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The Io Torus of Jupiter
NASA/JPL/University of Arizona
Video: 82 kB, Quicktime MOV
The Io torus is a doughnut-shaped ring of gas surrounding Jupiter. The gas originates from the many volcanoes on Io, Jupiter's closest large satellite. The volcanoes on Io spew out sulfur and sulfur dioxide. These particles are ejected into space and are stripped of their electrons (or ionized). The particles (ions) then become trapped in Jupiter's magnetic field. Because the field rotates with the planet, the particles make a complete circle around the planet every ten hours, the rotational period of Jupiter.
About the images
This video clip was compiled from 235 exposures taken in November 2000 by the Cassini spacecraft. The exposures were made using the ultraviolet imaging spectrograph while Cassini was about 50 million kilometers (30 million miles) from Jupiter. The moving dot above and below the image indicates the rotation of the planet. As the planet rotates, the torus appears to wobble because Jupiter's magnetic field is tilted relative to its poles.
Ellen Cohen
Io in Eclipse
NASA/JPL/University of Arizona
Video: 936 kB, MPEG
In this movie, the inner-most satellite of Jupiter, Io, is in the eclipse shadow of Jupiter (Jupiter is blocking the Sun for Io). This allowed NASA's spacecraft Cassini to image the active moon in darkness. These images were taken over a two-hour period and nearly capture the entire eclipse which took place on January 1, 2001. The spacecraft was over 10 million kilometers (6.3 million miles) away, yielding a resolution of 61 kilometers (40 miles) per pixel on these images.
Glows on Io
While Io is enshrouded in darkness, several glows are revealed to us. The bright points of light are hot lava from the active volcanoes on Io. The brightest of these is the volcano Pele which appears to be erupting constantly. To the right and slightly above Pele is a pair of bright spots from the volcano Pillan, the source of a major eruption in 1997. A second source of glow on Io is the faint, diffuse emission of atmospheric aurorae. Similar to the aurora borealis (northern lights) on Earth, the aurorae on Io result from collisions of charged particles (from the electrical currents that flow between Jupiter and Io) with gases in Io's tenuous atmosphere. The aurorae are seen here as a faint glow around Io's equator.
Ellen Cohen
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