Jupiter Lights Up     image of PDF button

Researchers observe an unusually bright flare from the planet with the most powerful auroras in the solar system.

A team of researchers from the University of Michigan at Ann Arbor, Southwest Research Institute, Science Applications International Corporation and the University of California at Los Angeles spotted a brief, bright auroral flash near Jupiter's north pole, believed to be fueled by the solar wind. An animation of the flare event can be viewed at http://pluto.space.swri.edu/yosemite/jupiter/flare.html. NASA funded the auroral observations.

During observations of Jupiter's aurora, a team of researchers that included staff from Southwest Research Institute (SwRI) discovered a rapidly evolving, extraordinarily bright flare. The observations, taken at far-ultraviolet wavelengths, were made using the Hubble Space Telescope Imaging Spectrograph. This is the first time such an intense and short-lived auroral emission has been reported.

Auroras develop on Earth when the solar wind interacts with the magnet-osphere, the magnetic field surrounding the planet and containing charged particles. The auroras on Jupiter--the most powerful in the solar system--are fed largely by energy extracted from planetary rotation. Evidence suggests the solar wind may contribute to their formation as well.

As described in a recent issue of Nature, the team observed a rapidly intensifying, flare-like auroral emission at latitudes between 60° and 70° during the second of four auroral observations recorded Sept. 21, 1999. Within seconds, the intensity of the emission increased by a factor of 30 and then decreased on a similar time scale.

The flare, which stretched several thousand kilometers across, reached a peak brightness of 37 megaRayleighs (MR). Other auroral emissions remained virtually unchanged in intensity and morphology during the flare event.

A similar event, although shorter-lived and less intense than the flare, also occurred during the first observation. It reached a maximum brightness of 17 MR. No unusual flares were seen in the third and fourth observations.

"The flare is far brighter than anything we've seen before at Jupiter," said Dr. Randy Gladstone, a staff scientist in the SwRI Space Science and Engineering Division. "The amount of energy released is comparable to an atomic bomb blast."

The team used models to locate the magnetospheric source region of the charged particles that triggered the flare, but the nature and cause of the disturbance is not known. One possible explanation involves solar wind pressure pulses hitting the jovian magnetosphere.

Propagation of solar wind data from the Solar Wind Electron Proton Alpha Monitor (SWEPAM) on the Advanced Composition Explorer (ACE) spacecraft showed a series of sharp rises in the solar wind dynamic pressure at the orbit of Jupiter near the time researchers observed the flare. Previous studies have shown a correlation between changes in solar wind pressure and changes in the intensity of auroral emissions at both infrared and radio wavelengths.

More recent data from coordinated Cassini, Hubble Space Telescope and Galileo observations taken in December 2000 provide near-simultaneous monitoring of solar wind conditions, auroral activity and magnetospheric conditions around Jupiter and are now being analyzed.

"We expect the data from these observations to give us some insight into whether or not the solar wind plays a role in transient events like the one we saw," said coauthor Dr. Bill Lewis, also of SwRI. The data could also yield dramatic new insights into jovian auroral phenomena overall and the underlying magnetospheric processes.

Comments about this article? Contact Gladstone at (210) 522-3581 or rgladstone@swri.org.

Published in the Summer 2001 issue of Technology Today®, published by Southwest Research Institute. For more information, contact Maria Stothoff.

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