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June 30, 1995
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Recent high-pressure, high-temperature experiments on minerals of the
Earth's lower mantle have yielded new information on the crystallography
of the region that composes the largest fraction of our planet. The experiments--by
investigators Charles Meade, Ho-kwang Mao and Jingzhu Hu of the Carnegie
Institution of Washington were conducted at the National Science Foundation's
Center for High-Pressure Research, funded by the division of earth sciences
at NSF. In recent years, scientists have studied Earth's interior by comparing
seismological data to the results of high pressure experiments. From this
work, it had been proposed that orthorhombic-structured perovskite is
the predominant phase of the lower mantle and is, therefore, the most
abundant mineral in the Earth. This hypothesis has wide ranging implications
for all earth sciences, yet has been untested to date because of inadequate
experimental capabilities for characterizing materials under the conditions
of simultaneous high pressure and temperature that exist in Earth's lower
mantle. The recent results of Meade, Mao and Hu show that the crystallography
of the lower mantle may differ significantly from previously proposed
models. These are the first experiments to have measured diffraction from
minerals at pressure and temperature conditions corresponding to depths
as great as 1650 kilometers within the Earth. The potential ramifications
for interpreting the nature and behavior of the inner planet -- the circulation
patterns of mantle convection and the driving forces of plate tectonics
-- are widespread and fundamental, according to the researchers. [Cheryl
Dybas]
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COMET SHOEMAKER-LEVY CAUSED OUTBURST IN JUPITER'S MICROWAVE RADIATION
During last July's impacts of Comet Shoemaker-Levy 9 with Jupiter, microwave
emissions from electrons in the planet's magnetic field -- as measured
by a global network of 11 Earth-based radio telescopes -- showed a dramatic
outburst, according to an article in the June 30 issue of Science. The
outburst may have been caused by a redistribution of the emitting particles,
and sheds light on the configuration of Jupiter's magnetic field. Images
from two radio telescopes -- the National Science Foundation-supported
Very Large Array and the Australia Telescope -- showed that emissions
were enhanced locally near the planet's magnetic equator. The radio telescope
network was used to monitor Jupiter's microwave emission during the impacts
and to search for changes in radiation from the planet's inner magnetosphere,
the region around Jupiter where charged particles are trapped by the planetary
magnetic field. Before the impacts, researchers had predicted the opposite:
the comet's dust would lead to a reduction in the planet's radio emissions. "The
highlight of the radio observations instead was a dramatic increase in
the radio flux density during the six days of cometary bombardment," write
the authors, 27 collaborators headed by Imke de Pater, University of California-Berkeley. "The
comet impact has provided us with a unique experiment to unravel one of
the outstanding issues in magnetospheric physics: the energization and
radial transport mechanism of the energetic electrons in Jupiter's radiation
belts," they write. [Lynn Simarski]
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NSF Director Neal Lane, in a June 26 speech to AAAS affiliates, echoed
Vannevar Bush by reminding attendees that, "Science can be effective in
the national welfare only as a member of a team." Lane said the strength
of this nation's R&D comes from a "complex interconnection of all
components" including mission agencies, research universities, national
labs, technology centers, private research foundations, various industry
consortia, small businesses, and the science and engineering workforce.
Lane stressed that a united scientific enterprise must, in a non-arrogant
manner, convey to various audiences including the public and elected representatives
-- the value and effectiveness of science and technology in society. He
also told attendees that no matter how well they perform these two tasks,
federal funding for R&D will not be exempt from cuts because of the
extraordinary tight budget times. But he urged that the scientific community
can either participate and help guide R&D funding with reasoned advice,
or not participate and let less knowledgeable people make critical decisions. [Beth
Gaston]
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