NASA's 'Journey' to the Center of Earth
Knowing the location of the Earth's center of mass provides the frame through which NASA's scientists determine the relative motions of positions on Earth's surface, in its atmosphere, and in space.
This information is vital to the study of global sea-level change, earthquakes, volcanoes, and Earth's response to the retreat of ice sheets after the last ice age.
In 1864 Jules Verne published his classic Journey to the Center of the Earth. The novel tells the story of a professor who leads his nephew and hired guide down a volcano in Iceland to the "center of the Earth". En route they encounter prehistoric animals and natural hazards, eventually coming to the surface again.
Verne's fiction underscores the vast strides in our knowledge of our planet's interior. We now know that all continents are masses of low-density rock embeded in a ground mass of more dense material that cloaks a molten hot radioactive interior that creates gigantic convection cells of hot liquid rock in the mantle. These massive convection cells carry the thin, brittle outer layer the tectonic plates along with them creating our continents or smaller land masses caught in the moving outer skin.
Beneath Earth's mantle are two cores: a solid inner cpore and a liquid outer one. The pressure at the center of the Earth are estimated to be over three million times greater than at the surface turing any rock there solid. Temperature at the core is between 7,000 degrees F to 13,000 degrees F -as hot as the surface as the Sun, revolving like an electrical motor creating the magnetic field, which reverses itself every 500,000 years or so.
Since Verne's 19th-century classic, the study of paleomagnetics have allowed for the reconstruction of ancient continental positions; oceanographic research has revealed the presence of enormous underwater volcanic centers where the sea floor literally pulls away from itself.
A new NASA study proposes a novel technique to pinpoint more precisely the location of Earth's center of mass and how the planet moves through space.
Donald Argus of NASA's Jet Propulsion Laboratory, Pasadena, Calif., developed the new technique, which estimates Earth's center of mass to within 1 millimeter (.04 inches) a year by precisely positioning sites on Earth's surface using a combination of four space-based techniques.
Scientists currently define Earth's center in two ways: as the mass center of solid Earth or as the mass center of Earth's entire system, which combines solid Earth, ice sheets, oceans and atmosphere. Argus says there is room for improvement in these estimates.
Argus argues that movements in the mass of Earth's atmosphere and oceans are seasonal and do not accumulate enough to change Earth's mass center. He therefore believes the mass center of solid Earth provides a more accurate reference frame.
"By its very nature, Earth's reference frame is moderately uncertain no matter how it is defined," Argus said. "The problem is very much akin to measuring the center of mass of a glob of Jell-O, because Earth is constantly changing shape due to tectonic and climatic forces. This new reference frame takes us a step closer to pinpointing Earth's exact center."
Argus says this new reference frame could make important contributions to understanding global climate change. The inference that Earth is warming comes partly from observations of global sea level rise, believed to be due to ice sheets melting in Greenland, Antarctica and elsewhere. In recent years, global sea level has been rising faster, with the current rate at about 3 millimeters (.12 inches) a year. Uncertainties in the accuracy of the motion of Earth's center of mass result in significant uncertainties in measuring this rate of change.
"Knowing the relative motions of the mass center of Earth's system and the mass center of the solid Earth can help scientists better determine the rate at which ice in Greenland and Antarctica is melting into the ocean," Argus explained. He said the new frame of reference will improve estimates of sea level rise from satellite altimeters like the NASA/French Space Agency Jason satellite, which rely on measurements of the location and motion of the mass center of Earth's system.
"For scientists studying post-glacial rebound, this new reference frame helps them better understand how viscous [gooey or sticky] Earth's solid mantle is, which affects how fast Earth's crust rises in response to the retreat of the massive ice sheets that covered areas such as Canada 20,000 years ago," he said. "As a result, they'll be able to make more accurate estimates of these vertical motions and can improve model predictions."
Scientists can also use the new information to more accurately determine plate motions along fault zones, improving our understanding of earthquake and volcanic processes.
The new technique combines data from a high-precision network of global positioning system receivers; a network of laser stations that track high-orbiting geodetic satellites called Laser Geodynamics Satellites, or Lageos; a network of radio telescopes that measure the position of Earth with respect to quasars at the edge of the universe, known as very long baseline interferometry; and a French network of precise satellite tracking instruments called Doppler Orbit and Radiopositioning Integrated by Satellite, or DORIS.
Posted by Casey Kazan.
I think this new method of studying the earth can be used to study other planets, or at least those in our solar system that fit the bill. http://thenewsroom.com/details/400003/Health?c_id=wom-bc-ar
- Alvin from The Sci-Tech Desk at TheNewsRoom.com
Posted by: alvinwriter | June 13, 2007 at 08:08 PM