"For the first time ever we can produce high resolution images or "snapshots" of our atmosphere. We can view them singly or combine them to make movies which allows us to track magnetic storms in the space just outside the Earth1s atmosphere," says Dr. Harlan E. Spence, assistant professor of astronomy at Boston University and lead investigator on the project. "From these images we can begin to answer fundamental questions about the relationship between Earth and the Sun, and how our near-Earth space environment responds to eruptions on the Sun to produce space weather."
Results of the initial POLAR ENA analyses are being presented by Professor Spence and his collaborators, Dr. Geoffrey Reeves from Los Alamos National Laboratory and Dr. Blake at the International Solar-Terrestrial Physics conference at the American Geophysical Union meeting in San Francisco, Calif. this week.
Space weather is created when the energetic charged particles and magnetic fields of the Sun blow past and meet the magnetic field of the earth. The interaction of these energy fields can produce magnetic storms in space which in turn create dazzling effects in the atmosphere such as the aurora borealis, or "northern lights." It can also affect or damage satellites used for communication, navigation and weather prediction.
Dr. Theodore A. Fritz, professor of astronomy at Boston University and co-principal investigator, explains, "We have learned much over the last three decades about the particles populating space near Earth and how they change during magnetic storms. Until now, however, we have been severely limited in our ability to simultaneously sample large regions of space to get the Obig picture.1 The new images are unprecedented in their capacity to provide that fresh perspective needed to really push the frontiers of new knowledge." The NASA POLAR spacecraft was launched into Earth orbit in late February 1996 carrying an Imaging Proton Spectrometer (IPS) developed by Dr. J. Bernard Blake of The Aerospace Corporation, El Segundo, Calif., principal investigator on the project.
The IPS records energetic neutral atoms (ENAs) to produce the images. ENAs are created when the cold neutral gases of the atmosphere interact with the very energetic charged particles trapped in the Van Allen radiation belts which encircle the Earth1s equatorial region at high altitudes (~10,000 km). They are detected by the IPS from even higher altitudes (~50,000 km) over the earth1s northern geographic pole. Large numbers of ENAs are produced during periods of increased Van Allen belt intensity, called magnetic storms, which are associated with solar eruptions, called coronal mass ejections. Although no large magnetic storms have occurred thus far during the POLAR mission, several smaller storms have already produced significant ENA events which lead investigators to believe that even better images will be obtained.
"The POLAR mission is part of a larger international program to study the complex connections between the Sun as a star and the Earth as a planet," says Dr. Robert Hoffman, the POLAR Project Scientist at the NASA Goddard Space Flight Center which supports the mission. "The ENA images from POLAR are an exciting new way of visualizing an important aspect of this crucial interaction."
"The preliminary ENA movies are already generating a great deal of excitement within the scientific community. Especially exciting is our new ability to view the regions of space thought to produce the aurora," notes Spence. "A team was recently selected to design the next-generation satellite for a NASA mission called IMAGE specifically for ENA imaging. IMAGE will build on our experience."
Dr. Mark Smith, the IMAGE Mission Scientist at the NASA/GSFC, sums it up by saying, "Imaging the near-Earth space environment is a top priority within NASA and the POLAR data are already providing new and unanticipated insights. We intend to use the experience gained with POLAR to learn how to optimize the IMAGE mission design."
Scientists at the Center for Space Physics use satellites, rockets and ground-based instruments to study the upper atmospheres and plasma environments of the Earth, the planets, moons, comets, interplanetary space and the Sun. The Center is an interdisciplinary research facility at Boston University that links programs in the Colleges of Arts and Science and of Engineering. In addition to the NASA POLAR mission, upcoming missions include TERRIERS, Boston University1s own satellite that is being readied for launch in summer 1997; the Cassini mission to Saturn; and Rosetts/Champollion, a small sub-satellite that will land on a comet in the next century.
POLAR movies and images may be found at the POLAR web site