PHOTO RELEASE: 96-36

FIRST GLOBAL X-RAY IMAGE--This is the first global X-ray image ever obtained of the Earth's aurora. It shows a hot spot of X-rays emanating from the atmosphere near midnight at the onset of a small magnetic disturbance and a wide band of weak X-ray emissions extending through the night and morning hours to noon. It was taken on March 20, 1996 by the Polar Ionospheric X-ray Imaging Experiment (PIXIE) aboard the NASA Polar spacecraft. The image is presented in false color with the color corresponding to the measured X-ray intensity from blue (weakest) through red (strongest). The X-ray energy range covered by this image is from about 2,000 electron volts to over 10,000 electron volts. These X-rays were emitted when energetic electrons from the Earth's magnetosphere struck the upper atmosphere. The intensity of the X-rays is directly related to the intensity of the precipitated electron flux. The asymmetry in the X-ray emissions between the local time regions corresponding to early morning (over Siberia and Alaska) and late afternoon (over northern Canada and Greenland) is the result of the natural motion of energetic electrons in the Earth's magnetic field. The field causes electrons to drift to the east from their source region, probably far from Earth and near the equator on the night side at the longitude near where the X-ray intensity is highest. As they drift around the Earth, some of the electrons are lost into the atmosphere, producing the wide blue band of X-ray emissions. When the electrons reach the day side near noon, they can be swept out of the magnetosphere by the effects of large-scale electric fields. The image illustrates one of the advantages of X-ray imaging of the aurora: insensitivity to sunlight scattered off the atmosphere. The day/night terminator is indicated by the dashed line which crosses eastern Greenland, almost through the north pole, and over western Siberia. At this time North America was in daylight, Europe and Asia were in darkness. The PIXIE instrument was built at the Lockheed Martin Advanced Technology Center, with Dr. David Chenette the principal investigator.