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Hubble Spots Mysterious Flash of Light on Jupiter
By Robert Roy Britt
Senior Science Writer
posted: 02:00 pm ET
11 April 2001
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jupiter_flare A brief but bright flash of light as big as Earth spotted near Jupiter's north pole by the Hubble Space Telescope has scientists stumped. When the flare erupted, researchers were using Hubble to study an auroral oval, one of two permanent rings of light that glow in the atmosphere above Jupiter's poles. The flare, centered inside the northern oval, was five times brighter than the aurora and lasted about five minutes, peaking intensely during a one-minute stretch. "The flare is far brighter than anything we've seen before at Jupiter," said Randy Gladstone of the Southwest Research Institute. "The amount of energy released is comparable to an atomic bomb blast." A paper on the discovery appears in the April 12, 2001 issue of the journal Nature. Lead author J. Hunter Waite, of the University of Michigan, told SPACE.com that additional Hubble observations showed a handful of smaller flares, pointing to the possibility that such events are fairly routine. Waite said only Hubble has the sensitivity to spot the events, explaining why they had not been seen before. Similar to Earth's northern lights Jupiter is an extremely active planet. Storms in its upper atmosphere are the largest and oldest known in the solar system. And being so big, Jupiter generates a large magnetic field, whose effects are not fully understood. Jupiter's auroral oval is similar to the colorful aurorae on Earth. These terrestrial light shows grace the far northern and southern night skies when charged particles called electrons, riding away from the Sun on the solar wind, slam into our planet's protective magnetic field. The interaction triggers a release of light energy. On Jupiter, the electrons needed to produce aurora are closer at hand. Volcanoes on Io, a moon of Jupiter, hurl sulfur, oxygen and small dust particles into space. This debris is lured by gravity toward Jupiter, and it is energized as it spirals inward and travels along invisible but powerful magnetic field lines toward the planet's poles. Jupiter's rotation provides the root energy source for all this activity. Io's gas and dust expulsions are dragged around the planet's midsection in a vast sheet, much like a loose-fitting skirt on a pirouetting ballerina. With Io providing a source of electrons, particles riding on the solar wind are thought to be only a minor contributor to Jupiter's auroral oval, especially since the solar wind is significantly weakened by the time it reaches Jupiter (which is more than five times as far from the Sun as Earth). But Waite and his colleagues speculated that pulses in the solar wind, which increase its pressure, might be responsible for the sudden Jovian flares. Bursts of solar wind are known to create similar but less intense fluctuations in Earth's aurora.Like television "The process is much like a TV where accelerated electrons hit the picture tube and cause the image," Waite explains. "In this case the Earth's or Jupiter's energetic magnetospheric particles are the exciters and the atmospheric gases are the TV screen." Solar wind conditions at the time of the Jovian flare were not unusual, Waite and his colleagues write in Nature. What appear to be typical pulses of solar wind activity were recorded by other space-based equipment, though not with certainty. The authors say that this apparently normal solar activity at the time of the largest Jovian flare "suggests that such flares, if indeed triggered by changes in solar-wind pressure, may not be uncommon." Additional clues may be hidden in data that have been gathered by both the Cassini and the Galileo spacecraft, but which has not yet been analyzed, the researchers say. The Hubble observations were made in September 1999, taken in the far-ultraviolet wavelengths of the light spectrum.Click here for more news and information about the planets of our solar system.
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