(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-