| Summary: | A geophysical experiment was conducted in a 2-km-deep hole in the Greenland ice cap at depths between 213 m and 1673 m to test for possible violations of Newton's inverse-square law. A detailed ice-sounding radar survey was carried out to 5 km from the hole and merged with regional airborne radar data to define the basement interface. Highly accurate gravity measurements were carried out to 15 km from the hole to detect lateral density changes in the bedrock. The measurements were controlled with very accurate satellite and conventional positioning techniques. The basement interface model was input into a Newtonian computation to correct the observed gravity for known earth structure resulting in an anomalous gravity gradient of +3.87 mGal. A 3 dimensional ideal body analysis of the surface and borehole gravity data provided a means of bounding all possible Newtonian solutions for lateral density variation below the ice. Solutions with regional gravity offsets greater than or equal to10 mGal and density contrasts less than or equal to0.30 g/cm/sup 3/ are possible. We cannot unambiguously attribute the anomalous gradient to a breakdown of Newtonian gravity because there remains the possibility it is due to unexpected geological features in the rock below the ice. 11 refs., 6 figs., 1 tab.
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