New Way to the Center of the Earth

New Way to the Center of the Earth

Humans have yet to see Earth's center, as did the characters in Jules Verne's science fiction classic, "Journey to the Center of the Earth." But a new NASA study proposes a novel technique to pinpoint more precisely the location of Earth's center of mass and how it moves through space.

Knowing the location of the center of mass, determined using measurements from sites on Earth's surface, is important because it provides the reference frame through which 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.

The accuracy of estimates of the motion of Earth's center of mass is uncertain, but likely ranges from 2 to 5 millimeters (.08 to .20 inches) a year. 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. The four techniques were developed and/or operated by NASA in partnership with other national and international agencies. Results of the new study appear in the June issue of Geophysical Journal International.

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.

"The past two international estimates of the motion of the Earth system's mass center, made in 2000 and 2005, differ by 1.8 millimeters (.07 inches) a year," he said. "This discrepancy suggests the motion of Earth's mass center is not as well known as we'd like."

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.

Study of underground lakes in Antarctica could be critical, prof says

Study of underground lakes in Antarctica could be critical, prof says

Study of underground lakes in Antarctica could be critical, prof says

The discovery of interconnected lakes beneath kilometers of ice in Antarctica could be one of the most important scientific finds in recent years, but proper procedures need to be established before investigation begins, says a Texas A&M University scientist who is a leader in the research efforts. 

 

Mahlon "Chuck" Kennicutt II, professor of oceanography and director of the Sustainable Development Program in Texas A&M's Office of the Vice President for Research, says the National Science Foundation and 11 countries involved in the research and exploration are seeking agreement on how best to study these unique environments, which include at least 145 lakes under Antarctica's massive ice sheets. Several of the lakes are immense, and one, Lake Vostok, is similar in size to Lake Ontario, roughly 5,400 square miles, scientists note.

Participants in the project known as The Russian Antarctic Expedition have announced their intentions to penetrate Lake Vostok during the coming Antarctic field season.

"These lakes were rediscovered within the past 10 years or so, but no one yet has penetrated them and we want to make sure that the research is done properly and adheres to the highest environmental stewardship principles," says Kennicutt, who also serves as a director of the SALE (Subglacial Antarctic Lake Environments) office, which is maintained at Texas A&M.

"This has the potential to be one of the most important scientific discoveries in years, since sub-ice water appears to be an important player in many different processes fundamental to Antarctica and our planet.

"We believe that these lakes are part of an interconnected system that spans the entire Antarctic continent," he adds. "These bodies of water are several miles beneath the ice sheet which took millions of years to form, meaning these lakes have been undisturbed and disconnected from our atmosphere for hundreds of thousands of years. It is highly likely that unique microbial communities that we never knew existed are lake residents."

A group of scientists, including Kennicutt, who also serves as an adviser to the National Science Foundation, the agency that funds and oversees all U.S. science in Antarctica, will meet in Big Sky, Mont., this week to discuss research procedures for studying sub-ice environments. The meeting closely follows the release of a report by the National Academies on environmental issues related to sub-ice exploration that provides guidance for future lake penetration.

Scientists from the countries involved, which include the U.S., France, Italy, Japan, Russia, the United Kingdom and others, have concluded that lake entry and sampling will ultimately be necessary to accomplish the ambitious research objectives, Kennicutt notes.

"How to do this in the best way to preserve these environments and to be least invasive is a key question that needs further discussion," he notes.

"The countries involved have all agreed we must do as much as possible to avoid altering the lakes or causing any environmental damage."

Research in Antarctica has always had a special set of rules among nations.

It is the only continent on Earth that is managed through an international treaty signed by 45 countries representing two-thirds of the world's population. By unanimous consent of these nations, Antarctica has been viewed as a continent for science, research and peace.

The Department of State coordinates U.S. policy on Antarctica and works closely with the National Science Foundation, which administers and manages the U.S. Antarctic Program. Kennicutt also assists the NSF's Office of Polar Program.

"We are probably 3-5 years away from conducting U.S. research on these underground lakes," Kennicutt believes.

"We believe these lakes may exert important controls on large ice sheet movement and that they are just like above-groundwater systems and include a range of features such as streams, rivers and lakes, only they are under kilometers of ice. Once the U.S. becomes fully engaged in these research efforts, this will almost certainly be one of the dominant Antarctic research focus areas for at least the next decade, if not longer."