First Images Of Earth's Plasma Sheet

TERRADAILY

"When the plasma sheet is empty and the IMF is southward, nothing much happens. When the plasma sheet is full and the IMF is northward, again, nothing happens," McComas says. "But when the plasma sheet is full and the IMF turns southward, the plasma sheet pumps out its contents, and that's when things really start to get interesting around Earth."

San Antonio - Dec 12, 2002
Observations led by Southwest Research Institute (SwRI) using NASA's Imager for Magnetopause-to-Aurora Global Exploration (IMAGE) spacecraft may lead to a new, critical technique for monitoring and predicting space weather.

The team, including researchers from Los Alamos National Laboratory, used the medium-energy neutral atom (MENA) instrument aboard the IMAGE satellite to watch the first global images of the plasma sheet, a slab of plasma that reaches tailward through the Earth's magnetic field, or magnetosphere.

The observations revealed that the solar wind fills the sheet with high-density plasma that is later squeezed toward the Earth when the interplanetary magnetic field orientation points southward.

These conditions correlate with the occurrence of geomagnetic storms that create aurorae and have the potential to disrupt ground-based electronic communications and harm orbiting satellites.

"Space scientists had pieced together this concept based on single-point measurements, but this is the first study that really lets us observe the plasma sheet filling and emptying into the inner magnetosphere in response to solar wind conditions," says Dr. David J. McComas, executive director of the SwRI Space Science and Engineering Division.

During a 20-day period, the team observed several geomagnetic storms.

Results indicate that the two most important factors to observe in order to monitor and predict such storms are the orientation of the interplanetary magnetic field (IMF) and the amount of material in the plasma sheet.

The space science community understood that a significant southward interplanetary magnetic field is required to empty the plasma sheet to create these storms. However, there had not been a way to measure the fullness of the plasma sheet reservoir -- until now.

SwRI managed the development of the IMAGE spacecraft and built the MENA instrument in cooperation with Los Alamos. Since its launch in February 2000, the spacecraft has yielded the first global images of the Earth's magnetosphere, the region of space controlled by the Earth's magnetic field.

Until IMAGE literally showed researchers the magnetospheric processes that occur around Earth, scientists using single-point measurements from charged particle detectors, magnetometers, and electric field instruments found it difficult to piece together a bigger picture of the magnetospheric forces in action.

The Two Wide-angle Imaging Neutral-atom Spectrometers (TWINS) mission, slated for launches in late 2003 and 2005, will significantly extend researchers' ability to image the near space environment by providing stereoscopic viewing of the magnetosphere for the first time.

IMAGE, a Medium-class Explorer mission, is managed by NASA Goddard Space Flight Center in Greenbelt, Md. for the Office of Space Science in Washington. SwRI has overall responsibility for IMAGE science, instrumentation, spacecraft, and data analyses.

The paper, "Filling and Emptying of the Plasma Sheet: Remote Observations with 1-70 keV Energetic Neutral Atoms," by D.J. McComas (SwRI), P. Valek (SwRI), J.L. Burch (SwRI), C.J. Pollock (SwRI), R.M. Skoug (Los Alamos), and M. F. Thomsen (Los Alamos) appears in the Dec. 4, 2002, issue of Geophysical Research Letters.

EARLY EARTH

Two-Billion-Year-Old Surprise Found Beneath The Azores

Bristol - Nov 26, 2002
Geologists may have to revise their ideas about what goes on in the Earth's interior, following the publication today of new research in the journal Nature.

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