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As the world turns, it drags space and time



 
 
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Old October 21st 04, 11:15 PM
Jacques van Oene
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Default As the world turns, it drags space and time


Donald Savage
Headquarters, Washington Oct. 21, 2004
(Phone: 202/358-1547)

Krishna Ramanujan
Goddard Space Flight Center, Greenbelt, Md.
(Phone: 607/273-2561)

RELEASE: 04-351

AS THE WORLD TURNS, IT DRAGS SPACE AND TIME

An international team of NASA and university researchers
has found the first direct evidence the Earth is dragging
space and time around itself as it rotates.

The researchers believe they have measured the effect, first
predicted in 1918 by using Einstein's theory of general
relativity, by precisely observing shifts in the orbits of
two Earth-orbiting laser-ranging satellites. The researchers
observed the orbits of the Laser Geodynamics Satellite I
(LAGEOS I), a NASA spacecraft, and LAGEOS II, a joint
NASA/Italian Space Agency (ASI) spacecraft.

The research, reported in the journal Nature, is the first
accurate measurement of a bizarre effect that predicts a
rotating mass will drag space around it. The Lense-Thirring
Effect is also known as frame dragging.

The team was led by Dr. Ignazio Ciufolini of the University
of Lecce, Italy, and Dr. Erricos C. 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 Baltimore County.

"General relativity predicts massive rotating objects should
drag space-time around themselves as they rotate," Pavlis
said. "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 Earth."
The study is a follow-up to earlier work in 1998 where the
authors' team reported the first direct detection of the
effect.

The previous measurement was much less accurate than the
current work, due to inaccuracies in the gravitational model
available at the time. Data from NASA's GRACE mission allowed
for a vast improvement in the accuracy of new models, which
made this new result possible.

"We found 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. "Our measurement
agrees 99 percent with what is predicted by general
relativity, which is within our margin of error of plus or
minus five percent. Even if the gravitational model errors
are off by two or three times the officially quoted values,
our measurement is still accurate to 10 percent or better."
Future measurements by Gravity Probe B, a NASA spacecraft
launched in 2004, should reduce this error margin to less
than one percent. This promises to tell researchers much more
about the physics involved.

Ciufolini's team, using the LAGEOS satellites, previously
observed the Lense-Thirring effect. It 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, precise
measurement of this phenomenon at the five to 10 percent
level. The team analyzed an 11-year period of laser ranging
data from the LAGEOS satellites from 1993 to 2003, using a
method devised by Ciufolini a decade ago.

The measurements required the use of an extremely accurate
model of the Earth's gravitational field, called EIGEN-
GRACE02S, which became available only recently, based on an
analysis of GRACE data. The model was developed at the
GeoForschungs Zentrum Potsdam, Germany, by a group who are
co-principal investigators of the GRACE mission along with
the Center for Space Research of the University of Texas at
Austin.

LAGEOS II, launched in 1992, and its predecessor, LAGEOS I,
launched in 1976, are passive satellites dedicated
exclusively to laser ranging. The process entails sending
laser pulses to the satellite from ranging stations on Earth
and then recording the round-trip travel time. Given the
known value for the speed of light, this measurement enables
scientists to precisely determine the distances between laser
ranging stations on Earth and the satellite.
NASA and Stanford University, Palo Alto, Calif. developed
Gravity Probe B. It will precisely check tiny changes in the
direction of spin of four gyroscopes contained in an Earth
satellite orbiting 400-miles directly over the poles. The
experiment will test two theories relating to Einstein's
Theory of General Relativity, including the Lense-Thirring
Effect. These effects, though small for Earth, have far-
reaching implications for the nature of matter and the
structure of the universe. For graphics and other material
about this research on the Web, visit:
http://www.nasa.gov/vision/earth/loo.../earth_drag.ht
ml

-end-

--
---------------------------

Jacques :-)

www.spacepatches.info



 




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