Reiner Gamma

Reiner Gamma (γ) is an albedo feature that is located on the Oceanus Procellarum, to the west of the crater Reiner on the Moon. The center of the formation is located at selenographic coordinates Lunar coords and quad cat|7.5|N|59.0|W. It has an overall dimension of about 70 kilometres. The feature has a higher albedo than the relatively dark mare surface, with a diffuse appearance and a distinctive swirling, concentric oval shape. Related albedo features continue across the surface to the east and southwest, forming loop-like patterns over the "maria".

The Reiner Gamma feature is not associated with any particular irregularities in the surface, and so the cause was a mystery until similar features were discovered in Mare Ingenii and Mare Marginis on photographs taken by orbiting spacecraft. The feature on Mare Ingenii is located at the lunar opposite point from the center of Mare Imbrium. Likewise the feature on Mare Marginis is opposite the mid-point of Mare Orientale. Thus it is believed that the feature resulted from seismic energies generated by the impacts that created these maria. Unfortunately there is no such lunar mare formation located precisely on the opposite surface of the Moon, although the large crater Tsiolkovskiy lies within one crater diameter.

The central feature of the Reiner Gamma does bear a resemblance to the dipolar formation created by iron filings on a surface with a bar magnet on the underside. Low-orbiting spacecraft have observed a relatively strong magnetic field associated with each of these albedo markings. Some have speculated that this magnetic field and the patterns were created by cometary impacts. However the true cause remains uncertain.

The magnitude of the Reiner Gamma feature has a fieldstrength of approximately 15 nT, measured from an altitude of 28 km. This is one of the strongest localized magnetic anomalies on the Moon. [cite journal | author=N.C. Richmond, L.L. Hood, J.S. Halekas, D.L. Mitchell, R.P. Linn, M. Acuña | title=Correlation of a Strong Lunar Magnetic Anomaly with a High-Albedo Region of the Descartes Mountains | journal=Geophysical Research Letters | year=2003 | volume=30 | issue=7 | pages=48 | url=http://adsabs.harvard.edu/abs/2003GeoRL..30g..48R | accessdate =2006-06-27 | doi=10.1029/2003GL016938] The surface field strength of this feature may be sufficient to form a mini-magnetosphere, which could deflect the solar wind. As the particles in the solar wind are known to darken the lunar surface, the magnetic field at this site may account for the survival of this albedo feature. [cite conference | author=L. L. Hood, C. R. Williams | year=1989 | title=The Lunar Swirls - Distribution and Possible Origins | booktitle=Proceedings 19th Lunar and Planetary Science Conference | publisher=Cambridge University Press/Lunar and Planetary Institute | url=http://adsabs.harvard.edu/abs/1989LPSC...19...99H | accessdate =2006-06-27 ]

In early lunar maps by Francesco Grimaldi, this feature was incorrectly identified as a crater. His colleague Giovanni Riccioli then named it "Galilaeus", after Galileo Galilei. The name was later transferred northwest to the current crater Galilaei.

Notes and references

Other references

* Marvin W. Huddleston, " [http://www.geocities.com/kc5lei/SWIRL2001.htm Lunar Swirls, Magnetic Anomalies, and the Reiner Gamma Formation] ", 1994, Association of Lunar & Planetary Observers.
* Ewen A. Whitaker, "Mapping and Naming the Moon: A History of Lunar Cartography and Nomenclature", Cambridge University Press, 1999, ISBN 0-521-62248-4.

External links

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