(fwd) Earth Dragging Space and Time as It Rotates
Sue J. Worden (worden@uts.cc.utexas.edu)
Mon, 30 Mar 1998 07:52:28 -0600 (CST)
> Date: Fri, 27 Mar 1998 17:30:35 -0500 (EST)
> From: NASANews@hq.nasa.gov
> Subject: Earth Dragging Space and Time as It Rotates
> Douglas Isbell
> Headquarters, Washington, DC. March 27, 1998
> (Phone: 202/358-1753)
> Lynn Chandler
> Goddard Space Flight Center, Greenbelt, MD
> (Phone: 301/286-9016)
> RELEASE: 98-51
> EARTH DRAGGING SPACE AND TIME AS IT ROTATES
> An international team of NASA and university researchers has
> found the first direct evidence of a phenomenon predicted 80 years
> ago using Einstein's theory of general relativity -- that the
> Earth is dragging space and time around itself as it rotates.
> Researchers believe they have detected the effect by
> precisely measuring shifts in the orbits of two Earth-orbiting
> laser-ranging satellites, the Laser Geodynamics Satellite I
> (LAGEOS I), a NASA spacecraft, and LAGEOS II, a joint NASA/Italian
> Space Agency (ASI) spacecraft. The research, which is reported in
> the current edition of the journal Science, is the first direct
> measurement of a bizarre effect called "frame dragging."
> The team was led by Dr. Ignazio Ciufolini of the National
> Research Council of Italy and the Aerospace Department of the
> University of Rome, and Dr. Erricos Pavlis of the Joint Center for
> Earth System Technology, a research collaboration between NASA's
> Goddard Space Flight Center, Greenbelt, MD, and the University of
> Maryland at Baltimore County.
> "General relativity predicts that massive rotating objects
> should drag space-time around themselves as they rotate," said
> Pavlis. "Frame dragging is like what happens if a bowling ball
> spins in a thick fluid such as molasses. As the ball spins, it
> pulls the molasses around itself. Anything stuck in the molasses
> will also move around the ball. Similarly, as the Earth rotates,
> it pulls space-time in its vicinity around itself. This will
> shift the orbits of satellites near the Earth.
> "We found that the plane of the orbits of LAGEOS I and II
> were shifted about six feet (two meters) per year in the direction
> of the Earth's rotation," Pavlis said. "This is about 10 percent
> greater than what is predicted by general relativity, which is
> within our margin of error of plus or minus 20 percent. Later
> measurements by Gravity Probe B, a NASA spacecraft scheduled to be
> launched in 2000, should reduce this error margin to less than one
> percent. This promises to tell us much more about the physics
> involved."
> Einstein's theory of general relativity has been highly
> successful at explaining how matter and light behave in strong
> gravitational fields, and has been successfully tested using a
> wide variety of astrophysical observations. The frame-dragging
> effect was first derived using general relativity by Austrian
> physicists Joseph Lense and Hans Thirring in 1918. Known as the
> Lense-Thirring effect, it was previously observed by the team of
> Ciufolini using the LAGEOS satellites and has recently been
> observed around distant celestial objects with intense
> gravitational fields, such as black holes and neutron stars. The
> new research around Earth is the first direct detection and
> measurement of this phenomenon.
> The team analyzed a four-year period of data from the LAGEOS
> satellites from 1993 to 1996, using a method devised by Ciufolini
> three years ago. The other team members are Dr. Federico Chieppa
> of Scuola d'Ingegneria Aerospaziale of the University of Rome, and
> Drs. Eduardo Fernandes and Juan Perez-Mercader of Laboratorio de
> Astrofisica Espacial y Fisica Fundamental (LAEFF) in Madrid.
> The measurements required the use of an extremely accurate
> model of the Earth's gravitational field, called the Earth Gravity
> Model 96, which became available only recently due to the
> collaborative work of the Laboratory for Terrestrial Physics at
> Goddard, the National Imagery and Mapping Agency (formerly the
> Defense Mapping Agency), Fairfax, VA, and the Ohio State
> University, Columbus, OH. It was developed over a four-year period
> using tracking data from approximately 40 spacecraft.
> Dr. John Ries, an expert in satellite geodesy at the
> University of Texas at Austin, cautions that it is very
> challenging to remove the much larger effects of tidal changes and
> small zonal influences in the Earth's gravitational field, so that
> estimating the possible errors in the measurement of the Lense-
> Thirring effect is itself uncertain.
> "The relativistic effect being sought is about ten million
> times smaller than classical Newtonian disturbances on the plane
> of the LAGEOS orbits, requiring an enormously accurate treatment
> of background effects," said Dr. Alan Bunner, science program
> director for the Structure and Evolution of the Universe in the
> Office of Space Science at NASA headquarters, Washington, DC.
> LAGEOS II, launched in 1992, and its predecessor, LAGEOS I,
> launched in 1976, are passive satellites dedicated exclusively to
> laser ranging, which involves sending laser pulses to the
> satellite from ranging stations on Earth and then recording the
> round-trip travel time. Given the well-known value for the speed
> of light, this measurement enables scientists to determine
> precisely the distances between laser ranging stations on Earth
> and the satellite.
> LAGEOS is designed primarily to provide a reference point for
> experiments that monitor the motion of the Earth's crust, measure
> and understand the "wobble" in the Earth's axis of rotation, and
> collect information on the Earth's size, shape, and gravitational
> field. Such research is part of NASA's Earth Science enterprise,
> a coordinated research program that studies the Earth's land,
> oceans, ice, atmosphere and life as a total system.
> -end-