The Earth's gravity is generally perceived as a constant, with one "g" indicating an acceleration of 9.8 meters per second per second. However, small variations in the gravitational field are discernable at different locations, typically with magnitudes of one-ten thousandth of the average gravitational attraction, implying a "mass deficit" in such places. These undulations, known as gravity anomalies, are spread throughout the Earth, but one of the largest is centered over Hudson Bay, Canada. Using a new approach to analyzing planetary gravity fields, two geophysicists, Mark Simons at the California Institute of Technology and Bradford Hager at M.I.T., have shown that incomplete glacial rebound can account for a substantial portion of the Hudson Bay gravity anomaly. About 18,000 years ago, Hudson Bay was at the center of a continental-sized glacier with a thickness of several kilometers. The weight of the ice bowed the surface of the Earth down and after it receded, it left depression in its wake. Having an estimate of incomplete post-glacial rebound allowed Simons and Hager to derive a model of how the viscosity of the mantle changes with depth. Their favored model suggests that underneath the oldest parts of continents the viscosity of the outer 400 kilometers of Earth is much stiffer than under the oceans. Therefore, these continental keels can resist the erosion by the convective flow that drives plate tectonics. For more information, Robert Tindol, "Caltech", at (626) 395-3631.
Two researchers from Cornell University have won a $100,000 grant from NASA to continue work to develop an energy-harvesting robotic eel the space agency aims to use to explore oceans on one of the moons of Jupiter.
Is the factory smarter than it used to be? From recent buzzwords, you’d think we’ve entered a new dimension in industrial plants, where robots run all physical functions wirelessly and humans do little more than program ever more capable robotics. Some of that is actually true, but it’s been true for a while.
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