole Aitken …   Wikipedia

  • Colonization of the Moon — Lunar outpost redirects here. For NASA s plan to construct an outpost between 2012 and 2024, see Lunar outpost (NASA). Moonbase redirects here. For other uses, see Moonbase (disambiguation). 1986 artist concept The colonization of the Moon is the …   Wikipedia

  • Earth's magnetic field — Computer simulation of the Earth s field in a normal period between reversals.[1] The tubes represent magnetic field lines, blue when the field points towards the center and yellow when away. The rotation axis of the Earth is centered and… …   Wikipedia

  • Geology of the Moon — The geology of the Moon (sometimes called selenology, although the latter term can refer more generally to lunar science ) is quite different from that of the Earth. The Moon lacks a significant atmosphere and any bodies of water, which… …   Wikipedia

  • Mercury's magnetic field — Magnetosphere of Mercury Graph showing relative strength of Mercury s magnetic field. Discovery[1] …   Wikipedia

  • Observing the Moon — The waxing gibbous Moon as observed from Earth The Moon is Earth s largest natural satellite and the nearest major celestial object. Observing the Moon can be accomplished by using a variety of instruments ranging from the naked eye to large… …   Wikipedia

  • Atmosphere of the Moon — The atmosphere of the Moon is very tenuous and insignificant in comparison with that of the Earth. One source of the lunar atmosphere is outgassing: the release of gases such as radon that originate from radioactive decay within the crust and… …   Wikipedia

  • Exploration of the Moon — Apollo 12 lunar module Intrepid prepares to descend towards the surface of the Moon. NASA photo. The physical exploration of the Moon began when Luna 2, a space probe launched by the Soviet Union, made an impact on the surface of the Moon on …   Wikipedia