Blobs of electrified particles spew violently from the Sun, zoom at "warp speed" toward Earth's magnetic field, and trigger an unusual form of aurora, scientists have discovered using an ultraviolet camera on NASA's Polar spacecraft.
These electrified blobs, called coronal mass ejections, travel at more than 1.5 million miles per hour, or 2,000 times the speed of sound, and create interplanetary shock waves that "ram into" Earth's magnetic field. This is roughly comparable to the way a supersonic aircraft breaks the sound barrier and creates a shock wave that we hear as a sonic boom. With the aurora, the effect of the interplanetary shock wave is not heard, but instead is seen as a multi-colored display by Polar.
The more common type of Earth aurora is formed through a process that begins when the magnetic fields that extend from Earth's Poles are dragged away from the Sun and Earth by the solar wind. When these magnetic fields collide, they annihilate each other and ultimately create a hot, electrified gas that produces an eerie, colorful display near midnight at high and low latitude locations such as Alaska and Antarctica. We call those displays the northern and southern lights.
These newly discovered auroras appear in those same latitude regions -- but unlike the better known auroras, they appear at high noon, when they would usually be obscured by the Sun. That would explain why no one on Earth has reported seeing them yet. In addition, these dayside auroras move much, much faster and in the opposite direction from ordinary auroras.
"This sheds new light on the way the Sun's tumultuous activities affect us here on Earth," said Dr. Bruce Tsurutani of NASA's Jet Propulsion Laboratory, co-investigator for the Polar camera. "Since this type of aurora has not been seen by earthlings, it's a prime example of a robotic spacecraft finding things we'd never know about otherwise."
"Originally NASA's Wind spacecraft was used to find interplanetary shocks," said Dr. Xiaoyan Zhou, a National Research Council resident research associate who is also on the Polar science team. "We wanted to find out what effect these shocks have on Earth. We were surprised to discover that they caused these unusual, fast-moving auroras." Polar's instruments confirmed their existence with a dozen sightings. These latest aurora findings were based on data gathered during the past two years.
Now that scientists are aware of the new form of auroras, they hope professional and amateur Earth observers will look for the phenomenon at certain locations like Spitzbergen, Norway in the winter, when the skies are dark at noon. "We're anxious to know what these new auroras look like when seen from Earth," Tsurutani said.
More will be learned about these space blobs, or coronal mass ejections, when NASA's planned Solar Probe spacecraft flies closer to the Sun's sizzling surface than any previous spacecraft. Solar Probe will launch in 2007 and will approach to a distance of only 1-1/2 times the Sun's diameter in 2010, surviving temperatures above 3,700 degrees Fahrenheit.
"I can hardly wait to see close-up pictures of a coronal mass ejection when the spacecraft flies through one as it's being formed," said Tsurutani, who also serves as Solar Probe project scientist.
The Polar and Wind missions are managed by Goddard Space Flight Center, Greenbelt, MD, for NASA's Office of Space Science, Washington, DC. The two spacecraft are part of the International Solar-Terrestrial Physics program. Solar Probe is managed by JPL as part of the Outer Planets/Solar Probe project. JPL is a division of the California Institute of Technology, Pasadena, CA.
For a picture go to http://www.jpl.nasa.gov/releases/99/aurora.pdf. (Adobe Acrobat Reader required).
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