Like Earth, Saturn features active and radiant auroras at its poles. To date, our impressions of these fantastic features have been fleeting and sporadic at best. But now, using several pairs of telescopic eyes, NASA has caught its best glimpse yet of these massive, swirling auroras.
Saturn's polar auroras become active when energetic electrons fall into the planet's atmosphere and collide with hydrogen molecules. Every once in a while, a blast of fast solar wind, comprised mainly of electrons and protons, generates glowing aurora.
To capture the northern auroras in ultraviolet wavelengths, NASA used the Hubble Space Telescope (which orbits around Earth). Its Cassini spacecraft (which is around Saturn), snapped close-up views in infrared, visible-light, and ultraviolet wavelengths. Cassini could also see northern and southern parts of Saturn that don't face Earth.
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"Saturn's auroras can be fickle — you may see fireworks, you may see nothing," said Jonathan Nichols of the University of Leicester in England, who led the work on the Hubble images. "In 2013, we were treated to a veritable smorgasbord of dancing auroras, from steadily shining rings to super-fast bursts of light shooting across the pole."
The Hubble and Cassini images were focused on April and May of 2013. Images from Cassini's ultraviolet imaging spectrometer (UVIS), obtained from an unusually close range of about six Saturn radii, provided a look at the changing patterns of faint emissions on scales of a few hundred miles (kilometers) and tied the changes in the auroras to the fluctuating wind of charged particles blowing off the sun and flowing past Saturn.
"This is our best look yet at the rapidly changing patterns of auroral emission," said Wayne Pryor, a Cassini co-investigator at Central Arizona College in Coolidge, Ariz. "Some bright spots come and go from image to image. Other bright features persist and rotate around the pole, but at a rate slower than Saturn's rotation."
The UVIS images, which are also being analyzed by team associate Aikaterini Radioti at the University of Liege, Belgium, also suggest that one way the bright auroral storms may be produced is by the formation of new connections between magnetic field lines. That process causes storms in the magnetic bubble around Earth. The movie also shows one persistent bright patch of the aurora rotating in lockstep with the orbital position of Saturn's moon Mimas. While previous UVIS images had shown an intermittent auroral bright spot magnetically linked to the moon Enceladus, the new movie suggests another Saturn moon can influence the light show as well.
The new data also give scientists clues to a long-standing mystery about the atmospheres of giant outer planets.