176 lines
7.4 KiB
Plaintext
176 lines
7.4 KiB
Plaintext
SUBJECT: GRAVITATIONAL WAVE SEARCH FILE: UFO3003
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MUFONET-BBS GROUP - MUFONET-BBS NETWORK
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SPACE NEWS - WIRE
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3/17/93: 3 SPACECRAFT TO CONDUCT 3-WEEK
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GRAVITATIONAL WAVE SEARCH
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Donald L. Savage
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Headquarters, Washington, D.C. March 17, 1993
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Franklin O'Donnell
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Jet Propulsion Laboratory, Pasadena, Calif.
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RELEASE: 93-48
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Three interplanetary spacecraft, now headed quietly toward
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Mars, Jupiter and over the poles of the sun, soon may prove
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the existence of elusive waves in the universe's
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gravitational field by bobbing on ripples in space like
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corks bobbing on ripples in a pond.
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Such waves of gravity have never been directly detected,
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although their existence was predicted decades ago in
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Einstein's theory of relativity and there is indirect
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evidence that they exist. The waves are believed to be
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produced by supernova explosions, collapsing black holes and
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other catastrophic events. Past searches with ground-based
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equipment and single spacecraft have failed to discover
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them.
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Astrophysicists are hoping to make this major discovery by
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spending the next few weeks "listening" for passing
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gravitational waves with three "borrowed" spacecraft at the
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same time in the most sensitive detection system yet
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assembled to search for very low frequency gravitational
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waves.
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The spacecraft, now on their way to separate destinations in
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the solar system, are NASA's Mars Observer, Galileo and the
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European Space Agency (ESA) Ulysses spacecraft.
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The joint NASA-ESA experiment will run from March 21 to
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April 11, marking the first time three spacecraft will make
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observations simultaneously, greatly increasing the
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reliability of any detection.
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"If this experiment succeeds in detecting gravitational
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waves it may answer fundamental questions about the nature
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of gravity as well as give further support for Einstein's
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theory of general relativity," said Dr. Robert Stachnik,
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Gravitational Wave Program Scientist in NASA's Astrophysics
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Div., Office of Space Science, Washington, D.C.
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"We're also very excited about the possibility of making a
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major discovery with such a cost-effective experiment. We
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were able to take advantage of three spacecraft already in
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space which soon will be in the correct relative positions
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and distances we need to do this experiment. We can just
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borrow them for a few weeks, without any added cost for
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equipment and no change to their missions. It's big science
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on a small budget," Stachnik said.
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"Einstein predicted the existence of gravitational waves in
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his theory of general relativity, and radio astronomy
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observations of pulsars have suggested they indeed exist --
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but no one has ever detected a gravitational wave directly,"
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said Dr. John W. Armstrong of NASA's Jet Propulsion
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Laboratory, Pasadena, Calif., who will work with the Mars
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Observer and Galileo spacecraft.
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The experiment is built around a simple concept. During the
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3-week experiment, the antennas of NASA's Deep Space
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Network (DSN) on Earth will beam radio signals to the three
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spacecraft at precisely known frequencies. Each spacecraft
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will send signals back to Earth at the same frequency it
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receives. If no gravitational waves are passing through the
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Solar System, the signals returned to Earth should have
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exactly the same frequencies as the original signals sent
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from the DSN, shifted only by the Doppler effect of
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spacecraft motion.
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However, if a strong enough gravitational wave passes --
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produced perhaps from collapsing masses of stars in the
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hearts of galaxies or from the spiraling together and
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collision of two black holes -- both the Earth and the
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spacecraft will experience a slight "bobbing" from the
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ripple-like passage of the gravitational wave. This
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interaction cannot be directly detected at either the Earth
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or the spacecraft alone, but would show up as a slight
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change in the frequency of the radio signal finally received
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back at Earth.
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The hydrogen maser clocks that control the DSN transmitters
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and receivers are so accurate that scientists will be able
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to detect a change in radio frequency of as little as a few
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parts in a quadrillion (a quadrillion is 1 followed by 15
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zeroes).
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"This should allow us to detect gravitational waves from
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objects such as massive pairs of black holes hidden in the
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hearts of other galaxies," said Hugo D. Wahlquist of JPL,
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who will work on the Ulysses spacecraft with Sami W. Asmar
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of JPL, Prof. Bruno Bertotti of the University of Pavia,
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Italy, and Prof. Luciano Iess of the University of Rome La
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Sapienza.
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Scientists emphasize, however, that snaring a gravitational
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wave during the 3-week experiment will depend on a good bit
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of luck -- whether a suitable astronomical event happens to
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occur during the relatively brief opportunity when data can
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be taken. All three spacecraft will be in the Earth's night
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sky at that time, so interference with their radio signals
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due to charged particles in the solar wind will be at a
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minimum.
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Successful detection of gravitational waves could open up an
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entirely new kind of astronomy. Because the gravitational
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waves do not readily interact with matter, detecting them
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may open a window to the interiors of powerful -- and
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sometimes catastrophic -- events such as supernova
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explosions and collapsing black holes.
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"Gravitational wave research is now in the hands of
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physicists. Once signals are detected, the astronomers will
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be beating down the doors," said Stachnik.
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Sensitive ground-based interferometer antennas now are being
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built in both the United States and Europe to search for
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gravitational waves with wavelengths of thousands of
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kilometers.
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"In addition to searching for the shorter waves that can
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affect antennas here on Earth, we now will be using radio
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signals sent to spacecraft hundreds of millions of
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kilometers away to search for waves of much longer
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wavelength," said Dr. Frank B. Estabrook of JPL, who will
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work with the Galileo spacecraft.
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Detection of the gravitational waves, even if they occur,
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will still take at least several months of patient data
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analysis. "The spacecraft systems can detect large enough
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gravitational waves, if they exist," said Dr. Bevan M.
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French, Program Scientist for the Mars Observer. "But it
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won't be one of those sudden 'Eureka!' situations. We'll be
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looking for a few small wiggles in a huge amount of radio
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data. It will take time."
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To identify the unique signals of gravitational waves, the
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scientists also will have to eliminate such mundane effects
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as planned changes in the orientation of the spacecraft,
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interference from charged particles (plasmas) in space and
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even atmospheric changes, rain and snow on Earth.
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Mars Observer, launched in September 1992, will reach the
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Red Planet Aug. 24 of this year. Launched in 1989, NASA's
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Galileo spacecraft will arrive at Jupiter in 1995. The ESA
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Ulysses spacecraft was launched in 1990, and it will fly
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over the sun's poles in 1994 and 1995.
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Gravitational wave research is supported by the Astrophysics
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Division of NASA's Office of Space Science and by each of
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the three spacecraft projects, which scheduled the radio
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searches during their interplanetary cruise periods.
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-END OF FILE-
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**********************************************
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* THE U.F.O. BBS - http://www.ufobbs.com/ufo *
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