Editing Lunar Prospector (section)

=== Electron Reflectometer and Magnetometer (MAG/ER) ===
[[File:Lunar prospector instrument lp er fs lg.gif|thumb|''Lunar Prospector'' Electron Reflectometer (ER)]]
[[File:Lunar prospector instrument lp mag fs lg.gif|thumb|''Lunar Prospector'' Magnetometer (MAG)]]
[[File:Moon ER magnetic field.jpg|thumb|Total magnetic field strength at the surface of the Moon, derived from the electron reflectometer experiment.]]
The Magnetometer and Electron Reflectometer (collectively, MAG/ER) detected anomalous surface magnetic fields on the Moon, which are in stark contrast to a global [[magnetosphere]] (which the Moon lacks). the Moon's overall magnetic field is too weak to deflect the [[solar wind]], but MAG/ER discovered a small surface anomaly that can do so. This anomaly, about {{convert|100|km|abbr=on}} in diameter, has therefore been referred to as "the smallest known magnetosphere, [[magnetosheath]] and [[bow shock]] system in the Solar System."<ref>{{cite web |title=Magnetometer / Electron Reflectometer results |url=http://lunar.arc.nasa.gov/results/magelres.htm |publisher=NASA |access-date=July 14, 2008 |url-status=dead |archive-url=https://web.archive.org/web/20100527121330/http://lunar.arc.nasa.gov/results/magelres.htm |archive-date=May 27, 2010 }}</ref> Due to this and other magnetic features of the Moon's surface, hydrogen deposited by [[solar wind]] is non-uniformly distributed, being denser at the periphery of the magnetic features. Since hydrogen density is a desirable characteristic for hypothetical lunar bases, this information may be useful in choosing optimal sites for possible long-term Moon missions.

The electron reflectometer (ER) and [[magnetometer]] (MAG) were designed to collect information on the lunar [[magnetic field]]s. the Moon has no global magnetic field, but it does have weak localized magnetic fields at its surface. These may be paleomagnetic remnants of a former global magnetic field, or may be due to [[meteor]] impacts or other local phenomena. This experiment was to help map these fields and provide information on their origins, allow possible examination of distribution of [[mineral]]s on the lunar surface, aid in a determination of the size and composition of the lunar core, and provide information on the lunar induced magnetic [[dipole]].

The ER determined the location and strength of magnetic fields from the [[energy spectrum]] and direction of [[electron]]s. The instrument measured the pitch [[angle]]s of [[solar wind]] electrons reflected from the Moon by lunar magnetic fields. Stronger local magnetic fields can reflect electrons with larger pitch angles.  [[Field strength]]s as small as 0.01 [[nanotesla|nT]] could be measured with a spatial accuracy of about {{convert|3|km|abbr=on}} at the lunar surface. The MAG was a triaxial fluxgate magnetometer similar in design to the instrument used on [[Mars Global Surveyor]]. It could measure the magnetic field [[amplitude]] and direction at spacecraft altitude with a spatial resolution of about {{convert|100|km|abbr=on}} when ambient [[Plasma (physics)|plasma]] disturbances are minimal.

The ER and the electronics package were located at the end of one of the three radial science booms on ''Lunar Prospector''. The MAG was in turn extended further on a {{convert|0.8|m|abbr=on}} boom&mdash;a combined {{convert|2.6|m|abbr=on}} from ''Lunar Prospector'' in order to isolate it from spacecraft generated magnetic fields. The ER and MAG instruments had a combined mass of {{convert|5|kg|abbr=on}} and used 4.5 [[watt]]s of power.