Researchers observe unusually bright flare from jovian aurora

San Antonio -- April 11, 2001 -- During observations of Jupiter's aurora, a team of researchers, including the University of Michigan and 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 magnetosphere, 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 the April 12 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," says 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.

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," says Gladstone. The data could also yield dramatic new insights into jovian auroral phenomena overall and the underlying magnetospheric processes.

NASA provided the funding for this program. Other team members include Dr. John T. Clarke, Dr. J. Hunter Waite, Dr. David T. Young (University of Michigan at Ann Arbor), Dr. William S. Lewis, Dr. Ray Goldstein, Dr. David J. McComas, Phil Robertson (Southwest Research Institute), Dr. Peter Riley (Science Applications International Corporation), Dr. Ray J. Walker (University of California at Los Angeles), and Shardul Desai (Washington University).

For more information contact Maria Martinez, Communications Department, Southwest Research Institute, P.O. Drawer 28510, San Antonio, Texas 78228-0510, Phone (210) 522-3305, Fax (210) 522-3547. 

An animated version of the jovian observations can be viewed at http://pluto.space.swri.edu/yosemite/jupiter/flare.html.

SwRI News SwRI Home