A unit used to describe the change in the force of gravity as the observer moves horizontally along a planetary surface. 1 eötvös is a change of 10⁻⁹ gal per centimeter of horizontal distance. In other words, the eötvös is not a measure of the strength of gravity, but of the magnitude of the change as the observer moves from place to place. Symbol, E.

Because gravity is stronger at the Earth's poles than at the equator, on average movement along a north-south line produces around 5 E, ignoring local influences. Changes when the observer moves along an east-west line are entirely due to local influences. The largest observed change is about 50 E.

The unit was first proposed in 1929¹ and is named for the Hungarian physicist, Baron Roland von Eötvös (1848-1919).

images of an area on the moon

Courtesy NASA/JPL-Caltech/CSM.

Above is an example of the use of the eötvös. Both images are of the Crisium basin on the moon. The image on the right shows surface relief; colors indicate altitude. In the left image colors represent changes in the strength of gravity. Visible on that image is a linear feature where the force of gravity weakens; a dotted line on both images shows the location of this gravity anomaly. The anomaly, however, is not visible in the surface features. That the anomaly is not visible within the crater on the gravity map suggests that the anomaly is older than the basin, and that part of it was destroyed by the impact that formed the crater.

1. D. C. Barton.
Geophysical Prospecting.
New York: Institute of Mining and Metallurgical Engineering, 1929.

Page 421.

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